Acquisitions and Discontinued Operations - Combined Assets and Liabilities of Discontinued Operations (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Unearned income on loans	$ 980	$ 1,388	$ 1,413
Segment, Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Unearned income on loans	$ (2)	$ (2)	$ 1