Acquisitions and Discontinued Operations - Combined Results of Discontinued Operations (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income taxes	$ (2)	$ (10)	$ 3	$ (24)
Income (loss) from discontinued operations, net of taxes	(3)	(17)	5	(41)
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	9	26	29	74
Provision for credit losses	7	5	9	15
Net interest income after provision for credit losses	2	21	20	59
Noninterest income	(2)	(41)	1	(101)
Noninterest expense	5	7	13	23
Income (loss) before income taxes	(5)	(27)	8	(65)
Income taxes	(2)	(10)	3	(24)
Income (loss) from discontinued operations, net of taxes	$ (3)	$ (17)	$ 5	$ (41)