Acquisitions and Discontinued Operations - Consolidated Trusts' Assets and Liabilities at Fair Value and Contractual Values (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Trust loans accounted for at fair value	$ 143	$ 147	$ 154
Segment, Discontinued Operations [Member] | Education Lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio fair value of loans	143	147	154
Segment, Discontinued Operations [Member] | Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Trust loans accounted for at fair value	1,893	1,960	2,333
Trust fair value of securities	1,796	1,834	2,126
Segment, Discontinued Operations [Member] | 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	136	140	148
Trust contractual amount of loans	1,889	1,964	2,357
Trust contractual amount of other assets	19	20	25
Trust contractual amount of securities	1,904	1,958	2,382
Trust contractual amount of other liabilities	20	20	25
Portfolio fair value of loans	143	147	154
Trust loans accounted for at fair value	1,893	1,960	2,333
Trust fair value of other assets	19	20	25
Trust fair value of securities	1,796	1,834	2,126
Trust fair value of other liabilities	$ 20	$ 20	$ 25