Parent Only Statements - Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Income Statements, Captions [Line Items]
Interest income									$ 831,118	$ 674,294	$ 551,200
Interest expense									128,619	95,815	89,085
Net interest income	$ 187,846	$ 175,442	$ 168,257	$ 170,954	$ 150,676	$ 144,026	$ 144,539	$ 139,238	702,499	578,479	462,115
Other income	12,561	10,455	10,912	8,007	11,095	5,461	15,229	8,136	41,935	39,921	37,222
Operating expenses	85,245	92,864	89,799	81,187	78,724	72,079	60,479	63,671	349,095	274,881	270,474
Income tax expense	54,915	17,985	60,158	31,722	24,465	54,903	31,941	28,658	164,780	139,967	158,934
Net income					19,717	82,926	44,128	47,014	274,284	193,785	257,593
Preferred stock dividends	(4,989)	(4,913)	(4,870)	(4,823)	(4,855)	(4,850)	(3,228)	0	(19,595)	(12,933)	0
Net income attributable to SLM Corporation common stock	$ 84,856	$ 40,811	$ 86,146	$ 42,876	$ 14,862	$ 78,076	$ 40,900	$ 47,448	254,689	181,286	258,945
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest income									6,414	4,980	0
Interest expense									0	0	0
Net interest income									6,414	4,980	0
Other income									(239)	1,097	0
Operating expenses									36,141	36,967	3,556
Loss before income tax expense (benefit) and equity in net income from subsidiaries									(29,966)	(30,890)	(3,556)
Income tax expense									(8,612)	(13,196)	133,121
Equity in net income from subsidiaries (primarily Sallie Mae Bank)									295,638	211,479	394,270
Net income									274,284	193,785	257,593
Preferred stock dividends									19,595	12,933	0
Net income attributable to SLM Corporation common stock									$ 254,689	$ 180,852	$ 257,593