Leases - Summary of Supplemental Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Lease Assets And Liabilities [Abstract]
Operating lease right-of-use assets	$ 1,985
Finance lease right-of-use assets	$ 18
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentMember
Total leased assets	$ 2,003
Operating leases liabilities	382
Finance lease liabilities, Current	$ 2
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
Non-current operating lease liabilities	$ 1,803
Non-current finance lease obligations	26	$ 25
Total lease liabilities	$ 2,213