Postretirement Benefits Fair Values of Trust's Pension Assets (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
Dec. 31, 2018 |
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| Defined Benefit Plan Disclosure [Line Items] | |||
| Defined Contribution Plan Expense | $ 49.4 | $ 44.1 | $ 45.3 |
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
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| X | ||||||||||
- Definition Amount of cost for defined contribution plan. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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