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v3.20.4

Other Retirement Plans (Schedule of Covered Employees and Contributions, Multiemployer Plans) (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2020 USD ($) numberOfEmployees | Dec. 31, 2019 USD ($) numberOfEmployees | Dec. 31, 2018 USD ($) numberOfEmployees
Covered Employees and Contributions, Multiemployer Plans [Line Items] |  |  |
Multiemployer pension plans, contributions (in dollars) | $ 37.5 | $ 72.6 | $ 99.7
Low [Member] |  |  |
Covered Employees and Contributions, Multiemployer Plans [Line Items] |  |  |
Multiemployer plans, covered employees (in numberof employees) | numberOfEmployees | 1,119 | 1,119 | 1,626
High [Member] |  |  |
Covered Employees and Contributions, Multiemployer Plans [Line Items] |  |  |
Multiemployer plans, covered employees (in numberof employees) | numberOfEmployees | 2,412 | 5,349 | 6,336
Pension Plans [Member] |  |  |
Covered Employees and Contributions, Multiemployer Plans [Line Items] |  |  |
Multiemployer pension plans, contributions (in dollars) | $ 30.0 | $ 66.9 | $ 92.4
Other Multiemployer Plans [Member] |  |  |
Covered Employees and Contributions, Multiemployer Plans [Line Items] |  |  |
Multiemployer pension plans, contributions (in dollars) | $ 7.5 | $ 5.7 | $ 7.3

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- Definition Amount of cost for employer contribution to multiemployer plan. Multiemployer plan includes, but is not limited to, pension plan determined to be individually significant and insignificant and other postretirement benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=35742348&loc=SL14450788-114948 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=29639808&loc=d3e29008-114946 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450691-114947 + Details
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- Definition Number of entity's employees covered by multiemployer plan. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450673-114947 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65877416&loc=SL14450702-114947 + Details
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