Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net income	$ 57,205	$ 91,016	$ 123,120	$ 138,715
Preferred stock dividends	5,243	4,870	10,382	9,693
Net income attributable to SLM Corporation common stock	$ 51,962	$ 86,146	$ 112,738	$ 129,022
Denominator:
Weighted average shares used to compute basic EPS (in shares)	427,942	425,688	427,526	425,061
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	3,854	7,054	3,823	7,462
Weighted average shares used to compute diluted EPS (in shares)	431,796	432,742	431,349	432,523
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.12	$ 0.20	$ 0.26	$ 0.30
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.12	$ 0.20	$ 0.26	$ 0.30
Securities excluded from computation of EPS (in shares)	1,000	2,000	4,000	2,000