Leases Lessee (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating Lease, Residual Value of Leased Asset	$ 292
Operating lease right-of-use assets	2,506	$ 0
Operating Lease, Liability, Current	474
Long-term operating lease liabilities	2,046	0
Operating Leases, Future Minimum Payments Due, Next Twelve Months		835
Operating Leases, Future Minimum Payments, Due in Two Years		476
Operating Leases, Future Minimum Payments, Due in Three Years		345
Operating Leases, Future Minimum Payments, Due in Four Years		253
Operating Leases, Future Minimum Payments, Due in Five Years		162
Operating Leases, Future Minimum Payments, Due Thereafter		590
Operating Leases, Future Minimum Payments Due		$ 2,661
Property leases [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	177
Variable Lease, Cost	51
Lease, Cost	228
Operating lease right-of-use assets	2,506
Long-term operating lease liabilities	2,046
Operating Lease, Liability	$ 2,520
Operating Lease, Weighted Average Remaining Lease Term	9 years 6 months
Operating Lease, Weighted Average Discount Rate, Percent	4.58%
Operating Lease, Payments	$ 189
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	(113)
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	615
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	404
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	359
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	304
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	252
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	1,220
Lessee, Operating Lease, Liability, Payments, Due	3,154
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(634)
Vehicle leases [Member]
Lessee, Lease, Description [Line Items]
Lease, Cost	69
Finance Lease, Right-of-Use Asset, Amortization	11
Finance Lease, Interest Expense	1
Operating lease right-of-use assets	147
Operating Lease, Liability, Current	82
Long-term operating lease liabilities	65
Operating Lease, Liability	$ 147
Operating Lease, Weighted Average Remaining Lease Term	2 years 10 months
Operating Lease, Weighted Average Discount Rate, Percent	3.09%
Finance Lease, Right-of-Use Asset, Gross	$ 282
Finance Lease, Right-of-Use Asset, Accumulated Amortization	(50)
Finance Lease, Right-of-Use Asset	232
Finance Lease, Liability, Current	82
Finance Lease, Liability, Noncurrent	117
Finance Lease, Liability	$ 199
Finance Lease, Weighted Average Remaining Lease Term	1 year 10 months
Finance Lease, Weighted Average Discount Rate, Percent	1.40%
Operating Lease, Payments	$ 27
Finance Lease, Interest Payment on Liability	1
Finance Lease, Principal Payments	38
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	(8)
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	35
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	87
Finance Lease, Liability, Payments, Due in Next Rolling Twelve Months	82
Finance Lease, Liability, Payments, Due in Rolling Year Two	12
Finance Lease, Liability, Payments, Due in Rolling Year Three	100
Finance Lease, Liability, Payments, Due in Rolling Year Four	5
Finance Lease, Liability, Payments, Due in Rolling Year Five	0
Finance Lease, Liability, Payments, Due in Rolling after Year Five	0
Finance Lease, Liability, Payments, Due	199
Finance Lease, Liability, Undiscounted Excess Amount	0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	43
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	16
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	6
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	0
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	0
Lessee, Operating Lease, Liability, Payments, Due	152
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(5)
Property, Plant and Equipment, Other Types [Member]
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset, Gross	25
Finance Lease, Right-of-Use Asset, Accumulated Amortization	(2)
Finance Lease, Right-of-Use Asset	23
Finance Lease, Liability, Current	8
Finance Lease, Liability, Noncurrent	15
Finance Lease, Liability	$ 23
Finance Lease, Weighted Average Remaining Lease Term	4 years
Finance Lease, Weighted Average Discount Rate, Percent	5.86%
Finance Lease, Liability, Payments, Due in Next Rolling Twelve Months	$ 9
Finance Lease, Liability, Payments, Due in Rolling Year Two	6
Finance Lease, Liability, Payments, Due in Rolling Year Three	3
Finance Lease, Liability, Payments, Due in Rolling Year Four	3
Finance Lease, Liability, Payments, Due in Rolling Year Five	2
Finance Lease, Liability, Payments, Due in Rolling after Year Five	3
Finance Lease, Liability, Payments, Due	26
Finance Lease, Liability, Undiscounted Excess Amount	$ (3)