Acquisitions and Discontinued Operations - Consolidated Trusts' Assets and Liabilities at Fair Value and Contractual Values (Detail) (Segment, Discontinued Operations [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Education Lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Trust loans accounted for at fair value	$ 68	$ 87	$ 101
Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Trust loans accounted for at fair value	2,513	2,726	2,829
Trust fair value of securities	2,310	2,522	2,623
Trust [Member] | Education Lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio contractual amount of loans	68
Trust contractual amount of loans	2,617
Trust contractual amount of other assets	29
Trust contractual amount of securities	2,665
Trust contractual amount of other liabilities	25
Portfolio fair value of loans	71
Trust loans accounted for at fair value	2,513	2,726	2,829
Trust fair value of other assets	29
Trust fair value of securities	2,310	2,522	2,623
Trust fair value of other liabilities	$ 25