Pension And Other Postretirement Benefits Benefit Obligation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Vesting percentage			100.00%
Required term of service to be eligible for plan match			1 year 1000 hours
Award vesting period			3 years
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate, Actuarial Present Value	5.00%		5.00%
Estimated nonqualified benefits in next fiscal year			$ 1.6
Non-cash pension settlement charge			27.7
Assets held in postretirement benefits plan	$ 722.0		722.0	$ 658.4
Estimated future employer contributions	$ 40.0		40.0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	2.72%	3.38%		4.31%	3.67%
Employer contributions			41.8	$ 11.7
Assets held in postretirement benefits plan	$ 722.0		722.0	658.4	$ 588.3
Accumulated benefit obligation	844.0		$ 844.0	$ 746.8
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate			3.19%	4.16%	3.44%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year, Net Periodic Benefit Cost			5.00%	5.00%	5.50%
Employer contributions			$ 4.7	$ 4.4
Assets held in postretirement benefits plan