Earnings per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income	$ 56,965	$ 45,724	$ 180,085	$ 184,439
Preferred stock dividends	5,316	4,913	15,698	14,606
Net income attributable to SLM Corporation common stock	$ 51,649	$ 40,811	$ 164,387	$ 169,833
Denominator:
Weighted average shares used to compute basic EPS (in shares)	428,077	426,019	427,711	425,384
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)	5,446	6,528	4,368	7,147
Weighted average shares used to compute diluted EPS (in shares)	433,523	432,547	432,079	432,531
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.12	$ 0.10	$ 0.38	$ 0.40
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.12	$ 0.09	$ 0.38	$ 0.39
Securities excluded from computation of EPS (in shares)	1,000	2,000	1,000	2,000