Financial Instruments - Carrying Amount and Estimated Fair Value of Asset (Liability) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Carrying amount | Short-term and Long-term Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	$ 850.1	$ 847.2
Carrying amount | New Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	2,721.5	2,433.9
Fair value | Short-term and Long-term Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	1,015.2	1,056.1
Fair value | New Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	$ 2,812.4	$ 2,476.2