Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT - Schedule of Long-Term Debt (Details)

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LONG-TERM DEBT - Schedule of Long-Term Debt (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Aug. 01, 2019
Feb. 19, 2019
Jan. 29, 2019
Dec. 31, 2018
Debt Instrument [Line Items]          
Document Period End Date Dec. 31, 2019        
Long-term borrowings $ 9,849       $ 8,625
Subordinated Notes          
Debt Instrument [Line Items]          
Long-term borrowings 5,263       4,957
Subordinated Notes | 3.86% Huntington National Bank subordinated notes due 2026          
Debt Instrument [Line Items]          
Long-term borrowings $ 231       229
Stated rate 3.86%        
Subordinated Notes | 5.45% Huntington National Bank subordinated notes due 2019          
Debt Instrument [Line Items]          
Long-term borrowings $ 0       76
Stated rate 5.45%        
Senior Notes | 3.60% Huntington National Bank senior notes due 2023          
Debt Instrument [Line Items]          
Long-term borrowings $ 778       756
Effective rate 3.60%        
Senior Notes | 3.33% Huntington National Bank senior notes due 2021          
Debt Instrument [Line Items]          
Long-term borrowings $ 759       750
Effective rate 3.33%        
Senior Notes | 2.47% Huntington National Bank senior notes due 2020          
Debt Instrument [Line Items]          
Long-term borrowings $ 699       692
Stated rate 2.47%        
Senior Notes | 2.55% Huntington National Bank senior notes due 2022          
Debt Instrument [Line Items]          
Long-term borrowings $ 691       672
Effective rate 2.55%        
Senior Notes | 3.16% Huntington National Bank senior note due 2022          
Debt Instrument [Line Items]          
Long-term borrowings $ 507       0
Senior Notes | 2.43% Huntington National Bank senior note due 2020          
Debt Instrument [Line Items]          
Long-term borrowings $ 500       493
Stated rate 3.16%        
Senior Notes | 2.97% Huntington National Bank senior notes due 2020          
Debt Instrument [Line Items]          
Long-term borrowings $ 499       491
Stated rate 2.97%        
Senior Notes | 2.42% Huntington National Bank senior notes due 2020 (5)          
Debt Instrument [Line Items]          
Long-term borrowings $ 300       300
Effective rate 2.42%        
Senior Notes | 2.46% Huntington National Bank senior notes due 2021 (6)          
Debt Instrument [Line Items]          
Long-term borrowings $ 299       0
Effective rate 2.46%        
Senior Notes | 2.23% Huntington National Bank senior note due 2019          
Debt Instrument [Line Items]          
Long-term borrowings $ 0       498
Stated rate 2.43%        
Senior Notes | Huntington National Bank Senior Note Due February 2021, No Coupon Rate          
Debt Instrument [Line Items]          
Debt face amount       $ 300  
Debt percent of value issued 100.00%        
Senior Notes | Huntington National Bank Senior Note Due April 2022, 3.125 Percent          
Debt Instrument [Line Items]          
Stated rate       3.125%  
Debt face amount     $ 500    
Debt percent of value issued 99.909%        
Senior Notes | Huntington National Bank Senior Note Due August 2024 2.625 Percent          
Debt Instrument [Line Items]          
Stated rate   2.625%      
Debt face amount   $ 800      
Debt percent of value issued 99.781%        
Federal Home Loan Bank advances          
Debt Instrument [Line Items]          
Long-term borrowings $ 5       6
Other borrowings          
Debt Instrument [Line Items]          
Long-term borrowings $ 486       446
Other borrowings | Federal Home Loan Bank advances          
Debt Instrument [Line Items]          
Effective rate 3.01%        
Other borrowings | Huntington Technology Finance nonrecourse debt, 4.08% weighted average interest rate, varying maturities          
Debt Instrument [Line Items]          
Long-term borrowings $ 312       322
Effective rate 4.08%        
Other borrowings | 3.79% Huntington Preferred Capital II - Class F securities          
Debt Instrument [Line Items]          
Long-term borrowings $ 74       74
Effective rate 3.79%        
Other borrowings | 3.79% Huntington Preferred Capital II - Class G securities          
Debt Instrument [Line Items]          
Long-term borrowings $ 50       50
Effective rate 3.79%        
Other borrowings | 3.91% Huntington Preferred Capital II - Class I securities          
Debt Instrument [Line Items]          
