Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,064.7	$ 512.4
Total service revenue
Disaggregation of Revenue [Line Items]
Revenue	849.1	343.6
Commissions
Disaggregation of Revenue [Line Items]
Revenue	227.4	130.6
Buyer fees
Disaggregation of Revenue [Line Items]
Revenue	502.7	140.7
Marketplace services revenue
Disaggregation of Revenue [Line Items]
Revenue	119.0	72.3
Inventory sales revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 215.6	$ 168.8