Leases (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset	$ 81
Finance Lease, Liability	86
Operating Lease, Expense	159
Operating Lease, Payments	145
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	27
Operating Lease, Right-of-Use Asset	2,533	$ 2,600	$ 0
Operating Lease, Liability, Noncurrent	2,020		0
Operating Lease, Liability	$ 2,602	$ 2,700
Operating Lease, Weighted Average Remaining Lease Term	6 years 11 months
Operating Lease, Weighted Average Discount Rate, Percent	3.60%
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 533
Lessee, Operating Lease, Liability, Payments, Due Year Two	540
Lessee, Operating Lease, Liability, Payments, Due Year Three	446
Lessee, Operating Lease, Liability, Payments, Due Year Four	327
Lessee, Operating Lease, Liability, Payments, Due Year Five	242
Lessee, Operating Lease, Liability, Payments, Due after Year Five	776
Lessee, Operating Lease, Liability, Payments, Due	2,864
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	262
Operating Leases, Future Minimum Payments Due			2,916
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	582
Operating lease extensions [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due	$ 228