Parent Only Statements - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Nov. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	$ 4,334,603	$ 4,455,292		$ 5,563,877
Income taxes receivable, net	239,578	374,706
Tax indemnification receivable	8,047	18,492
Other assets	26,351	19,533
Total assets	29,221,899	30,770,423
Liabilities
Long-term borrowings	5,930,990	5,189,217
Other liabilities	313,074	352,332
Total liabilities	27,072,188	28,207,588
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: 432.0 million and 456.7 million shares issued, respectively	86,403	91,346
Additional paid-in capital	1,074,384	1,331,247
Accumulated other comprehensive loss (net of tax benefit of $(5,707) and $(10,908), respectively)	(17,897)	(34,200)
Retained earnings	2,817,134	1,722,365		1,850,512
Total SLM Corporation stockholders’ equity before treasury stock	4,211,094	3,361,828
Less: Common stock held in treasury at cost: 153.1 million and 81.4 million shares, respectively	(2,061,383)	(798,993)
Total equity	2,149,711	2,562,835
Total liabilities and equity	29,221,899	30,770,423
Series B Preferred Stock
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: 432.0 million and 456.7 million shares issued, respectively			$ 68,000
Parent Company
Assets
Cash and cash equivalents	570,726	539,074		$ 153,508	$ 191,776
Total investments in subsidiaries (primarily Sallie Mae Bank)	2,527,780	2,689,027
Income taxes receivable, net	0	1,835
Tax indemnification receivable	8,047	18,492
Due from subsidiaries, net	105,667	47,357
Other assets	3,361	2,457
Total assets	3,215,581	3,298,242
Liabilities
Long-term borrowings	986,138	692,879
Income taxes payable, net	34,822	0
Payable due to Navient	101	8,531
Other liabilities	44,809	33,997
Total liabilities	1,065,870	735,407
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: 432.0 million and 456.7 million shares issued, respectively	86,403	91,346
Additional paid-in capital	1,074,384	1,331,247
Accumulated other comprehensive loss (net of tax benefit of $(5,707) and $(10,908), respectively)	(17,897)	(34,200)
Retained earnings	2,817,134	1,722,365
Total SLM Corporation stockholders’ equity before treasury stock	4,211,094	3,361,828
Less: Common stock held in treasury at cost: 153.1 million and 81.4 million shares, respectively	(2,061,383)	(798,993)
Total equity	2,149,711	2,562,835
Total liabilities and equity	3,215,581	3,298,242
Parent Company | Series B Preferred Stock
Preferred stock, par value $0.20 per share, 20 million shares authorized:
Preferred stock issued	$ 251,070	$ 251,070