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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 |

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