Earnings per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Numerator [Abstract]
Net income attributable to SLM Corporation	$ 47,699		$ 47,448
Preferred stock dividends	4,823		0
Net income attributable to SLM Corporation common stock	$ 42,876		$ 47,448
Denominator [Abstract]
Weighted average shares used to compute basic EPS (in shares)	424,428,000		426,717,000
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock and restricted stock units (in shares)	7,874,000	[1],[2]	7,933,000	[1],[2]
Weighted average shares used to compute diluted EPS (in shares)	432,302,000		434,650,000
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.10		$ 0.11
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.10		$ 0.11
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,000,000		3,000,000

[1] For the three months ended March 31, 2015 and 2014, securities covering approximately 2 million and 3 million shares, respectively, were outstanding but not included in the computation of diluted earnings per share because they were anti-dilutive.

[2] Includes the potential dilutive effect of additional common shares that are issuable upon exercise of outstanding stock options, restricted stock, restricted stock units, and the outstanding commitment to issue shares under the ESPP, determined by the treasury stock method.