Parent Only Statements - Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Condensed Income Statements, Captions [Line Items]
Interest income	$ 2,619,046	$ 2,592,303	$ 2,031,580
Interest expense	1,138,264	1,030,090	542,799
Net interest loss	1,480,782	1,562,213	1,488,781
Non-interest expenses	641,899	685,570	559,241
Income tax benefit	190,311	196,905	161,711
Net income	608,325	581,391	469,014
Preferred stock dividends	18,296	17,705	9,029
Net income attributable to SLM Corporation common stock	590,029	563,686	459,985
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest income	11,660	9,334	4,084
Interest expense	39,855	39,850	39,860
Net interest loss	(28,195)	(30,516)	(35,776)
Non-interest income (loss)	114	(2,701)	(5,117)
Non-interest expenses	62,696	61,958	55,466
Loss before income tax benefit and equity in net income from subsidiaries	(90,777)	(95,175)	(96,359)
Income tax benefit	(7,117)	(6,942)	(10,351)
Equity in net income from subsidiaries (primarily Sallie Mae Bank)	691,985	669,624	555,022
Net income	608,325	581,391	469,014
Preferred stock dividends	18,296	17,705	9,029
Net income attributable to SLM Corporation common stock	$ 590,029	$ 563,686	$ 459,985