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Pension and Other Postretirement Benefits - Company matching contribution to defined contribution 401(K) plans (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Retirement Benefits [Abstract] |  |  |
Age requirement for future accruals | 50 years |  |
Company matching contribution to defined contribution (401(k)) plans | $ 4.9 | $ 4.9 | $ 4.4

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- Definition Defined Contribution Plan, Age Requirement for Future Accruals + References No definition available. + Details
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- References No definition available. + Details
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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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