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				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		$ 901		$ 831		$ 861		$ 804
Included in earnings		(2)		(29)		(1)		(42)
Purchases/originations		45		120		81		174
Settlements		(15)		(24)		(17)		(41)
Transfers Into Level 3	[1]	32		4		37		7
Ending Balance		961		902		961		902
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]	(12)		(41)		(25)		(76)
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		136		141		137		143
Included in earnings		(1)		1		(4)		1
Purchases/originations		0		0		0		0
Settlements		(5)		(4)		(8)		(9)
Transfers Into Level 3	[1]	32		4		37		7
Ending Balance		162		142		162		142
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]	(1)		1		(4)		1
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance		926		776		858		744
Included in earnings		(13)		(47)		16		(70)
Purchases/originations		46		120		(85)		175
Settlements		0		0		0		0
Transfers Into Level 3		0	[1]	0		0	[1]	0
Ending Balance		959		849		959		849
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		(13)	[2]	(47)		(16)	[2]	(70)
Interest Rate Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance	[3],[4],[5]	4		11		3		8
Included in earnings		22	[5]	26	[3],[4]	36	[5]	49	[3],[4]
Purchases/originations		(1)	[5]	0	[3],[4]	(4)	[5]	(1)	[3],[4]
Settlements		(21)	[5]	(28)	[3],[4]	(31)	[5]	(47)	[3],[4]
Transfers Into Level 3	[1]	0	[5]	0	[3],[4]	0	[5]	0	[3],[4]
Ending Balance		4	[5]	9	[3],[4]	4	[5]	9	[3],[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]	12	[5]	14	[3],[4]	12	[5]	15	[3],[4]
Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning Balance	[3],[4]	(165)		(97)		(137)		(91)
Included in earnings		(10)		(9)	[3],[4]	(49)		(22)	[3],[4]
Purchases/originations		0		0	[3],[4]	0		0	[3],[4]
Settlements		11		8	[3],[4]	22		15	[3],[4]
Transfers Into Level 3	[1]	0		0	[3],[4]	0		0	[3],[4]
Ending Balance		(164)		(98)	[3],[4]	(164)		(98)	[3],[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]	$ (10)		$ (9)	[3],[4]	$ (49)		$ (22)	[3],[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 $14 and $5 , respectively, as of June 30, 2017 .

[4] Net interest rate derivatives include derivative assets and liabilities of $ 14 and $ 5 , respectively, as of June 30, 2017 .

[5] Net interest rate derivatives include derivative assets and liabilities of $ 11 and $ 7 , respectively , as of June 30, 2018 .