Acquisitions and Discontinued Operations - Components of Assets and Liabilities of Education Lending Business (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Unearned income on loans	$ 957	$ 1,388
Segment, discontinued operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Unearned income on loans	(5)	(2)
Segment, discontinued operations [Member] | Education lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Unearned income on loans	$ (5)	$ (2)