Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net income	$ 153	$ 83	$ 281	$ 210
Adjustments to reconcile net income to net cash provided by operating activities:
(Gains) on sales of loans	(16)		(16)
(Gains) losses on debt repurchases	(44)	7	(59)	8
Goodwill and acquired intangible asset impairment and amortization expense	11	6	18	16
Stock-based compensation expense			17	18
Mark-to-market losses (gains) on derivative and hedging activities, net			173	(63)
Provisions for loan losses	68	112	144	199
Decrease (increase) in accrued interest receivable			22	(121)
(Decrease) increase in accrued interest payable			(29)	86
Decrease in other assets			148	160
Decrease in other liabilities			(177)	(31)
Total adjustments			241	272
Net cash provided by operating activities			522	482
Investing activities
Education loans acquired and originated			(1,970)	(1,555)
Principal payments on education loans			6,411	7,340
Proceeds from sales of education loans			408
Other investing activities, net			32	(29)
Net cash provided by investing activities			4,881	5,756
Financing activities
Borrowings collateralized by loans in trust - issued			4,863	5,443
Borrowings collateralized by loans in trust - repaid			(7,630)	(6,791)
Long-term notes issued				495
Long-term notes repaid			(937)	(1,443)
Other financing activities, net			(149)	(46)
Common stock repurchased			(233)
Common dividends paid			(76)	(85)
Net cash used in financing activities			(6,239)	(5,876)
Net (decrease) increase in cash, cash equivalents, restricted cash and restricted cash equivalents			(836)	362
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of period			5,262	4,646
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period	4,426	5,008	4,426	5,008
Cash disbursements made (refunds received) for:
Interest			1,845	1,618
Income taxes paid			22	24
Income taxes received			(1)	(2)
Reconciliation of the Consolidated Statements of Cash Flows to the Consolidated Balance Sheets:
Cash and cash equivalents	1,746	1,622	1,746	1,622
Restricted cash and restricted cash equivalents	2,680	3,386	2,680	3,386
Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period	$ 4,426	$ 5,008	4,426	5,008
Noncash activity:
Investing activity - Held-to-maturity asset backed securities retained related to sales of education loans			22
Operating activity - Servicing assets recognized upon sales of education loans			3
Asset-backed Securities, Securitized Loans and Receivables [Member]
Financing activities
Asset-backed commercial paper conduits, net			$ (2,077)	$ (3,449)