Pension and Other Postemployment Benefits (Details 8) $ in Millions	Dec. 31, 2017 USD ($)
Pension
Estimated Future Benefit Payments
2018	$ 518
2019	531
2020	552
2021	567
2022	581
2023-2027	3,056
OPEB
Estimated Future Benefit Payments
2018	55
2019	54
2020	53
2021	53
2022	52
2023-2027	241
Subsidy Receipts
2018	(1)
2019	(1)
2020	(1)
2021	(1)
2022	(1)
Years 2023-2027	$ (3)

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