Acquisitions and Discontinued Operations - Change in Fair Values of Level 3 Consolidated Education Loan Securitization Trusts and Portfolio Loans (Detail) (Segment, Discontinued Operations [Member], Education Lending [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Portfolio Student Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	$ 154	$ 157
Gains (losses) recognized in earnings
Settlements	(3)	(6)
Ending Balance	151	151
Trust Student Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	2,333	2,369
Gains (losses) recognized in earnings	68	111
Settlements	(84)	(163)
Ending Balance	2,317	2,317
Trust Other Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	25	26
Gains (losses) recognized in earnings
Settlements	(1)	(2)
Ending Balance	24	24
Trust Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	2,126	2,159
Gains (losses) recognized in earnings	85	144
Settlements	(93)	(185)
Ending Balance	2,118	2,118
Trust Other Liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	25	22
Gains (losses) recognized in earnings
Purchases
Sales
Issuances
Settlements	(4)	(1)
Ending Balance	$ 21	$ 21