Leases (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset	$ 54	$ 54
Finance Lease, Liability	68	68
Operating Lease, Expense	194	573
Operating Lease, Payments	223	560
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	38	238
Operating Lease, Right-of-Use Asset	2,556	2,556	$ 2,600	$ 0
Operating Lease, Liability, Noncurrent	2,105	2,105		0
Operating Lease, Liability	$ 2,651	$ 2,651	$ 2,700
Operating Lease, Weighted Average Remaining Lease Term	6 years 10 months 24 days	6 years 10 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	3.60%	3.60%
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 186	$ 186
Lessee, Operating Lease, Liability, Payments, Due Year Two	695	695
Lessee, Operating Lease, Liability, Payments, Due Year Three	600	600
Lessee, Operating Lease, Liability, Payments, Due Year Four	473	473
Lessee, Operating Lease, Liability, Payments, Due Year Five	320	320
Lessee, Operating Lease, Liability, Payments, Due after Year Five	1,005	1,005
Lessee, Operating Lease, Liability, Payments, Due	3,279	3,279
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	628	628
Operating Leases, Future Minimum Payments Due				2,900
Operating Leases, Future Minimum Payments Due, Next Twelve Months				683
Operating Leases, Future Minimum Payments, Due in Two Years				544
Operating Leases, Future Minimum Payments, Due in Three Years				407
Operating Leases, Future Minimum Payments, Due in Four Years				301
Operating Leases, Future Minimum Payments, Due in Five Years				235
Operating Leases, Future Minimum Payments, Due Thereafter				$ 746
Accrued Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Current	546	546
Operating lease extensions [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due	$ 302	$ 302