Leases - Supplemental Balance Sheet Information Related to Leases (Details) $ in Millions	Dec. 31, 2019 USD ($)
Operating leases:
Operating lease assets	$ 2,245
Short-term operating lease liabilities	468
Operating lease liabilities	1,776
Total operating lease liabilities	2,244
Finance leases:
Property and equipment, gross	483
Accumulated depreciation	(125)
Property and equipment, net	358
Short-term borrowings and current maturities of long-term debt	58
Long-term debt	288
Total finance lease liabilities	$ 346
Weighted-average remaining lease term
Operating leases	7 years
Finance leases	7 years
Weighted-average discount rate
Operating leases	5.16%
Finance leases	2.69%