Debt - Debt Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 22, 2020	Dec. 31, 2019	Jul. 05, 2019
Debt Instrument [Line Items]
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2020 - $1,247.8; 2019 - $820.2)	$ 1,172.8		$ 778.4
Secured Debt | Term Loan due July 5, 2023
Debt Instrument [Line Items]
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2020 - $1,247.8; 2019 - $820.2)	49.9		49.9	$ 49.9
Senior Notes | 5.000% Senior Notes due September 19, 2022
Debt Instrument [Line Items]
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2020 - $1,247.8; 2019 - $820.2)	$ 278.3		$ 279.9
Senior Notes | Senior Notes Payable, 4.35% due 2025 (Fair Value: 2020 – $499.5; 2019 – $478.6)
Debt Instrument [Line Items]
Stated interest rate, percentage	4.35%		4.35%
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2020 - $1,247.8; 2019 - $820.2)	$ 448.8		$ 448.6
Senior Notes | Senior Notes, 2.400 Percent Due September 30, 2030
Debt Instrument [Line Items]
Stated interest rate, percentage		2.40%
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2020 - $1,247.8; 2019 - $820.2)	$ 395.8		$ 0.0