Lease Commitments Lease Commitments (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Lessee, Finance Lease, Lease Not yet Commenced	$ 400
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 80
Operating Lease, Weighted Average Remaining Lease Term	6 years 10 months
Finance Lease, Weighted Average Remaining Lease Term	12 years 8 months
Operating Lease, Weighted Average Discount Rate, Percent	3.50%
Finance Lease, Weighted Average Discount Rate, Percent	3.50%
Operating Leases, Future Minimum Payments Due		$ 1,511
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	$ 16
Operating Lease, Liability, Current	335	0
Operating Lease, Liability, Noncurrent	1,025	0
Operating Lease, Liability	1,360
Finance Lease, Right-of-Use Asset	8,654
Finance Lease, Liability	165
Operating Leases, Future Minimum Payments Receivable, Current		363
Operating Leases, Future Minimum Payments, Due in Two Years		271
Operating Leases, Future Minimum Payments, Due in Three Years		193
Operating Leases, Future Minimum Payments, Due in Four Years		141
Operating Leases, Future Minimum Payments, Due in Five Years		106
Operating Leases, Future Minimum Payments, Due Thereafter		$ 437
Lessee, Operating Lease, Liability, Payments, Due	376
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	282
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	199
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	146
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	113
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	428
Lessee, Operating Lease, Liability, Payments, Due	1,544
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	184
Finance Lease, Liability, Payments, Due in Next Rolling Twelve Months	95
Finance Lease, Liability, Payments, Due in Rolling Year Two	29
Finance Lease, Liability, Payments, Due in Rolling Year Three	20
Finance Lease, Liability, Payments, Due in Rolling Year Four	15
Finance Lease, Liability, Payments, Due in Rolling Year Five	10
Finance Lease, Liability, Payments, Due in Rolling after Year Five	7
Finance Lease, Liability, Payments, Due	176
Finance Lease, Liability, Undiscounted Excess Amount	11
Operating Lease, Payments	106
Finance Lease, Interest Payment on Liability	1
Finance Lease, Principal Payments	8
Operating Lease, Expense	110
Variable Lease, Cost	19
Sublease Income	(4)
Finance Lease, Right-of-Use Asset, Amortization	3
Finance Lease, Interest Expense	1
Lease, Cost	129
Other Noncurrent Assets [Member]
Lessee, Lease, Description [Line Items]
Other Assets, Noncurrent	1,321
Other Current Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Current	335
Other Noncurrent Liabilities [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Liability, Noncurrent	1,025
Property, Plant and Equipment [Member]
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset	195
Operating Segments [Member] | Automotive | Debt [Member]
Lessee, Lease, Description [Line Items]
Finance Lease, Liability, Current	90
Finance Lease, Liability, Noncurrent	$ 75