MSR (Changes in the Servicing Assets) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Servicing Assets at Fair Value
Fair value at beginning of period	$ 858	$ 744
Servicing rights originated	16	26
Servicing rights acquired	24	29
Changes in fair value due to changes in inputs or assumptions	57	4	[1]
Changes in fair value due to other changes in fair value	(29)	(27)	[2]
Fair value at end of period	$ 926	$ 776

[1] Primarily reflects changes in prepayment speed and OAS spread assumptions which are updated based on market interest rates

[2] Pr imarily reflects changes due to collection of contractual cash flows and the passage of time