Financial Instruments - Carrying Amount and Estimated Fair Value of Asset (Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount | Short-term and Long-term Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	$ 847.2	$ 1,469.1
Carrying Amount | New Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	2,433.9	2,431.7
Fair Value | Short-term and Long-term Debt
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	1,056.1	1,811.8
Fair Value | New Term Loan Facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value disclosure of debt instrument	$ 2,476.2	$ 2,456.3