v3.19.3.a.u2
Leases - Supplemental balance sheet information (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Operating leases:    
Operating lease right of use assets $ 858  
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List] Operating lease right of use assets  
Current operating lease liabilities $ 247  
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] Current operating lease liabilities  
Noncurrent operating lease liabilities $ 607  
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Noncurrent operating lease liabilities  
Present value of future minimum lease payments $ 854  
Operating Lease, Liability, Statement of Financial Position [Extensible List] us-gaap:OtherLiabilitiesCurrent us-gaap:OperatingLeaseLiabilityNoncurrent  
Finance leases:    
Property and equipment, at cost $ 26,124 $ 24,873
Accumulated amortization (16,791) (16,135)
Property, Plant and Equipment - net 9,333 8,738
Current obligations of finance leases $ 21  
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List] Current obligations of finance leases  
Finance leases, net of current obligations $ 111 $ 75
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Finance leases, net of current obligations  
Finance Lease, Liability, Statement of Financial Position [Extensible List] us-gaap:OtherLiabilitiesCurrent us-gaap:OtherLiabilitiesNoncurrent  
Present value of future minimum lease payments $ 132  
Weighted average remaining lease term (in years):    
Operating leases weighted average remaining lease term (in years) 5 years 8 months 12 days  
Finance leases weighted average remaining lease term (in years) 9 years  
Weighted average discount rate:    
Operating leases weighted average discount rate (as a percent) 3.20%  
Finance leases weighted average discount rate (as a percent) 3.80%  
Property and equipment finance leases    
Finance leases:    
Property and equipment, at cost $ 239  
Accumulated amortization (102)  
Property, Plant and Equipment - net $ 137