Acquisitions and Discontinued Operations - Components of Income (Loss) from Discontinued Operations, Net of Taxes for Education Lending Business (Parenthetical) (Detail) (Segment, Discontinued Operations [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Charges determined by applying a matched funds transfer pricing methodology to the liabilities assumed necessary to support the discontinued operations, after tax	$ 32	$ 40	$ 50
Education Lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Charges determined by applying a matched funds transfer pricing methodology to the liabilities assumed necessary to support the discontinued operations, after tax	$ 32	$ 40	$ 50