Derivatives and Fair Value Measurements - Long-term debt (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net carrying amount	$ 1,328.2	$ 1,547.8
Carrying amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt at par value	1,373.8	1,591.3
Less: Unamortized debt issuance costs and original issue discount	(45.6)	(43.5)
Net carrying amount	1,328.2	1,547.8
Estimated fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated fair value	$ 1,236.3	$ 987.6