Acquisition, Divestiture, and Discontinued Operations - Combined Results of Discontinued Operations (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income taxes	$ 1	$ 1	$ 3	$ 3
Income (loss) from discontinued operations, net of taxes	1	1	6	5
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	6	6	17	20
Provision for credit losses	5	1	8	3
Net interest income after provision for credit losses	1	5	9	17
Noninterest income	1	1	4	4
Noninterest expense	1	4	4	13
Income (loss) before income taxes	1	2	9	8
Income taxes	0	1	3	3
Income (loss) from discontinued operations, net of taxes	1	$ 1	$ 6	$ 5
Charges determined by applying a matched funds transfer pricing methodology to the liabilities assumed necessary to support the discontinued operations, after tax	$ 5