Leases - Assets and Liabilities Lessee (Details) $ in Millions	Sep. 30, 2020 USD ($)
ROU assets:
Operating lease ROU assets	$ 415
Finance lease ROU assets	52
Total ROU assets	$ 467
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Lease liabilities:
Operating lease liabilities — current	$ 87
Operating lease liabilities — noncurrent	334
Finance lease liabilities — current	5
Finance lease liabilities — noncurrent	41
Total lease liabilities	$ 467
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations