Leases - Components of Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
ROU assets			$ 200
Lease liabilities	$ 155	$ 155	$ 200
Components of lease cost
Finance lease cost	7	14
Operating lease cost	423	1,243
Short-term lease cost	11	26
Variable lease cost	90	345
Sublease income	(7)	(16)
Total lease cost	$ 523	$ 1,613
Real estate
Lessee, Lease, Description [Line Items]
Average term (in years)	5 years	5 years
Equipment leases | Minimum
Lessee, Lease, Description [Line Items]
Average term (in years)	2 years	2 years
Equipment leases | Maximum
Lessee, Lease, Description [Line Items]
Average term (in years)	5 years	5 years
Property, plant and equipment
Lessee, Lease, Description [Line Items]
ROU assets	$ 140	$ 140
Short-term debt
Lessee, Lease, Description [Line Items]
Lease liabilities	34	34
Long-term debt
Lessee, Lease, Description [Line Items]
Lease liabilities	$ 121	$ 121