Earnings (Loss) per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net income (loss)	$ (45,152)	$ 29,365	$ 496,772	$ 412,948
Preferred stock dividends	4,648	4,642	13,929	12,979
Net income (loss) attributable to SLM Corporation common stock	(49,800)	24,723	482,843	399,969
Net income (loss) attributable to SLM Corporation common stock	$ (49,800)	$ 24,723	$ 482,843	$ 399,969
Denominator:
Weighted average shares used to compute basic EPS (in shares)	214,873	226,120	218,059	234,170
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)	0	2,680	3,494	2,423
Weighted average shares used to compute diluted EPS (in shares)	214,873	228,800	221,553	236,593
Basic earnings per common share (in dollars per share)	$ (0.23)	$ 0.11	$ 2.21	$ 1.71
Diluted earnings per common share (in dollars per share)	$ (0.23)	$ 0.11	$ 2.18	$ 1.69
Antidilutive securities excluded from computation of earnings per share (less than) (in shares)	6,000	1,000	1,000	1,000