Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT - Narrative (Details)

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LONG-TERM DEBT - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Debt Instrument [Line Items]    
Long-term debt $ 9,849 $ 8,625
Subordinated Notes    
Debt Instrument [Line Items]    
Long-term debt 5,263 4,957
Other borrowings    
Debt Instrument [Line Items]    
Long-term debt 486 446
Parent Company    
Debt Instrument [Line Items]    
Long-term debt $ 4,095 3,216
Parent Company | Subordinated Notes | Huntington Capital II Trust Preferred 2.53% junior subordinated debentures due 2028 (3)    
Debt Instrument [Line Items]    
Effective rate 2.53%  
Long-term debt $ 32 $ 31
Parent Company | Subordinated Notes | Huntington Capital II Trust Preferred 2.53% junior subordinated debentures due 2028 (3) | London Interbank Offered Rate (LIBOR) [Member]    
Debt Instrument [Line Items]    
Basis spread on variable rate 0.625%