Parent Only Statements - Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Condensed Income Statements, Captions [Line Items]
Interest income									$ 2,592,303	$ 2,031,580	$ 1,776,844
Interest expense									1,030,090	542,799	382,078
Net interest loss	$ 385,886	$ 384,628	$ 386,631	$ 405,068	$ 381,431	$ 369,510	$ 362,808	$ 375,032	1,562,213	1,488,781	1,394,766
Non-interest expenses									685,570	559,241	519,908
Income tax expense (benefit)	56,843	11,242	91,482	37,338	(19,492)	29,551	114,296	37,356	196,905	161,711	379,751
Net income									581,391	469,014	1,160,513
Preferred stock dividends	4,726	4,642	4,274	4,063	3,466	2,531	1,757	1,275	17,705	9,029	4,736
Net income attributable to SLM Corporation common stock	$ 163,717	$ 24,723	$ 260,791	$ 114,455	$ (80,509)	$ 72,641	$ 340,316	$ 127,537	563,686	459,985	1,155,777
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest income									9,334	4,084	392
Interest expense									39,850	39,860	35,208
Net interest loss									(30,516)	(35,776)	(34,816)
Non-interest loss									(2,701)	(5,117)	(13,078)
Non-interest expenses									61,958	55,466	54,352
Loss before income tax benefit and equity in net income from subsidiaries									(95,175)	(96,359)	(102,246)
Income tax expense (benefit)									(6,942)	(10,351)	8,477
Equity in net income from subsidiaries (primarily Sallie Mae Bank)									669,624	555,022	1,271,236
Net income									581,391	469,014	1,160,513
Preferred stock dividends									17,705	9,029	4,736
Net income attributable to SLM Corporation common stock									$ 563,686	$ 459,985	$ 1,155,777