Earnings per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Numerator:
Net income	$ 94,943	$ 65,915
Preferred stock dividends	5,575	5,139
Net income attributable to SLM Corporation common stock	$ 89,368	$ 60,776
Denominator:
Weighted average shares used to compute basic EPS (in shares)	429,891,000	427,111,000
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	8,844,000	3,792,000
Weighted average shares used to compute diluted EPS (in shares)	438,735,000	430,903,000
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.21	$ 0.14
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.20	$ 0.14
Securities excluded from computation of EPS (in shares)	0	6,000,000