Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Numerator:
Net income	$ 251,993	$ 265,065	$ 541,924	$ 383,583
Preferred stock dividends	4,628	4,274	9,281	8,337
Net income attributable to SLM Corporation common stock	247,365	260,791	532,643	375,246
Net income attributable to SLM Corporation common stock	$ 247,365	$ 260,791	$ 532,643	$ 375,246
Denominator:
Weighted average shares used to compute basic EPS (in shares)	218,924	235,061	219,670	238,261
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)	3,543	2,531	3,486	2,293
Weighted average shares used to compute diluted EPS (in shares)	222,467	237,592	223,156	240,554
Basic earnings per common share (in dollars per share)	$ 1.13	$ 1.11	$ 2.42	$ 1.57
Diluted earnings per common share (in dollars per share)	$ 1.11	$ 1.10	$ 2.39	$ 1.56
Antidilutive securities excluded from computation of earnings per share (less than) (in shares)	1,000	1,000	1,000	1,000