Leases - Supplemental balance sheet information (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating leases:
Operating lease right-of-use assets (included in Other assets)	$ 203	$ 214
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other Assets, Noncurrent
Current operating lease liabilities (included in Other current liabilities)	$ 65
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current
Noncurrent operating lease liabilities (included in Other long-term liabilities)	$ 138
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent
Total operating lease liabilities	$ 203
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent us-gaap:OtherLiabilitiesNoncurrent
Finance leases:
Property, plant and equipment	$ 7,628		$ 7,024
Accumulated amortization	(4,355)		(3,939)
Net property, plant and equipment	3,273		$ 3,085
Current finance lease liabilities (included in Long-term debt due within one year)	$ 7
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Long-term Debt, Current Maturities
Noncurrent finance lease liabilities (included in Long-term debt)	$ 63
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Long-term Debt, Excluding Current Maturities
Total finance lease liabilities	$ 70
Finance Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtCurrent us-gaap:LongTermDebtNoncurrent
Weighted-average remaining lease term (in years):
Operating leases weighted-average remaining lease term (in years)	3 years 3 months 18 days
Finance leases weighted-average remaining lease term (in years)	7 years 4 months 24 days
Weighted-average discount rate:
Operating leases (as a percent)	7.78%
Finance leases (as a percent)	3.57%
Property, plant and equipment finance leases
Finance leases:
Property, plant and equipment	$ 107
Accumulated amortization	(33)
Net property, plant and equipment	$ 74