Long-term borrowings $ 50       0
Effective rate 3.91%        
Other borrowings | London Interbank Offered Rate (LIBOR) [Member] | 3.79% Huntington Preferred Capital II - Class F securities          
Debt Instrument [Line Items]          
Basis spread on variable rate 1.88%        
Other borrowings | London Interbank Offered Rate (LIBOR) [Member] | 3.91% Huntington Preferred Capital II - Class I securities          
Debt Instrument [Line Items]          
Basis spread on variable rate 2.00%        
Parent Company          
Debt Instrument [Line Items]          
Long-term borrowings $ 4,095       3,216
Parent Company | Subordinated Notes | 7.00% Huntington Bancshares Incorporated subordinated notes due 2020          
Debt Instrument [Line Items]          
Long-term borrowings $ 305       305
Stated rate 7.00%        
Parent Company | Subordinated Notes | 3.55% Huntington Bancshares Incorporated subordinated notes due 2023          
Debt Instrument [Line Items]          
Long-term borrowings $ 247       239
Stated rate 3.55%        
Parent Company | Subordinated Notes | Sky Financial Capital Trust IV 3.31% junior subordinated debentures due 2036 (1)          
Debt Instrument [Line Items]          
Long-term borrowings $ 74       74
Effective rate 3.31%        
Parent Company | Subordinated Notes | Sky Financial Capital Trust III 3.31% junior subordinated debentures due 2036 (1)          
Debt Instrument [Line Items]          
Long-term borrowings $ 72       72
Effective rate 3.31%        
Parent Company | Subordinated Notes | Huntington Capital I Trust Preferred 2.61% junior subordinated debentures due 2027 (2)          
Debt Instrument [Line Items]          
Long-term borrowings $ 70       69
Effective rate 2.61%        
Parent Company | Subordinated Notes | Huntington Capital II Trust Preferred 2.53% junior subordinated debentures due 2028 (3)          
Debt Instrument [Line Items]          
Long-term borrowings $ 32       31
Effective rate 2.53%        
Parent Company | Subordinated Notes | Camco Financial Statutory Trust I 3.24% due 2037 (4)          
Debt Instrument [Line Items]          
Long-term borrowings $ 4       4
Effective rate 3.24%        
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Sky Financial Capital Trust IV 3.31% junior subordinated debentures due 2036 (1)          
Debt Instrument [Line Items]          
Basis spread on variable rate 1.40%        
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Huntington Capital I Trust Preferred 2.61% junior subordinated debentures due 2027 (2)          
Debt Instrument [Line Items]          
Basis spread on variable rate 0.70%        
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Huntington Capital II Trust Preferred 2.53% junior subordinated debentures due 2028 (3)          
Debt Instrument [Line Items]          
Basis spread on variable rate 0.625%        
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Camco Financial Statutory Trust I 3.24% due 2037 (4)          
Debt Instrument [Line Items]          
Basis spread on variable rate 1.33%        
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | 2.42% Huntington National Bank senior notes due 2020 (5)          
Debt Instrument [Line Items]          
Basis spread on variable rate 0.51%        
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | 2.46% Huntington National Bank senior notes due 2021 (6)          
Debt Instrument [Line Items]          
Basis spread on variable rate 0.55%        
Parent Company | Senior Notes | 3.19% Huntington Bancshares Incorporated medium-term notes due 2021          
Debt Instrument [Line Items]          
Long-term borrowings $ 993       969
Stated rate 3.19%        
Parent Company | Senior Notes | 2.33% Huntington Bancshares Incorporated senior notes due 2022          
Debt Instrument [Line Items]          
Long-term borrowings $ 972       946
Stated rate 2.33%        
Parent Company | Senior Notes | Huntington Bancshares Incorporated Senior Note Due 2024, 2.67 Percent [Member]          
Debt Instrument [Line Items]          
Effective rate 2.67%        
Parent Company | Senior Notes | 2.67% Huntington Bancshares Incorporated senior notes due 2024          
Debt Instrument [Line Items]          
Long-term borrowings $ 798       0
Parent Company | Senior Notes | 4.05% Huntington Bancshares Incorporated senior notes due 2025          
Debt Instrument [Line Items]          
Long-term borrowings $ 528       $ 507
Effective rate 4.05%