Leases (Details) - USD ($) $ in Millions |
Sep. 30, 2019 |
Dec. 31, 2018 |
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|---|---|---|---|---|---|---|---|---|---|
| Operating Lease, Right-of-Use Asset | [1] | $ 175 | |||||||
| Operating Lease, Liability | [2] | 208 | |||||||
| Capital Leased Assets, Gross | $ 715 | ||||||||
| Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment | 6,855 | 6,832 | |||||||
| Lesse Operating Lease, Lease Not yet Commenced | $ 5 | ||||||||
| Lessee, Finance Lease, Term of Contract | 30 years | ||||||||
| Finance Lease, Liability | [3] | $ 78 | |||||||
| Assets Held under Capital Leases [Member] | |||||||||
| Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment | $ 353 | ||||||||
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