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 Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]      
Long-term borrowings $ 9,206,000 $ 9,206,000 $ 8,309,000
Subordinated Notes      
Debt Instrument [Line Items]      
Long-term borrowings 5,733,000 5,733,000 4,821,000
Subordinated Notes | 3.86% Huntington National Bank subordinated notes due 2026      
Debt Instrument [Line Items]      
Long-term borrowings $ 238,000 $ 238,000 239,000
Stated rate 3.86% 3.86%  
Subordinated Notes | 3.86% Huntington National Bank subordinated notes due 2026      
Debt Instrument [Line Items]      
Long-term borrowings $ 129,000 $ 129,000 132,000
Stated rate 6.67% 6.67%  
Subordinated Notes | 5.45% Huntington National Bank subordinated notes due 2019      
Debt Instrument [Line Items]      
Long-term borrowings $ 77,000 $ 77,000 81,000
Stated rate 5.45% 5.45%  
Senior Notes | 2.24% Huntington National Bank senior notes due 2018      
Debt Instrument [Line Items]      
Long-term borrowings $ 844,000 $ 844,000 844,000
Stated rate 2.24% 2.24%  
Senior Notes | 2.10% Huntington National Bank senior notes due 2018      
Debt Instrument [Line Items]      
Long-term borrowings $ 748,000 $ 748,000 747,000
Stated rate 2.10% 2.10%  
Senior Notes | 2.47% Huntington National Bank senior notes due 2020      
Debt Instrument [Line Items]      
Long-term borrowings $ 694,000 $ 694,000 0
Stated rate 2.47% 2.47%  
Senior Notes | 2.55% Huntington National Bank senior notes due 2022      
Debt Instrument [Line Items]      
Long-term borrowings $ 685,000 $ 685,000 0
Stated rate 2.50% 2.50%  
Senior Notes | 2.43% Huntington National Bank senior notes due 2020      
Debt Instrument [Line Items]      
Long-term borrowings $ 498,000 $ 498,000 498,000
Stated rate 2.43% 2.43%  
Senior Notes | 2.23% Huntington National Bank senior note due 2019      
Debt Instrument [Line Items]      
Long-term borrowings $ 497,000 $ 497,000 500,000
Stated rate 2.23% 2.23%  
Senior Notes | 1.75% Huntington National Bank senior notes due 2018      
Debt Instrument [Line Items]      
Long-term borrowings $ 496,000 $ 496,000 500,000
Stated rate 1.75% 1.75%  
Senior Notes | 2.97% Huntington National Bank senior notes due 2020      
Debt Instrument [Line Items]      
Long-term borrowings $ 492,000 $ 492,000 495,000
Stated rate 2.97% 2.97%  
Senior Notes | 2.20% Huntington National Bank senior notes due 2020 (5)      
Debt Instrument [Line Items]      
Long-term borrowings $ 300,000 $ 300,000 0
Stated rate 1.71% 1.71%  
Senior Notes | 5.04% Huntington National Bank medium-term notes due 2018      
Debt Instrument [Line Items]      
Long-term borrowings $ 35,000 $ 35,000 36,000
Stated rate 5.04% 5.04%  
Senior Notes | 2.23% Huntington National Bank senior note due 2017      
Debt Instrument [Line Items]      
Long-term borrowings $ 0 $ 0 499,000
Stated rate 2.23% 2.23%  
Senior Notes | 1.42% Huntington National Bank senior notes due 2017      
Debt Instrument [Line Items]      
Long-term borrowings $ 0 $ 0 250,000
Stated rate 1.42% 1.42%  
Effective rate 0.74% 0.74%  
Senior Notes | 2.23% Huntington National Bank senior note due 2017      
Debt Instrument [Line Items]      
Basis spread on variable rate 5100.00%    
Senior Notes | London Interbank Offered Rate (LIBOR) [Member] | 1.42% Huntington National Bank senior notes due 2017      
Debt Instrument [Line Items]      
Basis spread on variable rate   0.425%  
Federal Home Loan Bank advances      
Debt Instrument [Line Items]      
Long-term borrowings $ 7,000 $ 7,000 8,000
Other borrowings      
Debt Instrument [Line Items]      
Long-term borrowings $ 338,000 $ 338,000 335,000
Other borrowings | Federal Home Loan Bank advances      
Debt Instrument [Line Items]      
Effective rate 3.51% 3.51%  
Other borrowings | Huntington Technology Finance nonrecourse debt, 3.63% effective interest rate, varying maturities      
Debt Instrument [Line Items]      
Long-term borrowings $ 263,000 $ 263,000 278,000
Effective rate 3.63% 3.63%  
Other borrowings | 3.57% Huntington Preferred Capital II - Class F securities      
