Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net income	$ 75,172	$ 72,840	$ 546,057	$ 854,248
Preferred stock dividends	2,531	1,166	5,563	3,559
Net income attributable to SLM Corporation common stock	72,641	71,674	540,494	850,689
Net income attributable to SLM Corporation common stock	$ 72,641	$ 71,674	$ 540,494	$ 850,689
Denominator:
Weighted average shares used to compute basic EPS (in shares)	251,266	299,890	263,098	324,148
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)	2,450	4,621	2,967	4,916
Weighted average shares used to compute diluted EPS (in shares)	253,716	304,511	266,065	329,064
Basic earnings per common share (in dollars per share)	$ 0.29	$ 0.24	$ 2.05	$ 2.62
Diluted earnings per common share (in dollars per share)	$ 0.29	$ 0.24	$ 2.03	$ 2.59
Antidilutive securities excluded from computation of earnings per share (in shares)	1,000	1,000	1,000	1,000