Basis of Presentation - Line of Business Financial Performance (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Line Of Business Financial Performance [Line Items]
Revenue generated from certain contracts with customers included in noninterest income	$ 1,900	$ 1,800	$ 3,700	$ 3,500
Payment Services [Member]
Line Of Business Financial Performance [Line Items]
Rewards and rebate costs and certain partner payments included in noninterest income	$ 533	$ 493	$ 1,100	$ 961