Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator [Abstract]
Net income attributable to SLM Corporation	$ 91,016	$ 44,128	$ 138,715	$ 91,576
Preferred stock dividends	4,870	3,228	9,693	3,228
Net income attributable to SLM Corporation common stock	$ 86,146	$ 40,900	$ 129,022	$ 88,348
Denominator [Abstract]
Weighted average shares used to compute basic EPS (in shares)	425,688	422,805	425,061	424,751
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	7,054	7,945	7,462	7,938
Weighted average shares used to compute diluted EPS (in shares)	432,742	430,750	432,523	432,689
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.20	$ 0.10	$ 0.30	$ 0.21
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.20	$ 0.09	$ 0.30	$ 0.20
Securities excluded from computation of EPS (in shares)	2,000	4,000	2,000	3,000