Postretirement Health Care and Life Insurance Benefits Fair Value of Plan Assets in Non-Represented Trust by Asset (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	50.00%
Voluntary Employees Beneficiary Association, Contribution Amount	$ 17.0
Assets for Plan Benefits, Defined Benefit Plan	13.4	$ 0.0
Fair Value of Assets in Trust	34.2	15.0
Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Assets in Trust	20.5	15.0
Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Assets in Trust		0.0
Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Assets in Trust	0.0	0.0
Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan		15.0
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan		15.0
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan		0.0
Fair Value of Assets in Trust	13.7
Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan		$ 0.0
U.S. equity securities | Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	13.0
U.S. equity securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	13.0
U.S. equity securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
U.S. equity securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
International equity securities | Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	4.0
International equity securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	4.0
International equity securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
International equity securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
Corporate bonds | Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	9.2
Corporate bonds | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
Corporate bonds | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	9.2
Corporate bonds | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
U.S. government securities | Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	7.1
U.S. government securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	2.6
U.S. government securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	4.5
U.S. government securities | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
Cash funds | Other Postretirement Benefits Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.9
Cash funds | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.9
Cash funds | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	0.0
Cash funds | Other Postretirement Benefits Plan | Fair Value, Inputs, Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Assets for Plan Benefits, Defined Benefit Plan	$ 0.0