Leases - Maturities of lease liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Finance Leases
2021	$ 20
2022	18
2023	18
2024	16
2025	10
After 2025	41
Total	123
Less: Amounts representing interest	8
Present value of future minimum lease payments	115	$ 132
Less: Current obligations	22	21
Long-term obligations	93	111
Operating Leases
2021	273
2022	201
2023	141
2024	93
2025	60
After 2025	162
Total	930
Less: Amounts representing interest	65
Present value of future minimum lease payments	865	854
Current operating lease liabilities	256	247
Noncurrent operating lease liabilities	$ 609	$ 607
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent us-gaap:OperatingLeaseLiabilityNoncurrent