Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,642	$ 2,222	$ 2,591	$ 2,512
Rights purchased	4	6	6	14
Rights capitalized	82	131	204	230
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(50)	(187)	(30)	(488)
Due to revised assumptions or models	5		17
Other changes in fair value	(101)	(116)	(206)	(212)
Balance at end of period	$ 2,582	$ 2,056	$ 2,582	$ 2,056