Mortgage Servicing Rights - Changes in Fair Value of Capitalized MSRs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Transfers and Servicing of Financial Assets [Abstract]
Balance at beginning of period	$ 2,713	$ 1,840	$ 2,210	$ 2,546
Rights purchased	9	8	36	16
Rights capitalized	284	321	896	712
Rights sold	0	1	1	3
Changes in fair value of MSRs
Due to fluctuations in market interest rates	53	(8)	307	(815)
Due to revised assumptions or models	(30)	(7)	(169)	37
Other changes in fair value	(119)	(177)	(371)	(521)
Balance at end of period	$ 2,910	$ 1,978	$ 2,910	$ 1,978