CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Interest income:
Loans	$ 1,914,554,000	$ 1,756,945,000	$ 1,989,004,000
Investments	35,304,000	13,859,000	11,743,000
Cash and cash equivalents	81,722,000	6,040,000	20,913,000
Total interest income	2,031,580,000	1,776,844,000	2,021,660,000
Interest expense:
Deposits	368,914,000	225,370,000	393,194,000
Interest expense on short-term borrowings	11,956,000	18,945,000	14,459,000
Interest expense on long-term borrowings	161,929,000	137,763,000	134,014,000
Total interest expense	542,799,000	382,078,000	541,667,000
Net interest income	1,488,781,000	1,394,766,000	1,479,993,000
Provisions for credit losses	633,453,000	(32,957,000)	93,133,000
Net interest income (loss) after provisions for credit losses	855,328,000	1,427,723,000	1,386,860,000
Non-interest income:
Gains on sales of loans, net	327,750,000	548,315,000	238,315,000
Gains (losses) on securities, net	(60,267,000)	39,096,000	4,372,000
Gains (losses) on derivatives and hedging activities, net	(5,000)	144,000	49,544,000
Other income	67,160,000	44,894,000	39,218,000
Total non-interest income	334,638,000	632,449,000	331,449,000
Operating expenses:
Compensation and benefits	270,354,000	258,321,000	282,497,000
FDIC assessment fees	20,939,000	23,368,000	21,956,000
Other operating expenses	260,169,000	236,964,000	233,635,000
Total operating expenses	551,462,000	518,653,000	538,088,000
Acquired intangible assets amortization expense	7,779,000	0	0
Restructuring expenses	0	1,255,000	26,215,000
Total non-interest expenses	559,241,000	519,908,000	564,303,000
Income before income tax expense	630,725,000	1,540,264,000	1,154,006,000
Income tax expense	161,711,000	379,751,000	273,316,000
Net income	469,014,000	1,160,513,000	880,690,000
Preferred stock dividends	9,029,000	4,736,000	9,734,000
Net income attributable to SLM Corporation common stock	$ 459,985,000	$ 1,155,777,000	$ 870,956,000
Basic earnings per common share (in usd per share)	$ 1.78	$ 3.67	$ 2.27
Average common shares outstanding (in shares)	258,439	314,993	383,705
Diluted earnings per common share (in usd per share)	$ 1.76	$ 3.61	$ 2.25
Average common and common equivalent shares outstanding (in shares)	261,503	319,912	387,195
Declared dividends per common share (in usd per share)	$ 0.44	$ 0.20	$ 0.12