Pension and Other Postretirement Plans - Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2018 USD ($)
Other Postretirement— subsidy receipts
2019	$ 5
2020	6
2021	6
2022	6
2023	7
Years 2024-2028	38
Pension Benefits
Pension and Other Postretirement
2019	329
2020	327
2021	353
2022	367
2023	379
Years 2024-2028	2,022
Other Postretirement Benefits
Pension and Other Postretirement
2019	100
2020	104
2021	108
2022	111
2023	113
Years 2024-2028	$ 575

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