Receivables Held for Sale - Summary of Components of Cumulative Lower of Amortized Cost or Fair Value Adjustment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Real Estate Owned [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Lower Of Cost Or Fair Value Adjustment On Loans Held For Sale Including Credit Component	$ 0		$ 4
Short Sales [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Lower Of Cost Or Fair Value Adjustment On Loans Held For Sale Including Credit Component	1		1
Other Income [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Initial lower of amortized cost or fair value adjustment	0		60
Subsequent to initial transfer to held for sale	17		(171)
Lower of amortized cost or fair value adjustment recorded through other revenues(1)	17	[1]	(111)	[1]
Other Income [Member] | Fair Value [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Initial lower of amortized cost or fair value adjustment	0		60
Subsequent to initial transfer to held for sale	16		(176)
Lower of amortized cost or fair value adjustment recorded through other revenues(1)	16	[1]	(116)	[1]
Other Income [Member] | Real Estate Owned [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Initial lower of amortized cost or fair value adjustment	0		0
Subsequent to initial transfer to held for sale	0		4
Lower of amortized cost or fair value adjustment recorded through other revenues(1)	0	[1]	4	[1]
Other Income [Member] | Short Sales [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Initial lower of amortized cost or fair value adjustment	0		0
Subsequent to initial transfer to held for sale	1		1
Lower of amortized cost or fair value adjustment recorded through other revenues(1)	$ 1	[1]	$ 1	[1]

[1] During three months ended March 31, 2015 and 2014, no lower of amortized cost or fair value adjustment was recorded as a provision for credit losses.