Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income attributable to SLM Corporation	$ 70,242	$ 56,965	$ 57,205	$ 65,915	$ 89,845	$ 45,724	$ 91,016	$ 47,699	$ 250,327	$ 274,284	$ 194,219
Preferred stock dividends	5,506	5,316	5,243	5,139	4,989	4,913	4,870	4,823	21,204	19,595	12,933
Net income attributable to SLM Corporation common stock	$ 64,736	$ 51,649	$ 51,962	$ 60,776	$ 84,856	$ 40,811	$ 86,146	$ 42,876	$ 229,123	$ 254,689	$ 181,286
Denominator:
Weighted average shares used to compute basic EPS (in shares)									427,876	425,574	423,970
Effect of dilutive securities:
Dilutive effect of stock options, restricted stock, restricted stock units and Employee Stock Purchase Plan (ESPP) (in shares)									5,043	6,660	8,299
Weighted average shares used to compute diluted EPS (in shares)									432,919	432,234	432,269
Basic earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.15	$ 0.12	$ 0.12	$ 0.14	$ 0.2	$ 0.1	$ 0.2	$ 0.1	$ 0.54	$ 0.60	$ 0.43
Diluted earnings per common share attributable to SLM Corporation (in dollars per share)	$ 0.15	$ 0.12	$ 0.12	$ 0.14	$ 0.2	$ 0.09	$ 0.2	$ 0.1	$ 0.53	$ 0.59	$ 0.42
Antidilutive securities excluded from computation of earnings per share (in shares)									1,000	2,000	3,000