CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Treasury Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Series A Preferred Stock	Retained Earnings Series B Preferred Stock	Total SLM Corporation Equity	Total SLM Corporation Equity Series A Preferred Stock	Total SLM Corporation Equity Series B Preferred Stock
Beginning Balance (in shares) at Dec. 31, 2014		7,300,000	423,438,848	(1,365,277)
Beginning Balance, shares issued (in shares) at Dec. 31, 2014			424,804,125
Beginning Balance at Dec. 31, 2014		$ 565,000	$ 84,961	$ (12,187)	$ 1,090,511	$ (11,393)	$ 113,066			$ 1,829,958
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 138,715						138,715			138,715
Other comprehensive loss, net of tax	$ (55)					(55)				(55)
Total comprehensive income										138,660
Cash dividends:
Cash dividends, preferred stock								$ (5,750)	$ (3,943)		$ (5,750)	$ (3,943)
Dividend equivalent units related to employee stock-based compensation plans					1,121		(1,121)			0
Issuance of common shares (in shares)	5,208,074		5,208,074
Issuance of common shares			$ 1,042		12,307					13,349
Tax benefit related to employee stock-based compensation					5,774					5,774
Stock-based compensation expense					11,210					11,210
Shares repurchased related to employee stock-based compensation plans (in shares)			(2,764,093)	(2,764,093)
Shares repurchased related to employee stock-based compensation plans				$ (27,085)						(27,085)
Ending Balance (in shares) at Jun. 30, 2015		7,300,000	425,882,829	(4,129,370)
Ending Balance, shares issued (in shares) at Jun. 30, 2015			430,012,199
Ending Balance at Jun. 30, 2015		$ 565,000	$ 86,003	$ (39,272)	1,120,923	(11,448)	240,967			1,962,173
Beginning Balance (in shares) at Dec. 31, 2015		7,300,000	426,303,244	(4,374,190)
Beginning Balance, shares issued (in shares) at Dec. 31, 2015			430,677,434
Beginning Balance at Dec. 31, 2015	$ 2,096,323	$ 565,000	$ 86,136	$ (41,223)	1,135,860	(16,059)	366,609			2,096,323
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	123,120						123,120			123,120
Other comprehensive loss, net of tax	$ (17,794)					(17,794)				(17,794)
Total comprehensive income										105,326
Cash dividends:
Cash dividends, preferred stock								$ (5,750)	$ (4,632)		$ (5,750)	$ (4,632)
Dividend equivalent units related to employee stock-based compensation plans					400		(400)			0
Issuance of common shares (in shares)	3,166,474		3,166,474
Issuance of common shares			$ 633		3,224					3,857
Tax benefit related to employee stock-based compensation					(2,249)					(2,249)
Stock-based compensation expense					12,548					12,548
Shares repurchased related to employee stock-based compensation plans (in shares)			(1,391,927)	(1,391,927)
Shares repurchased related to employee stock-based compensation plans				$ (8,512)						(8,512)
Ending Balance (in shares) at Jun. 30, 2016		7,300,000	428,077,791.000	(5,766,117.000)
Ending Balance, shares issued (in shares) at Jun. 30, 2016			433,843,908.000
Ending Balance at Jun. 30, 2016	$ 2,196,911	$ 565,000	$ 86,769	$ (49,735)	$ 1,149,783	$ (33,853)	$ 478,947			$ 2,196,911