Basis of Presentation - Line of Business Financial Performance (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Line Of Business Financial Performance [Line Items]
Revenue generated from certain contracts with customers included in noninterest income	$ 1,800	$ 1,700	$ 5,500	$ 5,200
Payment Services [Member]
Line Of Business Financial Performance [Line Items]
Rewards and rebate costs and certain partner payments included in noninterest income	$ 539	$ 504	$ 1,600	$ 1,500