CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income:
Loans	$ 2,249,169	$ 1,894,687	$ 1,413,505
Investments	7,607	6,162	8,288
Cash and cash equivalents	74,256	34,503	15,510
Total interest income	2,331,032	1,935,352	1,437,303
Interest expense:
Deposits	547,746	389,349	223,691
Interest expense on short-term borrowings	6,193	5,833	6,341
Interest expense on long-term borrowings	153,778	127,106	78,050
Total interest expense	707,717	522,288	308,082
Net interest income	1,623,315	1,413,064	1,129,221
Less: provisions for credit losses	354,249	244,864	185,765
Net interest income after provisions for credit losses	1,269,066	1,168,200	943,456
Non-interest income (loss):
Gains on sales of loans, net	0	2,060	0
Losses on sales of securities, net	0	(1,549)	0
Gains (losses) on derivatives and hedging activities, net	17,825	(87)	(8,266)
Other income (loss)	31,102	(52,319)	5,364
Total non-interest income (loss)	48,927	(51,895)	(2,902)
Non-interest expenses:
Compensation and benefits	278,229	252,346	213,319
FDIC assessment fees	32,852	32,786	28,950
Other operating expenses	263,172	271,844	206,820
Total non-interest expenses	574,253	556,976	449,089
Income before income tax expense	743,740	559,329	491,465
Income tax expense	165,464	71,853	202,531
Net income	578,276	487,476	288,934
Preferred stock dividends	16,837	15,640	15,714
Net income attributable to SLM Corporation common stock	$ 561,439	$ 471,836	$ 273,220
Basic earnings per common share attributable to SLM Corporation (in usd per share)	$ 1.31	$ 1.08	$ 0.63
Average common shares outstanding (in shares)	427,292	435,054	431,216
Diluted earnings per common share attributable to SLM Corporation (in usd per share)	$ 1.30	$ 1.07	$ 0.62
Average common and common equivalent shares outstanding (in shares)	430,674	439,681	438,551
Declared dividends per common share attributable to SLM Corporation (in usd per share)	$ 0.12	$ 0	$ 0