Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net income attributable to SLM Corporation	$ 65,915	$ 47,699
Preferred stock dividends	5,139	4,823
Net income attributable to SLM Corporation common stock	$ 60,776	$ 42,876
Denominator:
Weighted average shares used to compute basic EPS (in shares)	427,111	424,428
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	3,792	7,874
Weighted average shares used to compute diluted EPS (in shares)	430,903	432,302
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.14	$ 0.10
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.14	$ 0.10
Securities excluded from computation of EPS (in shares)	6,000	2,000