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Derivative Financial Instruments - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Derivative [Line Items]      
Notional amounts of derivative contracts entered into for trading account purposes $ 57,550,000,000 $ 19,850,000,000  
Net unrealized pre-tax gains related to hedged loans held for sale, commitments to originate loans for sale and commitments to sell loans 18,000,000 18,000,000  
Aggregate fair value of derivative financial instruments in a liability position 51,000,000 21,000,000  
Aggregate fair value of derivative financial instruments in asset position 6,000,000 18,000,000  
Collateral relating to net asset positions 5,000,000 16,000,000  
Counterparties [Member]      
Derivative [Line Items]      
Post collateral requirements relating to positions 50,000,000 18,000,000  
Clearinghouse Credit Facilities [Member]      
Derivative [Line Items]      
Amount of initial margin posted 84,000,000 65,000,000  
Interest Rate Swap Agreements [Member]      
Derivative [Line Items]      
Increase decrease in net interest income due to interest rate swap agreements (2,000,000) 25,000,000 $ 25,000,000
Notional amounts of derivative contracts entered into for trading account purposes 57,550,000,000    
Interest Rate Contracts [Member]      
Derivative [Line Items]      
Notional amounts of derivative contracts entered into for trading account purposes 48,600,000,000 42,900,000,000  
Foreign Currency and Other Option and Futures Contracts [Member]      
Derivative [Line Items]      
Notional amounts of derivative contracts entered into for trading account purposes 1,200,000 $ 763,000,000  
Credit Risk Derivative [Member]      
Derivative [Line Items]      
Fair value of additional collateral to be posted for derivative financial instruments $ 0