Debt - Long Term Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Mar. 10, 2022	Feb. 15, 2022	Sep. 22, 2020
Debt Instrument [Line Items]
Long-Term Debt	$ 1,389.8		$ 1,389.2
Derivative, Gain (Loss) on Derivative, Net	0.5
Gain (Loss) on Derivative Instruments, Net, Pretax	0.1	$ 0.1
Senior Notes, 2.400 Percent Due September 30, 2030
Debt Instrument [Line Items]
Long-Term Debt						$ 395.8
Senior Notes, 3.800 Percent Due February 23, 2033
Debt Instrument [Line Items]
Long-Term Debt					$ 395.1
5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
Debt Instrument [Line Items]
Long-Term Debt				$ 144.7
Senior Notes | Senior Notes, 4.35 Percent Due February 15, 2025
Debt Instrument [Line Items]
Long-Term Debt	$ 0.0		449.6
Stated interest rate	4.35%
Long-term Debt, Current, at Amortized Cost (Fair Value: 2024 - $443.4; 2023 - $—)	$ 449.7		0.0
Senior Notes | Senior Notes, 2.400 Percent Due September 30, 2030
Debt Instrument [Line Items]
Long-Term Debt	397.1		397.0
Stated interest rate						2.40%
Senior Notes | Senior Notes, 3.800 Percent Due February 23, 2033
Debt Instrument [Line Items]
Long-Term Debt	396.1		396.0
Stated interest rate					3.80%
Senior Notes | 5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
Debt Instrument [Line Items]
Long-Term Debt	$ 146.9		$ 146.6
Junior Subordinated Debt [Member] | 5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
Debt Instrument [Line Items]
Stated interest rate				5.875%