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
	Mar. 31, 2014	Mar. 31, 2013
Portfolio Student Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	$ 147	$ 157
Gains (losses) recognized in earnings
Purchases
Sales
Settlements	(4)	(3)
Ending Balance	143	154
Trust Student Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	1,960	2,369
Gains (losses) recognized in earnings	2	43
Purchases
Sales
Settlements	(69)	(79)
Ending Balance	1,893	2,333
Trust Other Assets [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	20	26
Gains (losses) recognized in earnings
Purchases
Sales
Settlements	(1)	(1)
Ending Balance	19	25
Trust Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	1,834	2,159
Gains (losses) recognized in earnings	16	59
Purchases
Sales
Settlements	(54)	(92)
Ending Balance	1,796	2,126
Trust Other Liabilities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Beginning Balance	20	22
Gains (losses) recognized in earnings
Purchases
Sales
Settlements		3
Ending Balance	$ 20	$ 25