Acquisitions and Discontinued Operations - Components of Income (Loss) from Discontinued Operations, Net of Taxes (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
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)
Discontinued Operations [Member] | Victory Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income		5		7
Noninterest income				10
Income (loss) before income taxes		5		17
Income taxes		2		7
Income (loss) from discontinued operations, net of taxes		$ 3		10
Discontinued Operations [Member] | Austin Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noninterest expense				4
Income (loss) before income taxes				(4)
Income taxes				(2)
Income (loss) from discontinued operations, net of taxes				$ (2)