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 (Detail) - Discontinued Operations [Member] - Education Lending [Member] - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Purchases, sales, issuances, gains (losses) recognized in earnings, transfers into Level 3 or out of Level 3	$ 0	$ 0
Portfolio Student Loans Held For Sale [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning of Period Balance	0	0
Gains (losses) recognized in earnings		(3,000,000)
Sales		(161,000,000)
Settlements	0	(11,000,000)
Loans transferred to held for sale		179,000,000
Loans transferred to portfolio		(4,000,000)
End of Period Balance	0	0
Portfolio Student Loans [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning of Period Balance	4,000,000	191,000,000
Gains (losses) recognized in earnings		1,000,000
Sales		0
Settlements	(1,000,000)	(13,000,000)
Loans transferred to held for sale		(179,000,000)
Loans transferred to portfolio		4,000,000
End of Period Balance	$ 3,000,000	$ 4,000,000