Summary of Significant Accounting Policies - Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities
Accrued employee compensation liabilities	$ 106.7
Accrued customer settlement liabilities	41.1	$ 21.4
State and federal income tax liabilities	56.6
Accounts payable rebates	$ 101.7	$ 51.0