Acquisitions and Discontinued Operations - Change in Fair Values of Level 3 Portfolio Loans Held for Sale, Portfolio Loans, and Consolidated Education Loan Securitization Trusts (Parenthetical) (Detail) - USD ($)	Sep. 30, 2015	Sep. 30, 2014
Education Lending [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Issuances transfers	$ 0	$ 0