Acquisition, Divestiture, and Discontinued Operations - Change in Fair Values of Level 3 Portfolio Loans Held for Sale, Portfolio Loans, and Consolidated Education Loan Securitization Trusts (Details) - Discontinued Operations [Member] - Education Lending [Member] - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Purchases, sales, issuances, gains (losses) recognized in earnings	$ 0	$ 0	$ 0	$ 0
Portfolio Student Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,000,000	3,000,000	3,000,000	4,000,000
Settlements	0	0	(1,000,000)	(1,000,000)
Ending Balance	$ 2,000,000	$ 3,000,000	$ 2,000,000	$ 3,000,000