Subsequent Events (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 20, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Subsequent Event [Line Items]
Remaining authority under the share repurchase program		$ 51,000,000		$ 51,000,000
Declared dividends per common share attributable to SLM Corporation (in dollars per share)		$ 0.03	$ 0	$ 0.09	$ 0.09
Subsequent Event
Subsequent Event [Line Items]
Declared dividends per common share attributable to SLM Corporation (in dollars per share)	$ 0.11
2021 Share Repurchase Program | Common Stock
Subsequent Event [Line Items]
Remaining authority under the share repurchase program		$ 51,000,000		$ 51,000,000
2021 Share Repurchase Program | Common Stock | Subsequent Event
Subsequent Event [Line Items]
Increase in amount of common stock that may be repurchased	$ 250,000,000