Employee Benefits - Amounts Recognized on the Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB assets	$ 870.9	$ 916.7
Pension and OPEB obligations	176.0	171.6
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB assets	475.2	470.6
Pension and OPEB obligations	161.8	158.5
Total net assets	313.4	312.1
OPEB Benefits
Defined Benefit Plan Disclosure [Line Items]
Pension and OPEB assets	395.7	446.1
Pension and OPEB obligations	14.2	13.1
Total net assets	$ 381.5	$ 433.0