Regulatory Capital - Additional Information (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends									$ 0	$ 120,000,000	$ 420,000,000
Preferred stock dividends	4,855,000	4,850,000	3,228,000	0	0	0	0	0	12,933,000	0	0
Sallie Mae Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends									$ 0	$ 120,000,000	$ 420,000,000