Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Numerator:
Net income	$ 128,812	$ 641,207
Preferred stock dividends	1,275	1,201
Net income attributable to SLM Corporation common stock	127,537	640,006
Net income attributable to SLM Corporation common stock	$ 127,537	$ 640,006
Denominator:
Weighted average shares used to compute basic EPS (in shares)	276,977	361,042
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)	3,677	5,198
Weighted average shares used to compute diluted EPS (in shares)	280,654	366,240
Basic earnings per common share (in dollars per share)	$ 0.46	$ 1.77
Diluted earnings per common share (in dollars per share)	$ 0.45	$ 1.75
Antidilutive securities excluded from computation of earnings per share (in shares)	3,000	1,000