Leases (Details) - USD ($) $ in Millions |
Jun. 30, 2019 |
Dec. 31, 2018 |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Operating Lease, Right-of-Use Asset | [1],[2] | $ 184 | |||||||||||
| Operating Lease, Liability | [3],[4] | 210 | |||||||||||
| Capital Leased Assets, Gross | $ 715 | ||||||||||||
| Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment | 6,860 | 6,832 | |||||||||||
| Lesse Operating Lease, Lease Not yet Commenced | $ 1 | ||||||||||||
| Lessee, Finance Lease, Term of Contract | 30 years | ||||||||||||
| Finance Lease, Liability | [3],[5] | $ 78 | |||||||||||
| Assets Held under Capital Leases [Member] | |||||||||||||
| Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment | $ 353 | ||||||||||||
| Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | |||||||||||||
| Operating Lease, Right-of-Use Asset | [1],[2] | 1 | |||||||||||
| Operating Lease, Liability | [3],[4] | 1 | |||||||||||
| Finance Lease, Liability | [3],[4] | 18 | |||||||||||
| Finance Lease, Right-of-Use Asset | [1],[2] | $ 17 | |||||||||||
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