Fair Value Measurements (Reconciliation of Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs) (Level 3) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		$ 961	$ 902	$ 861	$ 804
Included in earnings		(8)	(53)	(9)	(94)
Purchases/originations		58	32	139	206
Settlements		11	(25)	(6)	(67)
Transfers Into Level 3	[1]	15	4	52	11
Ending Balance		1,037	860	1,037	860
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held	[2]	(19)	(68)	(54)	(157)
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		162	142	137	143
Included in earnings		(1)	0	(5)	2
Purchases/originations		0	0	0	0
Settlements		(4)	(6)	(12)	(16)
Transfers Into Level 3		15	4	52	11
Ending Balance		172	140	172	140
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held		(1)	0	(5)	2
Servicing Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		959	849	858	744
Included in earnings		(8)	(34)	8	(104)
Purchases/originations		59	33	144	208
Settlements		0	0	0	0
Transfers Into Level 3		0	0	0	0
Ending Balance		1,010	848	1,010	848
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held		(8)	(34)	8	(104)
Interest Rate Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		4	9	3	8
Included in earnings		18	28	54	77
Purchases/originations		(1)	(1)	(5)	(2)
Settlements		(22)	(28)	(53)	(75)
Transfers Into Level 3		0	0	0	0
Ending Balance		(1)	8	(1)	8
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held		7	13	9	14
Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		(164)	(98)	(137)	(91)
Included in earnings		(17)	(47)	(66)	(69)
Purchases/originations		0	0	0	0
Settlements		37	9	59	24
Transfers Into Level 3		0	0	0	0
Ending Balance		(144)	(136)	(144)	(136)
The amount of total gains or losses for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held		$ (17)	$ (47)	$ (66)	$ (69)

[1] Includes certain residential mortgage loans originated as held for sale that were transferred to held for invest ment.

[2] Includes interest income and expense .