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	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Portfolio Student Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	$ 151	$ 157
Gains (losses) recognized in earnings
Purchases
Sales
Issuances
Settlements	(3)	(9)
Ending Balance	148	148
Trust Student Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	2,317	2,369
Gains (losses) recognized in earnings	(105)	6
Purchases
Sales
Issuances
Settlements	(77)	(240)
Ending Balance	2,135	2,135
Trust Other Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	24	26
Gains (losses) recognized in earnings
Purchases
Sales
Issuances
Settlements	(1)	(3)
Ending Balance	23	23
Trust Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	2,118	2,159
Gains (losses) recognized in earnings	(14)	130
Purchases
Sales
Issuances
Settlements	(88)	(273)
Ending Balance	2,016	2,016
Trust Other Liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	21	22
Purchases
Sales
Issuances
Settlements		(1)
Ending Balance	$ 21	$ 21