Off-Balance Sheet Arrangements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Apr. 30, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Renewal term			1 year
HSA assets amount serving as custodian	$ 3,800.0		$ 3,800.0			$ 3,450.0
HSA assets deposited and managed by third party depository partners	1,100.0		1,100.0			1,400.0
HSA deposits	2,770.0		2,770.0			$ 2,070.0
Revolving Credit Facility | Secured Debt
Accounts, Notes, Loans and Financing Receivable [Line Items]
Borrowing capacity					$ 35.0
WEX Europe Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Losses on factoring	2.6	$ 0.0	4.5	$ 0.0
Proceeds from sale of factoring receivables	142.9	159.6	283.4	304.6
WEX Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of factoring receivables	3,300.0	$ 1,600.0	5,200.0	$ 2,400.0
WEX Health
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from sale of factoring receivables	$ 82.2		$ 82.2