Fair Value - Fair Value of Financial Instruments and Assets Measured on a Nonrecurring Basis (Details) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020
Fair Value of Financial Instruments [Line Items]
Short-Term and Long-Term Debt - Carrying Amount	[1]	$ 2,036.1	$ 1,806.4
Level 2 [Member]
Fair Value of Financial Instruments [Line Items]
Short-Term and Long-Term Debt - Fair Value	[1]	$ 2,262.2	$ 2,122.0

[1] Excludes unamortized debt issuance costs.