Debt - Debt Outstanding (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Sep. 22, 2020	Jul. 05, 2019	Jun. 07, 2019
Debt Instrument [Line Items]
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	$ 1,121.9	$ 1,172.8
Secured Debt | Term Loan due July 5, 2023
Debt Instrument [Line Items]
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	0.0	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: 2021 - $1,152.1; 2020 - $1,247.8)	$ 276.7	278.3
Senior Notes | Senior Notes Payable, 4.35% due 2025 (Fair Value: 2021 – $481.4; 2020 – $499.5)
Debt Instrument [Line Items]
Stated interest rate, percentage	4.35%
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	$ 449.0	448.8
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: 2021 - $1,152.1; 2020 - $1,247.8)	$ 396.2	$ 395.8
Subordinated Debt | Subordinated Debentures due 2054 (Fair Value: 2018 – $151.1)
Debt Instrument [Line Items]
Stated interest rate, percentage					7.375%