CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Series A Preferred Stock	Total SLM Corporation Equity	Total SLM Corporation Equity Series A Preferred Stock	Total SLM Corporation Equity Series B Preferred Stock	Redemption of Series A Preferred Stock	Redemption of Series A Preferred Stock Series A 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
Beginning balance, shares issued (in shares) at Dec. 31, 2016						7,300,000		436,632,479
Beginning balance (in shares) at Dec. 31, 2016								428,903,559	(7,728,920)
Beginning balance at Dec. 31, 2016			$ 2,347,058			$ 565,000		$ 87,327	$ (67,484)	$ 1,175,564	$ (8,671)	$ 595,322
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 288,934		288,934									288,934
Other comprehensive income, net of tax	11,419		11,419								11,419
Total comprehensive income	$ 300,353		300,353
Cash dividends:
Preferred Stock, series B ($3.91 per share)				$ (3,961)	$ (11,753)								$ (3,961)	$ (11,753)
Redemption of Series A Preferred Stock (in shares)	(3,358,417)						(3,300,000)
Redemption of Series A Preferred Stock		$ (165,000)					$ (165,000)
Dividend equivalent units related to employee stock-based compensation plans			0							96		(96)
Issuance of common shares (in shares)	6,831,108							6,831,108
Issuance of common shares			19,655					$ 1,366		18,289
Stock-based compensation expense			27,899							27,899
Common stock repurchased (in shares)	0
Shares repurchased related to employee stock-based compensation plans (in shares)								(3,358,417)	(3,358,417)
Shares repurchased related to employee stock-based compensation plans			(40,160)						$ (40,160)
Ending balance, shares issued (in shares) at Dec. 31, 2017						4,000,000		443,463,587
Ending balance (in shares) at Dec. 31, 2017								432,376,250	(11,087,337)
Ending balance at Dec. 31, 2017			2,474,256			$ 400,000		$ 88,693	$ (107,644)	1,222,277	2,748	868,182
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification resulting from the adoption of ASU No. 2018-02	$ 600
Beginning balance, shares issued (in shares) at Dec. 31, 2017						4,000,000		443,463,587
Beginning balance (in shares) at Dec. 31, 2017								432,376,250	(11,087,337)
Beginning balance at Dec. 31, 2017			2,474,256			$ 400,000		$ 88,693	$ (107,644)	1,222,277	2,748	868,182
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	487,476		487,476									487,476
Other comprehensive income, net of tax	7,013		7,013								7,013
Total comprehensive income	$ 494,489		494,489
Reclassification resulting from the adoption of ASU No. 2018-02			0							0	592	(592)
Cash dividends:
Preferred Stock, series B ($3.91 per share)				$ (15,640)									$ (15,640)
Redemption of Series A Preferred Stock (in shares)	(3,087,396)
Issuance of common shares (in shares)	6,392,634							6,392,634
Issuance of common shares			22,113					$ 1,279		20,834
Stock-based compensation expense			31,524							31,524
Common stock repurchased (in shares)	0
Shares repurchased related to employee stock-based compensation plans (in shares)								(3,087,396)	(3,087,396)
Shares repurchased related to employee stock-based compensation plans			(34,947)						$ (34,947)
Ending balance, shares issued (in shares) at Dec. 31, 2018						4,000,000		449,856,221
Ending balance (in shares) at Dec. 31, 2018								435,681,488	(14,174,733)
Ending balance at Dec. 31, 2018	$ 2,972,656		2,972,656			$ 400,000		$ 89,972	$ (142,591)	1,274,635	10,623	1,340,017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification resulting from the adoption of ASU No. 2017-12 | Accounting Standards Update 2017-12	861										270	591
Net income	578,276		578,276									578,276
Other comprehensive income, net of tax	(22,990)		(22,990)								(22,990)
Total comprehensive income	$ 555,286		555,286
Cash dividends:
Preferred Stock, series B ($3.91 per share)			(16,837)									(16,837)
Common Stock ($0.12 per share)			(51,114)									(51,114)
Redemption of Series A Preferred Stock (in shares)	(1,369,630)
Dividend equivalent units related to employee stock-based compensation plans			0							5		(5)
Issuance of common shares (in shares)	3,743,705							3,743,705
Issuance of common shares			3,375					$ 748		2,627
Stock-based compensation expense			30,538							30,363		175
Common stock repurchased (in shares)	(16,962,199)							(16,962,199)	(16,962,199)
Common stock repurchased	$ (33,000)		(167,201)						$ (167,201)
Shares repurchased related to employee stock-based compensation plans (in shares)								(1,369,630)	(1,369,630)
Shares repurchased related to employee stock-based compensation plans			(14,867)						$ (14,867)
Ending balance, shares issued (in shares) at Dec. 31, 2019						4,000,000		453,599,926
Ending balance (in shares) at Dec. 31, 2019								421,093,364	(32,506,562)
Ending balance at Dec. 31, 2019	$ 3,311,836		$ 3,311,836			$ 400,000		$ 90,720	$ (324,659)	$ 1,307,630	$ (12,367)	$ 1,850,512