Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Numerator:
Net income	$ 304,540	$ 289,931
Preferred stock dividends	3,956	4,653
Net income attributable to SLM Corporation common stock	300,584	285,278
Net income attributable to SLM Corporation common stock	$ 300,584	$ 285,278
Denominator:
Weighted average shares used to compute basic EPS (in shares)	210,682	220,416
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)	4,304	3,429
Weighted average shares used to compute diluted EPS (in shares)	214,986	223,845
Basic earnings per common share (in dollars per share)	$ 1.43	$ 1.29
Diluted earnings per common share (in dollars per share)	$ 1.40	$ 1.27
Antidilutive securities excluded from computation of earnings per share (less than) (in shares)	1,000	2,000