Parent Only Statements - Balance Sheets (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets
Cash and cash equivalents	$ 4,700,366	$ 4,149,838	$ 4,616,117
Other assets	36,846	52,342
Total assets	30,072,110	29,169,468
Liabilities
Long-term borrowings	6,440,345	5,227,512
Other liabilities	403,277	407,971
Total liabilities	27,912,190	27,288,671
Equity
Common stock, par value $0.20 per share, 1.125 billion shares authorized: 440.6 million and 438.2 million shares issued, respectively	88,121	87,647
Additional paid-in capital	1,193,753	1,148,689
Accumulated other comprehensive loss (net of tax benefit of $(21,209) and $(24,176), respectively)	(65,861)	(75,104)
Retained earnings	4,114,446	3,624,859
Total SLM Corporation stockholders’ equity before treasury stock	5,581,529	5,037,161
Less: Common stock held in treasury at cost: 230.2 million and 217.9 million shares, respectively	(3,421,609)	(3,156,364)
Total equity	2,159,920	1,880,797	1,726,970	$ 2,149,711
Total liabilities and equity	$ 30,072,110	$ 29,169,468
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)	440.6	438.2
Accumulated other comprehensive income, tax	$ 21,209	$ 24,176
Common stock held in treasury (in shares)	230.2	217.9
Series B Preferred Stock
Equity
Preferred stock liquidation preference (in dollars per share)	$ 100
Parent Company
Assets
Cash and cash equivalents	$ 391,481	$ 237,857	$ 196,820	$ 570,726
Total investments in subsidiaries (primarily Sallie Mae Bank)	2,773,211	2,628,838
Due from subsidiaries, net	43,556	63,679
Other assets	2,165	2,270
Total assets	3,210,413	2,932,644
Liabilities
Long-term borrowings	995,420	992,200
Income taxes payable, net	22,440	26,701
Other liabilities	32,633	32,946
Total liabilities	1,050,493	1,051,847
Equity
Common stock, par value $0.20 per share, 1.125 billion shares authorized: 440.6 million and 438.2 million shares issued, respectively	88,121	87,647
Additional paid-in capital	1,193,753	1,148,689
Accumulated other comprehensive loss (net of tax benefit of $(21,209) and $(24,176), respectively)	(65,861)	(75,104)
Retained earnings	4,114,446	3,624,859
Total SLM Corporation stockholders’ equity before treasury stock	5,581,529	5,037,161
Less: Common stock held in treasury at cost: 230.2 million and 217.9 million shares, respectively	(3,421,609)	(3,156,364)
Total equity	2,159,920	1,880,797
Total liabilities and equity	$ 3,210,413	$ 2,932,644
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)	440.6	438.2
Accumulated other comprehensive income, tax	$ 21,209	$ (24,176)
Common stock held in treasury (in shares)	230.2	217.9
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