Acquisition, Divestiture, and Discontinued Operations - Components of Income (Loss) from Discontinued Operations, Net of Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income taxes	$ 1	$ 1	$ (23)
Income (loss) from discontinued operations, net of taxes	1	1	(39)
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	26	36	89
Provision for credit losses	13	21	21
Net interest income after provision for credit losses	13	15	68
Noninterest income	6	4	(101)
Noninterest expense	17	17	29
Income (loss) before income taxes	2	2	(62)
Income taxes	1	1	(23)
Income (loss) from discontinued operations, net of taxes	1	1	(39)
Charges determined by applying a matched funds transfer pricing methodology to the liabilities assumed necessary to support the discontinued operations, after tax	24	23	32
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	0	0	12
Noninterest income	0	0	10
Noninterest expense	0	0	1
Income (loss) before income taxes	0	0	21
Income taxes	0	0	8
Income (loss) from discontinued operations, net of taxes	0	0	13
Discontinued Operations [Member] | Austin Capital Management [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Noninterest expense	0	0	4
Income (loss) before income taxes	0	0	(4)
Income taxes	0	0	(1)
Income (loss) from discontinued operations, net of taxes	$ 0	$ 0	$ (3)