Derivative Financial Instruments (Carrying Value of Hedged Items and Associated Cumulative Hedging Adjustment Relating for Fair Value Hedges) (Details) - Fair Value Hedges - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Carrying Value
Derivative Instruments, Gain (Loss) [Line Items]
Long-term Debt	$ 1,752.1	$ 1,747.0
Carrying Value | Derivatives not designated as hedging instruments (Non-qualifying Hedges)
Derivative Instruments, Gain (Loss) [Line Items]
Long-term Debt	1,246.4	499.4
Fair Value | Derivatives designated as hedging instruments (Qualifying Hedges)
Derivative Instruments, Gain (Loss) [Line Items]
Long-term Debt	6.9	2.1
Fair Value | Derivatives not designated as hedging instruments (Non-qualifying Hedges)
Derivative Instruments, Gain (Loss) [Line Items]
Long-term Debt	$ 2.6	$ 1.5