Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE FINANCIAL INSTRUMENTS - Asset and Liability Management (Details)

v3.8.0.1
DERIVATIVE FINANCIAL INSTRUMENTS - Asset and Liability Management (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Credit Derivatives [Line Items]    
Average maturity of interest rate derivative in years 2 years 5 months 1 day  
Notional Disclosures [Abstract]    
Derivative, Notional Amount $ 7,852 $ 8,375
Fair Value Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 7,840 8,375
Cash Flow Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 12 0
Subordinated notes    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 950 950
Subordinated notes | Fair Value Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 950 950
Subordinated notes | Cash Flow Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 0 0
Securities Investment [Member]    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 12  
Securities Investment [Member] | Fair Value Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 0  
Securities Investment [Member] | Cash Flow Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 12  
Other long-term debt    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 6,890 7,425
Other long-term debt | Fair Value Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount 6,890 7,425
Other long-term debt | Cash Flow Hedging    
Notional Disclosures [Abstract]    
Derivative, Notional Amount $ 0 $ 0
Asset conversion swaps Receive Fixed Generic [Member]    
Credit Derivatives [Line Items]    
Average maturity of interest rate derivative in years 1 year 11 months 15 days 0 years
Liability conversion swaps Receive Fixed Generic [Member]    
Credit Derivatives [Line Items]    
Average maturity of interest rate derivative in years   2 years 6 months