Leases Lessee (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating Lease, Residual Value of Leased Asset	$ 283		$ 283
Lease charges	72	$ 72	191	$ 192
Operating lease right-of-use assets	2,365		2,365		$ 0
Operating Lease, Liability, Current	420		420
Long-term operating lease liabilities	1,966		1,966		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	184		540
Variable Lease, Cost	93		219
Sublease Income	(2)		(6)
Lease, Cost	275		753
Operating lease right-of-use assets	2,365		2,365
Long-term operating lease liabilities	1,966		1,966
Operating Lease, Liability	$ 2,386		$ 2,386
Operating Lease, Weighted Average Remaining Lease Term	9 years 4 months 24 days		9 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	4.50%		4.50%
Operating Lease, Payments			$ 564
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			149
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	$ 517		517
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	424		424
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	357		357
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	298		298
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	215		215
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	1,159		1,159
Lessee, Operating Lease, Liability, Payments, Due	2,970		2,970
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(584)		(584)
Vehicle leases [Member]
Lessee, Lease, Description [Line Items]
Lease, Cost	81		225
Finance Lease, Right-of-Use Asset, Amortization	8		31
Finance Lease, Interest Expense	1		3
Operating lease right-of-use assets	205		205
Operating Lease, Liability, Current	136		136
Long-term operating lease liabilities	69		69
Operating Lease, Liability	$ 205		$ 205
Operating Lease, Weighted Average Remaining Lease Term	1 year 8 months 12 days		1 year 8 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	2.91%		2.91%
Finance Lease, Right-of-Use Asset, Gross	$ 337		$ 337
Finance Lease, Right-of-Use Asset, Accumulated Amortization	(55)		(55)
Finance Lease, Right-of-Use Asset	282		282
Finance Lease, Liability, Current	96		96
Finance Lease, Liability, Noncurrent	164		164
Finance Lease, Liability	$ 260		$ 260
Finance Lease, Weighted Average Remaining Lease Term	1 year 10 months 24 days		1 year 10 months 24 days
Finance Lease, Weighted Average Discount Rate, Percent	1.77%		1.77%
Operating Lease, Payments			$ 182
Finance Lease, Interest Payment on Liability			3
Finance Lease, Principal Payments			193
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			209
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability			247
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	$ 140		140
Finance Lease, Liability, Payments, Due in Next Rolling Twelve Months	96		96
Finance Lease, Liability, Payments, Due in Rolling Year Two	21		21
Finance Lease, Liability, Payments, Due in Rolling Year Three	138		138
Finance Lease, Liability, Payments, Due in Rolling Year Four	5		5
Finance Lease, Liability, Payments, Due in Rolling Year Five	0		0
Finance Lease, Liability, Payments, Due in Rolling after Year Five	0		0
Finance Lease, Liability, Payment, Due	260		260
Finance Lease, Liability, Undiscounted Excess Amount	0		0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	52		52
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	15		15
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	4		4
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	0		0
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	0		0
Lessee, Operating Lease, Liability, Payments, Due	211		211
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	$ (6)		$ (6)