Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator:
Net income	$ 342,073	$ 140,201	$ 470,885	$ 781,408
Preferred stock dividends	1,757	1,192	3,032	2,393
Net income attributable to SLM Corporation common stock	340,316	139,009	467,853	779,015
Net income attributable to SLM Corporation common stock	$ 340,316	$ 139,009	$ 467,853	$ 779,015
Denominator:
Weighted average shares used to compute basic EPS (in shares)	261,333	312,183	269,112	336,478
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock, restricted stock units, performance stock units and Employee Stock Purchase Plan (“ESPP”) (in shares)	2,789	4,936	3,231	5,066
Weighted average shares used to compute diluted EPS (in shares)	264,122	317,119	272,343	341,544
Basic earnings per common share (in dollars per share)	$ 1.30	$ 0.45	$ 1.74	$ 2.32
Diluted earnings per common share (in dollars per share)	$ 1.29	$ 0.44	$ 1.72	$ 2.28
Antidilutive securities excluded from computation of earnings per share (in shares)	2,000	1,000	1,000	1,000