MSR (Activity Related to the MSR Portfolio) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Servicing Assets at Fair Value
Securities gains (losses), net - non-qualifying hedges on mortgage servcing rights		$ (1)	$ 2	$ (18)	$ 4
MSR fair value adjustments due to change in inputs or assumptions	[1]	25	(2)	103	(15)
Interest Rate Contract | Servicing Rights | Mortgage Banking Revenue
Servicing Assets at Fair Value
Changes in fair value and settlement of free-standing derivatives purchased to economically hedge the MSR portfolio (Mortgage banking net revenue)	[1]	$ (24)	$ 1	$ (89)	$ 16

[1] (a) Included in mortgage banking net revenue in the Condensed Consolidated Statements of Income.