Stockholders' Equity - Additional Information (Details) - USD ($)							1 Months Ended		3 Months Ended			6 Months Ended
	Mar. 16, 2021	Mar. 10, 2021	Jan. 28, 2021	Jan. 26, 2021	Mar. 11, 2020	Mar. 10, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Feb. 02, 2021	Jan. 27, 2021	Dec. 31, 2020	Jan. 22, 2020
Class of Stock [Line Items]
Common stock dividend (in usd per share)							$ 0.03	$ 0.03
Declared dividends per common share attributable to SLM Corporation (in dollars per share)								$ 0.03	$ 0.03		$ 0.06	$ 0.06	$ 0.09
Aggregate purchase price (not to exceed)																	$ 600,000,000
Common stock repurchased, amount						$ 525,000,000
Common stock repurchased (in shares)		45,000,000	13,000,000		45,000,000				22,806,841		0	71,509,671	47,736,847
Average purchase price per share (in usd per share)									$ 18.80		$ 7.77	$ 14.32	$ 10.98
Remaining authority under the share repurchase program							$ 295,000,000		$ 295,000,000			$ 295,000,000
Common stock, par value (in dollars per share)							$ 0.20		$ 0.20			$ 0.20				$ 0.20
Common stock repurchased												$ 1,027,298,000	$ 558,167,000
Common stock repurchased and cancelled (in shares)	28,500,000
Common Stock
Class of Stock [Line Items]
Common stock repurchased (in shares)									22,806,841			43,007,211	47,736,847
Tender Offer | Additional Paid-In Capital
Class of Stock [Line Items]
Common stock purchase cancelled, common stock balance													$ 466,000,000
Tender Offer | Common Stock
Class of Stock [Line Items]
Common stock purchase cancelled, common stock balance													$ 6,000,000
Common Stock
Class of Stock [Line Items]
Common stock closing price (in usd per share)							$ 20.94		$ 20.94			$ 20.94
Common Stock | 2020 Share Repurchase Program
Class of Stock [Line Items]
Common stock repurchased, amount										$ 75,000,000
Common stock repurchased (in shares)				58,000,000						4,000,000
Treasury stock, additional shares received				13,000,000
Average purchase price per share (in usd per share)				$ 9.01
Common Stock | 2021 Share Repurchase Program
Class of Stock [Line Items]
Aggregate purchase price (not to exceed)															$ 1,250,000,000
Common stock repurchased, amount									$ 439,000,000			$ 957,000,000
Common stock repurchased (in shares)									22,800,000			53,800,000
Remaining authority under the share repurchase program							$ 295,000,000		$ 295,000,000			$ 295,000,000
Common Stock | Tender Offer
Class of Stock [Line Items]
Aggregate purchase price (not to exceed)														$ 1,000,000,000
Common stock repurchased (in shares)		28,500,000
Average purchase price per share (in usd per share)		$ 16.50
Common stock, par value (in dollars per share)														$ 0.20
Common stock repurchased	$ 472,000,000
Common Stock | Rule 10b5-1 Trading Plan
Class of Stock [Line Items]
Common stock repurchased, amount									$ 439,000,000			$ 560,000,000
Common stock repurchased (in shares)									22,800,000			29,600,000