Fair Value Option Elected, Difference Between the Aggregate Fair Value and the Aggregate Unpaid Principal Balance (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014		Dec. 31, 2014
Loans Receivable, Fair Value Disclosure	$ 262				$ 262				$ 272
Fair Value, Option, Aggregate Differences, Long-term Debt Instruments	79				79				107
Trading Loans [Member]
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	52				52				21
Loans Receivable, Fair Value Disclosure	2,739				2,739				2,610
Aggregate Unpaid Principal Balance Under the Fair Value Option	(2,687)				(2,687)				(2,589)
Loans Held For Sale [Member]
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	77				77				74
Loans Receivable, Fair Value Disclosure	1,883				1,883				1,891
Aggregate Unpaid Principal Balance Under the Fair Value Option	(1,806)				(1,806)				(1,817)
Loans Held For Investment [Member]
Fair Value, Option, Aggregate Differences, Loans and Long-term Receivables	(9)				(9)				(12)
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference	(1)				(1)				(2)
Loans Receivable, Fair Value Disclosure	260				260				269
Aggregate Unpaid Principal Balance Under the Fair Value Option	(269)				(269)				(281)
Long-Term Debt [Domain]
Obligations, Fair Value Disclosure	986				986				1,283
Aggregate Unpaid Principal Balance Under the Fair Value Option	907				907				1,176
Loans Held For Investment [Member]
Fair Value, Option, Changes in Fair Value, Gain (Loss)	4		$ 0	[1]	3	[2]	$ 8	[1]
Nonaccrual loans	2				2				3
Loans Held For Investment [Member] | Aggregate Unpaid Principal Balance Under Fair Value Option
Nonaccrual loans	3				3				5
Loans Held For Sale [Member]
Fair Value, Option, Changes in Fair Value, Gain (Loss)	20	[2]	(32)	[1]	32	[2]	(18)	[1]
Nonaccrual loans									1
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregated Difference									0
Loans Held For Sale [Member] | Aggregate Unpaid Principal Balance Under Fair Value Option
Nonaccrual loans									$ 1
Mortgage Servicing Income [Member] | Loans Held For Investment [Member]
Fair Value, Option, Changes in Fair Value, Gain (Loss)	0		0		0		0
Mortgage Servicing Income [Member] | Loans Held For Sale [Member]
Fair Value, Option, Changes in Fair Value, Gain (Loss)	$ 0		$ 0		$ 0		$ 0

[1] Changes in fair value for the three and nine months ended September 30, 2014 exclude accrued interest for the period then ended. Interest income or interest expense on trading loans, LHFS, LHFI, brokered time deposits, and long-term debt that have been elected to be measured at fair value are recognized in interest income or interest expense in the Consolidated Statements of Income.

[2] Changes in fair value for the three and nine months ended September 30, 2015 exclude accrued interest for the period then ended. Interest income or interest expense on trading loans, LHFS, LHFI, and long-term debt that have been elected to be measured at fair value are recognized in interest income or interest expense in the Consolidated Statements of Income.