Employee Benefits - Accumulated Benefit Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 3,010.5	$ 3,194.3
Information for pension or OPEB plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	372.4	1,555.5
Fair value of plan assets	186.3	1,298.3
Information for pension plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	383.0	2,034.1
Fair value of plan assets	186.3	1,729.8
OPEB Benefits
Information for pension or OPEB plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	25.1	25.7
Fair value of plan assets	$ 2.8	$ 3.0