Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Numerator:
Net income	$ 265,065	$ 342,073	$ 383,583	$ 470,885
Preferred stock dividends	4,274	1,757	8,337	3,032
Net income attributable to SLM Corporation common stock	260,791	340,316	375,246	467,853
Net income attributable to SLM Corporation common stock	$ 260,791	$ 340,316	$ 375,246	$ 467,853
Denominator:
Weighted average shares used to compute basic EPS (in shares)	235,061	261,333	238,261	269,112
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock, restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	2,531	2,789	2,293	3,231
Weighted average shares used to compute diluted EPS (in shares)	237,592	264,122	240,554	272,343
Basic earnings per common share (in dollars per share)	$ 1.11	$ 1.30	$ 1.57	$ 1.74
Diluted earnings per common share (in dollars per share)	$ 1.10	$ 1.29	$ 1.56	$ 1.72
Antidilutive securities excluded from computation of earnings per share (in shares)	1,000	2,000	1,000	1,000