Acquisitions and Discontinued Operations - Components of Income (Loss) from Discontinued Operations, Net of Taxes for Education Lending Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income taxes	$ 3	$ 2
Income (loss) from discontinued operations, net of taxes	5	4
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	10	24
Provision for credit losses	2	4
Net interest income after provision for credit losses	8	20
Noninterest income	4	(4)
Noninterest expense	4	10
Income (loss) before income taxes	8	6
Income taxes	3	2
Income (loss) from discontinued operations, net of taxes	5	4
Education Lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) before income taxes	8	(1)
Income taxes	3
Income (loss) from discontinued operations, net of taxes	5	(1)
Education Lending [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	10	23
Provision for credit losses	2	4
Net interest income after provision for credit losses	8	19
Noninterest income	4	(14)
Noninterest expense	$ 4	$ 6