Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT - Narrative (Details)

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LONG-TERM DEBT - Narrative (Details) - USD ($)
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Dec. 31, 2018
Aug. 16, 2018
May 08, 2018
Dec. 31, 2017
Aug. 07, 2017
Mar. 07, 2017
Debt Instrument [Line Items]              
Long-term debt $ 8,625,000,000 $ 8,625,000,000     $ 9,206,000,000    
Senior Notes | Huntington National Bank Senior Note Due May 2025, 4.00 Percent [Member]              
Debt Instrument [Line Items]              
Debt face amount       $ 500,000,000      
Debt percent of value issued       99.686%      
Stated rate       4.00%      
Senior Notes | Huntington National Bank Senior Note Due May 2021, 3.25 Percent [Member]              
Debt Instrument [Line Items]              
Debt face amount       $ 750,000,000      
Debt percent of value issued       99.774%      
Stated rate       3.25%      
Senior Notes | Huntington National Bank Senior Note Due October 2023, 3.55 Percent [Domain]              
Debt Instrument [Line Items]              
Debt face amount     $ 750,000,000        
Debt percent of value issued     99.78%        
Stated rate     3.55%        
Senior Notes | Senior notes due 2020              
Debt Instrument [Line Items]              
Debt face amount             $ 700,000,000
Debt percent of value issued             99.994%
Stated rate             2.375%
Redemption price percentage 100.00%            
Senior Notes | 2.23% Huntington National Bank senior note due 2017              
Debt Instrument [Line Items]              
Debt face amount             $ 300,000,000
Debt percent of value issued             100.00%
Senior Notes | Huntington National Bank Senior Note Due August 2022, 2.5 Percent [Member]              
Debt Instrument [Line Items]              
Debt face amount           $ 700,000,000  
Debt percent of value issued           99.762%  
Stated rate           2.50%  
Subordinated Notes              
Debt Instrument [Line Items]              
Long-term debt $ 4,957,000,000 4,957,000,000     5,733,000,000    
Other borrowings              
Debt Instrument [Line Items]              
Long-term debt 446,000,000 446,000,000     338,000,000    
Parent Company              
Debt Instrument [Line Items]              
Long-term debt $ 3,216,000,000 $ 3,216,000,000     3,128,000,000    
Parent Company | Subordinated Notes | Huntington Capital II Trust Preferred 3.42% junior subordinated debentures due 2028              
Debt Instrument [Line Items]              
Effective rate 3.42% 3.42%          
Long-term debt $ 31,000,000 $ 31,000,000     $ 31,000,000    
Parent Company | Subordinated Notes | Huntington Capital II Trust Preferred 3.42% junior subordinated debentures due 2028 | London Interbank Offered Rate (LIBOR) [Member]              
Debt Instrument [Line Items]              
Basis spread on variable rate   0.625%