Earnings Per Common Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net income attributable to SLM Corporation	$ 19,717	$ 82,926	$ 44,128	$ 47,448	$ 60,202	$ 49,390	$ 76,469	$ 72,885	$ 194,219	$ 258,945	$ 217,620
Preferred stock dividends	4,855	4,850	3,228	0	0	0	0	0	12,933	0	0
Net income attributable to SLM Corporation common stock	$ 14,862	$ 78,076	$ 40,900	$ 47,448	$ 60,202	$ 49,390	$ 76,469	$ 72,885	$ 181,286	$ 258,945	$ 217,620
Denominator:
Weighted average shares used to compute basic EPS (in shares)									423,970,000	440,108,000	476,118,000
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock, restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)									8,299,000	8,441,000	6,774,000
Weighted average shares used to compute diluted EPS (in shares)									432,269,000	448,549,000	482,892,000
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.04	$ 0.18	$ 0.10	$ 0.11	$ 0.14	$ 0.11	$ 0.17	$ 0.16	$ 0.43	$ 0.59	$ 0.46
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.03	$ 0.18	$ 0.09	$ 0.11	$ 0.14	$ 0.11	$ 0.17	$ 0.16	$ 0.42	$ 0.58	$ 0.45
Antidilutive securities excluded from computation of earnings per share									3,000,000	3,000,000	12,000,000