Employee Benefits - Accumulated Benefit Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 2,279.6	$ 2,250.6
Information for pension or OPEB plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	300.7	185.7
Fair value of plan assets	147.3	32.8
Information for pension plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	306.7	191.3
Fair value of plan assets	147.3	32.8
OPEB Benefits
Information for pension or OPEB plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	21.0	20.6
Fair value of plan assets	$ 6.9	$ 7.4