Fair Value - Financial Instruments (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Fair Value of Financial Instruments [Line Items]
Long-Term Debt, Including Long-Term Debt Due Within One Year - Carrying Amount	[1]	$ 1,806.4	$ 1,622.6
Level 2 [Member]
Fair Value of Financial Instruments [Line Items]
Long-Term Debt, Including Long-Term Debt Due Within One Year - Fair Value	[1]	$ 2,122.0	$ 1,791.8

[1] Excludes unamortized debt issuance costs.