Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net income	$ 608,325	$ 581,391	$ 469,014
Preferred stock dividends	18,296	17,705	9,029
Net income attributable to SLM Corporation common stock, diluted	590,029	563,686	459,985
Net income attributable to SLM Corporation common stock, basic	$ 590,029	$ 563,686	$ 459,985
Denominator:
Weighted average shares used to compute basic EPS (in shares)	216,220	231,411	258,439
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)	3,714	2,652	3,064
Weighted average shares used to compute diluted EPS (in shares)	219,934	234,063	261,503
Basic earnings per common share (in usd per share)	$ 2.73	$ 2.44	$ 1.78
Diluted earnings per common share (in usd per share)	$ 2.68	$ 2.41	$ 1.76
Antidilutive securities excluded from computation of earnings per share, less than (in shares)	1,000	1,000	1,000