Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,780	$ 2,642	$ 2,645	$ 2,591
Rights purchased	2	4	4	6
Rights capitalized	97	82	197	204
Changes in fair value of MSRs
Due to fluctuations in market interest rates	38	(50)	152	(30)
Due to revised assumptions or models	26	5	50	17
Other changes in fair value	(99)	(101)	(204)	(206)
Balance at end of period	$ 2,844	$ 2,582	$ 2,844	$ 2,582