Regulatory Capital - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Allowance for credit losses on loans and leases		$ 1,165,335	$ 1,361,723	$ 441,912	$ 341,121
Allowance for credit losses on unfunded commitments		72,713	110,044	2,481	$ 2,165
Accounting Standards Update 2016-13
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Period of deferment	2 years
Amount deferred	25.00%
Allowance for credit losses on loans and leases	$ 1,100,000
Allowance for credit losses on unfunded commitments	116,000
Deferred tax asset	306,000
Reduction to retained earnings	$ 953,000
Sallie Mae Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends		$ 1,400,000	$ 579,000	$ 254,000