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Pension and Postretirement Benefit Costs (Details) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2019 USD ($) qualified_pension_plans | Sep. 30, 2018 USD ($) | Sep. 30, 2019 USD ($) qualified_pension_plans | Sep. 30, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Voluntary Employees Beneficiary Association, Contribution Amount | $ 17.0 |  | $ 17.0 |
Components of net periodic benefit cost |  |  |  |
Net periodic cost | 4.9 | $ 4.5 | 14.6 | $ 13.6
Other Defined Benefit Plan Information [Abstract] |  |  |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 20.0 |  | $ 20.0 |
Number of Qualified Pension Plans | qualified_pension_plans | 1 |  | 1 |
Defined benefit pension plans |  |  |  |
Components of net periodic benefit cost |  |  |  |
Service cost for benefits earned | $ 0.5 | 0.6 | $ 1.5 | 1.7
Interest cost on projected benefit obligation | 8.4 | 7.9 | 25.1 | 23.6
Expected return on plan assets | (7.9) | (10.7) | (23.5) | (32.1)
Net periodic cost | $ 1.0 | (2.2) | $ 3.1 | (6.8)
Other Defined Benefit Plan Information [Abstract] |  |  |  |
Funding threshold | 80.00% |  | 80.00% |
Postretirement benefit plans |  |  |  |
Components of net periodic benefit cost |  |  |  |
Service cost for benefits earned | $ 1.2 | 2.1 | $ 3.6 | 6.2
Interest cost on projected benefit obligation | 6.3 | 7.0 | 18.9 | 21.2
Expected return on plan assets | (0.2) | 0.0 | (0.4) | 0.0
Amortization of prior service cost and net actuarial loss | (2.2) | 0.0 | (6.6) | 0.0
Net periodic cost | $ 5.1 | $ 9.1 | $ 15.5 | $ 27.4

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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