Pension and Other Postretirement Benefit Plans - Reconciliation of Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet (Details) - Postretirement Health and Life [Member] - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net Loss	[1]	$ (23.0)	$ (16.0)
Prior Service Credit		28.3	36.3
Accumulated Net Periodic Benefit Cost in Excess of Contributions		13.1	3.6
Total Net Postretirement Health and Life Amounts Recognized in Consolidated Balance Sheet		$ 18.4	$ 23.9

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