Earnings (Loss) per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income (loss)	$ (85,211)	$ 150,277	$ 276,962	$ 308,466
Preferred stock dividends	2,478	4,331	5,942	8,799
Net income (loss) attributable to SLM Corporation common stock	$ (87,689)	$ 145,946	$ 271,020	$ 299,667
Denominator:
Weighted average shares used to compute basic EPS (in shares)	375,009,000	429,278,000	392,397,000	431,911,000
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	0	2,975,000	2,794,000	3,322,000
Weighted average shares used to compute diluted EPS (in shares)	375,009,000	432,253,000	395,191,000	435,233,000
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ (0.23)	$ 0.34	$ 0.69	$ 0.69
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ (0.23)	$ 0.34	$ 0.69	$ 0.69
Antidilutive securities excluded from computation of earnings per share (in shares)	7,000,000	1,000,000	3,000,000	1,000,000