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Accumulated Other Comprehensive Loss - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Tax (benefit) expense included in net unrealized gains (losses), investment securities $ (63) $ 64    
Tax included in reclassification, investment securities (1) (2)    
Tax included in amortization, investment securities 1 3    
Tax (benefit) expense included in net unrealized gains (losses), fair value option liabilities 5 (46)    
Tax (benefit) expense included in net unrealized gains (losses), cash flow hedges (less than $1 million in all periods) (1) (1)    
Tax included in reclassification, cash flow hedges 1 1    
Tax included in net unrealized gains (losses), pension and postretirement benefit liability $ 1 $ 0    
Unrealized Gains (Losses) on Investment Securities [Member] | Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Cumulative effect of new accounting principle in period of adoption, tax     $ 2 $ 0
Unrealized Gains (Losses) on Fair Value Option Liabilities Attributable to Our Own Credit Spread [Member] | Accounting Standards Update 2016-01, Fair Value Option [Member]        
Accumulated Other Comprehensive Income (Loss) [Line Items]        
Cumulative effect of new accounting principle in period of adoption, tax     $ 0 $ 103