Parent Only Statements - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 5,563,877	$ 2,559,106	$ 1,534,339
Tax indemnification receivable	27,558	39,207
Other assets	29,398	48,141
Total assets	32,686,479	26,638,173
Liabilities
Long-Term	4,354,037	4,284,304
Income taxes payable, net	0	0
Other liabilities	254,731	224,951
Total liabilities	29,374,643	23,665,517
Preferred stock, par value $0.20 per share, 20 million shares authorized:
Common stock, par value $0.20 per share, 1.125 billion shares authorized: 453.6 million and 449.9 million shares issued, respectively	90,720	89,972
Additional paid-in capital	1,307,630	1,274,635
Accumulated other comprehensive income (loss) (net of tax expense (benefit) of ($3,995) and $3,436, respectively)	(12,367)	10,623
Retained earnings	1,850,512	1,340,017
Total SLM Corporation stockholders’ equity before treasury stock	3,636,495	3,115,247
Less: Common stock held in treasury at cost: 32.5 million and 14.2 million shares, respectively	(324,659)	(142,591)
Total equity	3,311,836	2,972,656
Total liabilities and equity	32,686,479	26,638,173
Parent Company
Assets
Cash and cash equivalents	153,508	191,776	$ 260,255	$ 292,277
Total investments in subsidiaries (primarily Sallie Mae Bank)	3,326,578	2,963,949
Tax indemnification receivable	27,558	39,207
Due from subsidiaries, net	42,544	48,798
Other assets	2,579	2,246
Total assets	3,552,767	3,245,976
Liabilities
Long-Term	198,159	197,348
Income taxes payable, net	11,457	37,271
Payable due to Navient	9,064	9,480
Other liabilities	22,251	29,221
Total liabilities	240,931	273,320
Preferred stock, par value $0.20 per share, 20 million shares authorized:
Common stock, par value $0.20 per share, 1.125 billion shares authorized: 453.6 million and 449.9 million shares issued, respectively	90,720	89,972
Additional paid-in capital	1,307,630	1,274,635
Accumulated other comprehensive income (loss) (net of tax expense (benefit) of ($3,995) and $3,436, respectively)	(12,367)	10,623
Retained earnings	1,850,512	1,340,017
Total SLM Corporation stockholders’ equity before treasury stock	3,636,495	3,115,247
Less: Common stock held in treasury at cost: 32.5 million and 14.2 million shares, respectively	(324,659)	(142,591)
Total equity	3,311,836	2,972,656
Total liabilities and equity	3,552,767	3,245,976
Parent Company | Series B Preferred Stock
Preferred stock, par value $0.20 per share, 20 million shares authorized:
Preferred stock issued	$ 400,000	$ 400,000