Retirement Benefits - Narrative - Plan Descriptions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 1,005.0	$ 957.0
Retirement benefits, net	$ 38.0
First 3% of Compensation Contributed
Defined Benefit Plan Disclosure [Line Items]
Percent of company matching compensation contributed	100.00%
Percent of participant's compensation contributed	3.00%
Cost of 401(k) plan	$ 22.8	21.8	$ 21.4
Defined Contribution 401(k) Plan, Next 3% Contributed
Defined Benefit Plan Disclosure [Line Items]
Percent of company matching compensation contributed	50.00%
Percent of participant's compensation contributed	3.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total assets	$ 1,005.0	957.0	932.5
Projected benefit obligations, total	1,279.3	1,381.5	$ 1,349.8
Unfunded pension obligation	274.3	424.5
Employer contributions	18.8	$ 15.6
Pension Benefits | Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Expected cash contributions	15.0
Employer contributions	17.3
Amount expected to be recoverable	$ 20.0