Pension and Other Postretirement Benefit Plans - Obligation and Funded Status (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Plan Assets [Roll Forward]
Non-Current Liabilities		$ (225.8)	$ (172.8)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Loss	[1]	(23.0)	(16.0)
Change in Benefit Obligation [Roll Forward]
Obligation, Beginning of Year		149.8	176.0
Service Cost		3.3	3.9	$ 4.7
Interest Cost	[2]	5.0	7.3	7.1
Plan Amendments	[3]	0.0	(34.6)
Plan Curtailments		(0.3)	(2.1)
Actuarial (Gain) Loss	[4]	19.2	10.5
Benefits Paid		(12.6)	(14.7)
Participant Contributions		3.2	3.5
Obligation, End of Year		167.6	149.8	176.0
Change in Plan Assets [Roll Forward]
Fair Value, Beginning of Year		173.7	154.3
Actual Return on Plan Assets		20.9	29.5
Employer Contribution		0.8	1.1
Defined Benefit Plan Contributions by Plan Participants, Excluding Key Employees		3.2	3.5
Benefits Paid		(12.6)	(14.7)
Fair Value, End of Year		186.0	173.7	154.3
Funded Status, End of Year		18.4	23.9
Non-Current Assets		34.2	37.5
Current Liabilities		(0.6)	(0.7)
Non-Current Liabilities		(15.2)	(12.9)
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Loss		(299.0)	(243.4)
Accumulated Benefit Obligation		931.2	812.0
Change in Benefit Obligation [Roll Forward]
Obligation, Beginning of Year		854.0	747.0
Service Cost		10.7	9.3	11.0
Interest Cost	[5]	27.9	31.9	29.6
Actuarial (Gain) Loss	[6]	118.7	98.3
Benefits Paid		(54.4)	(53.4)
Participant Contributions		8.8	20.9
Obligation, End of Year		965.7	854.0	747.0
Change in Plan Assets [Roll Forward]
Fair Value, Beginning of Year		699.6	598.0
Actual Return on Plan Assets		93.0	122.1
Employer Contribution	[7]	21.2	32.9
Benefits Paid		(54.4)	(53.4)
Fair Value, End of Year		759.4	699.6	$ 598.0
Funded Status, End of Year		(206.3)	(154.4)
Current Liabilities		(2.2)	(1.6)
Non-Current Liabilities		$ (204.1)	$ (152.8)

[1] Excludes gains, losses and contributions associated with irrevocable grantor trusts.

[2] These components of net periodic postretirement health and life cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.

[3] Plan design changes under the other postretirement benefit plans resulted in a decrease to the benefit obligation of $34.6 million in 2019.

[4] Actuarial loss was primarily the result of decreases in discount rates in 2020 and 2019.

[5] These components of net periodic pension cost are included in the line item “Other” under Other Income (Expense) on the Consolidated Statement of Income.

[6] Actuarial loss was primarily the result of decreases in discount rates in 2020 and 2019.

[7] Includes Participant Contributions noted above.