Defined Contribution Plans (Details) - Sallie Mae 401(k) Savings Plan - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution percentage	100.00%
Type 1 of defined benefit contribution (up to)	5.00%
Employer contribution amount	$ 5.4	$ 5.0	$ 4.4

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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