Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net income	$ 72,840	$ 171,028	$ 854,248	$ 447,990
Preferred stock dividends	1,166	2,058	3,559	8,000
Net income attributable to SLM Corporation common stock	71,674	168,970	850,689	439,990
Net income attributable to SLM Corporation common stock	$ 71,674	$ 168,970	$ 850,689	$ 439,990
Denominator:
Weighted average shares used to compute basic EPS (in shares)	299,890,000	375,094,000	324,148,000	386,587,000
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)	4,621,000	2,824,000	4,916,000	2,804,000
Weighted average shares used to compute diluted EPS (in shares)	304,511,000	377,918,000	329,064,000	389,391,000
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.24	$ 0.45	$ 2.62	$ 1.14
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.24	$ 0.45	$ 2.59	$ 1.13
Antidilutive securities excluded from computation of earnings per share (in shares)	1,000,000	2,000,000	1,000,000	0