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, 2016		Dec. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	$ 380		$ 484		$ 437
Included in earnings	130		399		122
Purchases	(3)		(2)		(1)
Sale and exercise of warrant	(334)		(477)
Sales					(1)
Settlements	(131)		(111)		(102)
Transfers into Level 3	18	[1]	87	[2]	29	[3]
Ending balance	60		380		484
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	(45)	[4]	83	[5]	10	[6]
Trading Securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance			0		1
Sales					(1)
Ending balance					0
Residential Mortgage
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	167		108		92
Included in earnings	(2)		0		4
Settlements	(40)		(28)		(17)
Transfers into Level 3	18	[1]	87	[2]	29	[3]
Ending balance	143		167		108
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)	[4]	0	[5]	4	[6]
Interest Rate Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	12	[7]	10	[8]	8	[9]
Included in earnings	115	[7]	111	[8]	125	[9]
Purchases	(3)	[7]	(2)	[8]	(1)	[9]
Settlements	(116)	[7]	(107)	[8]	(122)	[9]
Ending balance	8	[7]	12	[7]	10	[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	13	[4],[7]	17	[5],[8]	13	[6],[9]
Equity Contract
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Beginning balance	201	[8]	366	[9]	336	[9]
Included in earnings	17	[7]	288	[8]	(7)	[9]
Sale and exercise of warrant	(334)	[7]	(477)	[8]
Settlements	25	[7]	24	[8]	37	[9]
Ending balance	(91)	[7]	201	[8]	366	[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	$ (56)	[4],[7]	$ 66	[5],[8]	$ (7)	[6],[9]

[1] Includes certain residential mortgage loans 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 $ 13 and $ 5 , respectively, as of December 31, 2016 . Net equity derivatives include derivative assets and liabilities of $ 0 and $ 91 , respectively, as of December 31, 2016 .

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

[9] Net interest rate derivatives include derivative assets and liabilities of $ 12 and $ 2 , respectively, as of December 31, 2014 . Net equity derivatives include derivative assets and liabilities of $ 415 and $ 49 , respectively, as of December 31, 2014 .