Leases - Classification of Operating and Finance Leases (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Leases
Operating lease right-of-use assets	$ 970	$ 975	$ 0
Short-term operating lease liabilities	115	112	0
Long-term operating lease liabilities	931	$ 949	0
Total operating lease liabilities	1,046
Finance Leases
Property, plant and equipment	12,522		12,074
Less: Accumulated depreciation and amortization	9,169		8,728
Property, plant and equipment, net	3,353		3,346
Current portion of long-term debt	21		21
Long-term debt, net	2,405		$ 2,418
Total finance lease liabilities	7
Operating leases
Operating Leases
Operating lease right-of-use assets	970
Short-term operating lease liabilities	115
Long-term operating lease liabilities	931
Total operating lease liabilities	1,046
Finance leases
Finance Leases
Property, plant and equipment	18
Less: Accumulated depreciation and amortization	5
Property, plant and equipment, net	13
Current portion of long-term debt	1
Long-term debt, net	6
Total finance lease liabilities	$ 7