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Retirement Plans and Other Postretirement Benefits - Narrative (Details) | 6 Months Ended
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Jun. 30, 2019 USD ($)
Pension Benefits |
Contributions |
Voluntary employer contributions to pension plan | $ 120,000,000
Minimum employer contributions for the next three years | 0
Maximum employer contributions for the next two years (up to) | 350,000,000
Other Benefits |
Contributions |
Estimated future employer contributions in next three years | $ 0

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