Employee Benefits - Amounts Recognized on the Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB assets	$ 881.3	$ 600.9
Pension and OPEB obligations	219.0	327.0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB assets	389.0	182.9
Pension and OPEB obligations	196.7	304.3
Total net (liabilities) assets	192.3	(121.4)
OPEB Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB assets	492.3	418.0
Pension and OPEB obligations	22.3	22.7
Total net (liabilities) assets	$ 470.0	$ 395.3