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	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	$ 804		$ 380		$ 484
Included in earnings	(107)		130		399
Purchases	234		(3)		(2)
Sale and exercise of warrant			(334)
Sales					(477)
Settlements	(86)		(131)		(111)
Transfers into Level 3	16	[1]	18	[2]	87	[3]
Ending balance	861		804		380
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	(191)	[4]	(45)	[5]	83	[6]
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	143		167		108
Included in earnings	1		(2)		0
Purchases	0		0		0
Settlements	(23)		(40)		(28)
Transfers into Level 3	16	[1]	18	[2]	87	[3]
Ending balance	137		143		167
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	[4]	(2)	[5]	0	[6]
Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	744
Included in earnings	(122)
Purchases	(236)
Settlements	0
Transfers into Level 3	0
Ending balance	858		744
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	(122)
Interest Rate Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	8	[7]	12	[8]	10	[9]
Included in earnings	94	[7]	115	[8]	111	[9]
Purchases	2	[7]	(3)	[8]	(2)	[9]
Settlements	(97)	[7]	(116)	[8]	(107)	[9]
Transfers into Level 3	0	[1]	0		0
Ending balance	3	[7]	8	[7]	12	[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	10	[4],[7]	13	[5],[8]	17	[6],[9]
Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	(91)	[8]	201	[9]	366	[9]
Included in earnings	(80)	[7]	17	[8]	288	[9]
Purchases			0		0
Sale and exercise of warrant	0	[7]	(334)	[8]	477	[9]
Settlements	34	[7]	25	[8]	24	[9]
Transfers into Level 3	0		0		0
Ending balance	(137)	[7]	(91)	[8]	201	[9]
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	$ (80)	[4],[7]	$ (56)	[5],[8]	$ 66	[6],[9]

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

[2] Includes certain residential mortgage loans held for sale that were transferred to held for investment.

[3] Includes certain residential mortgage loans held for sale that were transferred to held for investment.

[4] Includes interest income and expense.

[5] Includes interest income and expense.

[6] Includes interest income and expense.

[7] Net interest rate derivatives include derivative assets and liabilities of $ 8 and $ 5 , respectively, as of December 31, 2017 .

[8] Net interest rate derivatives include derivative assets and liabilities of $ 13 and $ 5 , respect ively, as of December 31, 2016 . Net equity derivatives include derivative assets and liabilities of $ 0 and $ 91 , respectively, as of December 31, 2016 .

[9] Net interest rate derivatives include derivative assets and liabilities of $ 15 and $ 3 , respectively, as of December 31, 2015 . Net equity derivatives include derivative assets and liabilities of $ 262 and $ 61 , respectively, as of December 31, 2015 .