CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($)	Total	Series A Preferred Stock	Series B Preferred Stock	Navient's subsidiary investment	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	Non-controlling interest
Beginning Balance (in shares) at Dec. 31, 2013					0	0	0
Beginning Balance, shares issued (in shares) at Dec. 31, 2013						0
Beginning Balance at Dec. 31, 2013	$ 1,166,143,000			$ 1,164,495,000	$ 0	$ 0	$ 0	$ 0	$ (3,024,000)	$ 0			$ 1,161,471,000			$ 4,672,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	174,068,000			68,173,000						106,329,000			174,502,000			(434,000)
Other comprehensive income (loss), net of tax	1,172,000								1,172,000				1,172,000
Comprehensive income	175,240,000												175,674,000			(434,000)
Net transfers (to) from affiliate	479,409,000			479,409,000									479,409,000
Separation adjustments related to Spin-Off of Navient Corporation (in shares)					7,300,000	422,790,320
Separation adjustments related to Spin-Off of Navient Corporation	0			(1,712,077,000)	$ 565,000,000	$ 84,558,000		1,062,519,000
Sale of non-controlling interest	(4,238,000)															(4,238,000)
Cash dividends:
Cash dividends, preferred stock		$ (4,792,000)	$ (3,286,000)								$ (4,792,000)	$ (3,286,000)		$ (4,792,000)	$ (3,286,000)
Dividend equivalent units related to employee stock-based compensation plans	$ 0							41,000		(41,000)
Issuance of common shares (in shares)	1,089,716					1,089,716
Issuance of common shares	$ 4,610,000					$ 219,000		4,391,000					4,610,000
Stock-based compensation expense	11,550,000							11,550,000					11,550,000
Shares repurchased related to employee stock-based compensation plans (in shares)						(715,393)	(715,393)
Shares repurchased related to employee stock-based compensation plans	(6,208,000)						$ (6,208,000)						(6,208,000)
Ending Balance (in shares) at Sep. 30, 2014					7,300,000	423,164,643	(715,393)
Ending Balance, shares issued (in shares) at Sep. 30, 2014						423,880,036
Ending Balance at Sep. 30, 2014	1,818,428,000			$ 0	$ 565,000,000	$ 84,777,000	$ (6,208,000)	1,078,501,000	(1,852,000)	98,210,000			1,818,428,000			$ 0
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	1,829,958,000				$ 565,000,000	$ 84,961,000	$ (12,187,000)	1,090,511,000	(11,393,000)	113,066,000			1,829,958,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	184,439,000									184,439,000			184,439,000
Other comprehensive income (loss), net of tax	(12,122,000)								(12,122,000)				(12,122,000)
Comprehensive income	172,317,000												172,317,000
Net transfers (to) from affiliate	$ 0
Cash dividends:
Cash dividends, preferred stock											$ (8,625,000)	$ (5,981,000)		$ (8,625,000)	$ (5,981,000)
Dividend equivalent units related to employee stock-based compensation plans								1,138,000		(1,138,000)			0
Issuance of common shares (in shares)	5,569,853					5,569,853
Issuance of common shares						$ 1,114,000		14,329,000					15,443,000
Tax benefit related to employee stock-based compensation								6,093,000					6,093,000
Stock-based compensation expense								16,423,000					16,423,000
Shares repurchased related to employee stock-based compensation plans (in shares)						(2,900,266)	(2,900,266)
Shares repurchased related to employee stock-based compensation plans							$ (28,294,000)						(28,294,000)
Ending Balance (in shares) at Sep. 30, 2015					7,300,000	426,108,435	(4,265,543)
Ending Balance, shares issued (in shares) at Sep. 30, 2015						430,373,978
Ending Balance at Sep. 30, 2015	$ 1,997,334,000				$ 565,000,000	$ 86,075,000	$ (40,481,000)	$ 1,128,494,000	$ (23,515,000)	$ 281,761,000			$ 1,997,334,000