Leases Supplemental balance sheet information (Details) $ in Millions |
Mar. 31, 2019
USD ($)
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| Supplemental balance sheet information [Abstract] | ||||||
| Operating Lease, Right-of-Use Asset | $ 182 | [1] | ||||
| Finance Lease, Right-of-use Asset, Gross | 390 | [2] | ||||
| Finance Lease, Right-of-use Asset, Accumulated Amortization | (177) | [2] | ||||
| Finance Lease, Right-of-Use Asset | $ 213 | [2] | ||||
| Operating Lease, Weighted Average Remaining Lease Term | 15 years 7 months 28 days | |||||
| Finance Lease, Weighted Average Remaining Lease Term | 12 years 1 month 6 days | |||||
| Operating Lease, Weighted Average Discount Rate, Percent | 5.30% | |||||
| Finance Lease, Weighted Average Discount Rate, Percent | 7.50% | |||||
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