Leases (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset	$ 74	$ 74
Finance Lease, Liability	85	85
Operating Lease, Expense	220	379
Operating Lease, Payments	192	337
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	174	201
Operating Lease, Right-of-Use Asset	2,740	2,740	$ 2,600	$ 0
Operating Lease, Liability, Noncurrent	2,258	2,258		0
Operating Lease, Liability	$ 2,838	$ 2,838	$ 2,700
Operating Lease, Weighted Average Remaining Lease Term	6 years 9 months 18 days	6 years 9 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent	3.60%	3.60%
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 344	$ 344
Lessee, Operating Lease, Liability, Payments, Due Year Two	629	629
Lessee, Operating Lease, Liability, Payments, Due Year Three	543	543
Lessee, Operating Lease, Liability, Payments, Due Year Four	412	412
Lessee, Operating Lease, Liability, Payments, Due Year Five	287	287
Lessee, Operating Lease, Liability, Payments, Due after Year Five	878	878
Lessee, Operating Lease, Liability, Payments, Due	3,093	3,093
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	255	255
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	580	580
Operating lease extensions [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due	$ 225	$ 225