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
		Mar. 31, 2018		Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		$ 861		$ 804
Included in earnings		1		(13)
Purchases/originations		38		54
Settlements		(135)		(17)
Transfers Into Level 3	[1]	136		3
Ending Balance		901		831
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]	(2)		(20)
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		137		143
Included in earnings		(2)		0
Purchases/originations		0		0
Settlements		(135)		(5)
Transfers Into Level 3	[1]	136		3
Ending Balance		136		141
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]	(2)		0
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		858		744
Included in earnings		28		(23)
Purchases/originations		40		55
Settlements		0		0
Transfers Into Level 3		0	[1]	0
Ending Balance		926		776
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		28	[2]	(23)
Interest Rate Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance	[3]	3		8	[4]
Included in earnings		14	[3]	23	[4]
Purchases/originations		(2)	[3]	(1)	[4]
Settlements		(11)	[3]	(19)	[4]
Transfers Into Level 3	[1]	0	[3]	0	[4]
Ending Balance		4	[3]	11	[4]
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]	11	[3]	16	[4]
Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		(137)		(91)	[4]
Included in earnings		(39)		(13)	[4]
Purchases/originations		0		0	[4]
Settlements		11		7	[4]
Transfers Into Level 3	[1]	0		0	[4]
Ending Balance		(165)		(97)	[4]
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]	$ (39)		$ (13)	[4]

[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 .

[3] Net interest rate derivatives include derivative assets and liabilities of $ 11 and $ 7 , respectively , as of March 31, 2018 .

[4] Net interest rate derivatives include derivative assets and liabilities of $ 16 and $ 5 , respectively, as of March 31, 2017 . Net equity derivatives include derivative assets and liabilities of $ 0 and $ 97 , respectively, as of March 31, 2017 .