Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,787	$ 1,887	$ 2,210	$ 2,546
Rights purchased	11	3	27	8
Rights capitalized	293	190	612	391
Rights sold	1	1	1	2
Changes in fair value of MSRs
Due to fluctuations in market interest rates	(232)	(64)	254	(807)
Due to revised assumptions or models	(37)	27	(139)	44
Other changes in fair value	(110)	(204)	(252)	(344)
Balance at end of period	$ 2,713	$ 1,840	$ 2,713	$ 1,840