Parent Only Statements - Balance Sheets (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets
Cash and cash equivalents	$ 4,149,838	$ 4,616,117	$ 4,334,603
Tax indemnification receivable	0	2,816
Other assets	52,342	34,073
Total assets	29,169,468	28,811,029
Liabilities
Long-term borrowings	5,227,512	5,235,114
Other liabilities	407,971	400,874
Total liabilities	27,288,671	27,084,059
Equity
Common stock, par value $0.20 per share, 1.125 billion shares authorized: 438.2 million and 435.1 million shares issued, respectively	87,647	87,025
Additional paid-in capital	1,148,689	1,109,072
Accumulated other comprehensive loss (net of tax benefit of $(24,176) and $(30,160), respectively)	(75,104)	(93,870)
Retained earnings	3,624,859	3,163,640
Total SLM Corporation stockholders’ equity before treasury stock	5,037,161	4,516,937
Less: Common stock held in treasury at cost: 217.9 million and 194.4 million shares, respectively	(3,156,364)	(2,789,967)
Total equity	1,880,797	1,726,970	2,149,711	$ 2,562,835
Total liabilities and equity	$ 29,169,468	$ 28,811,029
Preferred stock, par or stated value (in dollars per share)	$ 0.20	$ 0.20
Preferred stock, shares authorized (in shares)	20.0	20.0
Preferred stock liquidation preference (in dollars per share)	$ 100	$ 100
Common stock, par value (in dollars per share)	$ 0.20	$ 0.20
Common stock, shares authorized (in shares)	1,125.0	1,125.0
Common stock, shares issued (in shares)	438.2	435.1
Accumulated other comprehensive income, tax	$ 24,176	$ 30,160
Common stock held in treasury (in shares)	217.9	194.4
Series B Preferred Stock
Equity
Preferred stock liquidation preference (in dollars per share)	$ 100
Parent Company
Assets
Cash and cash equivalents	$ 237,857	$ 196,820	$ 570,726	$ 539,074
Total investments in subsidiaries (primarily Sallie Mae Bank)	2,628,838	2,476,020
Tax indemnification receivable	0	2,816
Due from subsidiaries, net	63,679	100,543
Other assets	2,270	3,052
Total assets	2,932,644	2,779,251
Liabilities
Long-term borrowings	992,200	988,986
Income taxes payable, net	26,701	26,211
Other liabilities	32,946	37,084
Total liabilities	1,051,847	1,052,281
Equity
Common stock, par value $0.20 per share, 1.125 billion shares authorized: 438.2 million and 435.1 million shares issued, respectively	87,647	87,025
Additional paid-in capital	1,148,689	1,109,072
Accumulated other comprehensive loss (net of tax benefit of $(24,176) and $(30,160), respectively)	(75,104)	(93,870)
Retained earnings	3,624,859	3,163,640
Total SLM Corporation stockholders’ equity before treasury stock	5,037,161	4,516,937
Less: Common stock held in treasury at cost: 217.9 million and 194.4 million shares, respectively	(3,156,364)	(2,789,967)
Total equity	1,880,797	1,726,970
Total liabilities and equity	$ 2,932,644	$ 2,779,251
Preferred stock, par or stated value (in dollars per share)	$ 0.20	$ 0.20
Preferred stock, shares authorized (in shares)	20.0	20.0
Common stock, par value (in dollars per share)	$ 0.20	$ 0.20
Common stock, shares authorized (in shares)	1,125.0	1,125.0
Common stock, shares issued (in shares)	438.2	435.1
Accumulated other comprehensive income, tax	$ 24,176	$ (30,160)
Common stock held in treasury (in shares)	217.9	194.4
Parent Company | Series B Preferred Stock
Equity
Series B: 2.5 million and 2.5 million shares issued, respectively, at stated value of $100 per share	$ 251,070	$ 251,070
Preferred stock, shares issued (in shares)	2.5	2.5
Preferred stock liquidation preference (in dollars per share)	$ 100	$ 100