Leases - Components of Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
ROU assets			$ 200
Lease liabilities	$ 71	$ 71	$ 200
Finance lease cost
Finance lease cost	2	7
Operating lease cost	434	820
Short-term lease cost	7	16
Variable lease cost	128	256
Sublease income	(6)	(8)
Total lease cost	$ 565	$ 1,090
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	$ 63	$ 63
Short-term debt
Lessee, Lease, Description [Line Items]
Lease liabilities	7	7
Long-term debt
Lessee, Lease, Description [Line Items]
Lease liabilities	$ 65	$ 65