Debt Instrument [Line Items]      
Long-term borrowings $ 75,000 $ 75,000 0
Stated rate 3.57% 3.57%  
Other borrowings | Huntington Technology Finance ABS Trust 2014 1.70% due 2020      
Debt Instrument [Line Items]      
Long-term borrowings $ 0 $ 0 57,000
Stated rate 1.70% 1.70%  
Other borrowings | London Interbank Offered Rate (LIBOR) [Member] | 3.57% Huntington Preferred Capital II - Class F securities      
Debt Instrument [Line Items]      
Basis spread on variable rate   1.88%  
Parent Company      
Debt Instrument [Line Items]      
Long-term borrowings $ 3,128,000 $ 3,128,000 3,145,000
Parent Company | Subordinated Notes | 7.00% Huntington Bancshares Incorporated subordinated notes due 2020      
Debt Instrument [Line Items]      
Long-term borrowings $ 312,000 $ 312,000 320,000
Stated rate 7.00% 7.00%  
Parent Company | Subordinated Notes | 3.55% Huntington Bancshares Incorporated subordinated notes due 2023      
Debt Instrument [Line Items]      
Long-term borrowings $ 245,000 $ 245,000 248,000
Stated rate 3.55% 3.55%  
Parent Company | Subordinated Notes | Huntington Capital I Trust Preferred 2.39% junior subordinated debentures due 2027      
Debt Instrument [Line Items]      
Long-term borrowings $ 69,000 $ 69,000 69,000
Effective rate 2.39% 2.39%  
Parent Company | Subordinated Notes | Sky Financial Capital Trust IV 1.73% Junior Subordinated Debentures Due 2036      
Debt Instrument [Line Items]      
Long-term borrowings $ 74,000 $ 74,000 74,000
Effective rate 3.09% 3.09%  
Parent Company | Subordinated Notes | Sky Financial Capital Trust III 2.40% Junior Subordinated Debentures Due 2036 [Member]      
Debt Instrument [Line Items]      
Long-term borrowings $ 72,000 $ 72,000 72,000
Effective rate 3.09% 3.09%  
Parent Company | Subordinated Notes | Huntington Capital II Trust Preferred 1.14% junior subordinated debentures due 2028      
Debt Instrument [Line Items]      
Long-term borrowings $ 31,000 $ 31,000 32,000
Effective rate 1.76% 1.76%  
Parent Company | Subordinated Notes | Camco Statutory Trust I 2.95% due 2037      
Debt Instrument [Line Items]      
Long-term borrowings $ 4,000 $ 4,000 4,000
Effective rate 3.02% 3.02%  
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Huntington Capital I Trust Preferred 2.39% junior subordinated debentures due 2027      
Debt Instrument [Line Items]      
Basis spread on variable rate   0.70%  
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Sky Financial Capital Trust IV 1.73% Junior Subordinated Debentures Due 2036      
Debt Instrument [Line Items]      
Basis spread on variable rate   1.40%  
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Sky Financial Capital Trust III 2.40% Junior Subordinated Debentures Due 2036 [Member]      
Debt Instrument [Line Items]      
Basis spread on variable rate   1.40%  
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Huntington Capital II Trust Preferred 1.14% junior subordinated debentures due 2028      
Debt Instrument [Line Items]      
Basis spread on variable rate   0.625%  
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | Camco Statutory Trust I 2.95% due 2037      
Debt Instrument [Line Items]      
Basis spread on variable rate   1.33%  
Parent Company | Subordinated Notes | London Interbank Offered Rate (LIBOR) [Member] | 2.20% Huntington National Bank senior notes due 2020 (5)      
Debt Instrument [Line Items]      
Basis spread on variable rate   0.51%  
Parent Company | Senior Notes | 3.19% Huntington Bancshares Incorporated medium-term notes due 2021      
Debt Instrument [Line Items]      
Long-term borrowings $ 969,000 $ 969,000 973,000
Parent Company | Senior Notes | 2.33% Huntington Bancshares Incorporated senior note due 2022      
Debt Instrument [Line Items]      
Long-term borrowings 953,000 953,000 954,000
Parent Company | Senior Notes | 2.64% Huntington Bancshares Incorporated senior note due 2018      
Debt Instrument [Line Items]      
Long-term borrowings $ 399,000 $ 399,000 $ 399,000
Stated rate 3.19% 3.19%