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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Real Estate Owned [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Lower of amortized cost or fair value adjustment	$ 2	$ (1)	$ 4	$ (50)
Short Sales [Member]
Lower of amortized cost or fair value adjustment recorded as a component of:
Lower of amortized cost or fair value adjustment	1	(11)	2	(22)
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	10	46	112	145
Subsequent to initial transfer to held for sale	(94)	(112)	(404)	(1,037)
Lower of amortized cost or fair value adjustment recorded through other revenues	(84)	(66)	(292)	(892)
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	10	46	112	145
Subsequent to initial transfer to held for sale	(97)	(100)	(410)	(965)
Lower of amortized cost or fair value adjustment recorded through other revenues	(87)	(54)	(298)	(820)
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	0	0
Subsequent to initial transfer to held for sale	2	(1)	4	(50)
Lower of amortized cost or fair value adjustment recorded through other revenues	2	(1)	4	(50)
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	0	0
Subsequent to initial transfer to held for sale	1	(11)	2	(22)
Lower of amortized cost or fair value adjustment recorded through other revenues	$ 1	$ (11)	$ 2	$ (22)