CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income:
Loans	$ 1,989,004	$ 2,249,169	$ 1,894,687
Investments	11,743	7,607	6,162
Cash and cash equivalents	20,913	74,256	34,503
Total interest income	2,021,660	2,331,032	1,935,352
Interest expense:
Deposits	393,194	547,746	389,349
Interest expense on short-term borrowings	14,459	6,193	5,833
Interest expense on long-term borrowings	134,014	153,778	127,106
Total interest expense	541,667	707,717	522,288
Net interest income	1,479,993	1,623,315	1,413,064
Less: provisions for credit losses	93,133	354,249	244,864
Net interest income after provisions for credit losses	1,386,860	1,269,066	1,168,200
Non-interest income (loss):
Gains on sales of loans, net	238,315	0	2,060
Losses on sales of securities, net	0	0	(1,549)
Gains (losses) on derivatives and hedging activities, net	49,544	17,825	(87)
Other income (loss)	43,590	31,102	(52,319)
Total non-interest income (loss)	331,449	48,927	(51,895)
Operating expenses
Compensation and benefits	282,497	278,229	252,346
FDIC assessment fees	21,956	32,852	32,786
Other operating expenses	233,635	263,172	271,844
Total operating expenses	538,088	574,253	556,976
Restructuring expenses	26,215	0	0
Total non-interest expenses	564,303	574,253	556,976
Income before income tax expense	1,154,006	743,740	559,329
Income tax expense	273,316	165,464	71,853
Net income	880,690	578,276	487,476
Preferred stock dividends	9,734	16,837	15,640
Net income attributable to SLM Corporation common stock	$ 870,956	$ 561,439	$ 471,836
Basic earnings per common share attributable to SLM Corporation (in usd per share)	$ 2.27	$ 1.31	$ 1.08
Average common shares outstanding (in shares)	383,705	427,292	435,054
Diluted earnings per common share attributable to SLM Corporation (in usd per share)	$ 2.25	$ 1.30	$ 1.07
Average common and common equivalent shares outstanding (in shares)	387,195	430,674	439,681
Declared dividends per common share attributable to SLM Corporation (in usd per share)	$ 0.12	$ 0.12	$ 0