Lease Commitments Lease Commitments (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Operating Lease Right-of-Use Assets and Liabilities
Operating lease liabilities	$ 327	$ 327	$ 0
Operating lease liabilities	1,013	1,013	0
Total operating lease liabilities	1,340	1,340
Finance Lease Right-of-Use Assets and Liabilities
Finance Lease, Right-Of-Use Asset, Accumulated Depreciation	(39)	(39)
Total finance lease liabilities	161	161
Minimum Non-Cancellable Lease Commitments
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
Operating Leases, Future Minimum Payments Due			$ 1,511
Operating Lease Liabilities, Payments, Due, Rolling Maturity [Abstract]
Within one year	367	367
After one year and within two years	275	275
After two years and within three years	196	196
After three years and within four years	146	146
After four years and within five years	115	115
After five years	421	421
Total	1,520	1,520
Less: Present value discount	180	180
Lessee, Finance Lease, Lease Not yet Commenced, Future Payments	$ 400	$ 400
Lessee, Finance Lease, Lease Not yet Commenced, Term of Contract	20 years	20 years
Finance Lease Liabilities, Payments, Rolling Maturity [Abstract]
Within one year	$ 94	$ 94
After one year and within two years	27	27
After two years and within three years	20	20
After three years and within four years	15	15
After four years and within five years	9	9
After five years	6	6
Total	171	171
Less: Present value discount	10	10
Supplemental Cash Flow Information [Abstract]
Operating cash flows from operating leases		215
Operating cash flows from finance leases		3
Financing cash flows from finance leases		17
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		142
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability		20
Components of Lease Expense
Operating lease expense	110	220
Variable lease expense	12	31
Sublease income	(4)	(8)
Amortization of right-of-use assets	4	7
Interest on lease liabilities	2	3
Total lease expense	$ 124	$ 253
Weighted Average Remaining Lease Term and Rate [Abstract]
Operating Lease, Weighted Average Remaining Lease Term	6 years 9 months 18 days	6 years 9 months 18 days
Finance Lease, Weighted Average Remaining Lease Term	3 years	3 years
Operating Lease, Weighted Average Discount Rate, Percent	3.50%	3.50%
Finance Lease, Weighted Average Discount Rate, Percent	3.50%	3.50%
Other Noncurrent Assets
Operating Lease Right-of-Use Assets and Liabilities
Other assets, non-current	$ 1,299	$ 1,299
Other Current Liabilities
Operating Lease Right-of-Use Assets and Liabilities
Operating lease liabilities	327	327
Other Noncurrent Liabilities
Operating Lease Right-of-Use Assets and Liabilities
Operating lease liabilities	1,013	1,013
Property, Plant and Equipment
Finance Lease Right-of-Use Assets and Liabilities
Property and equipment, gross	234	234
Property and equipment, net	195	195
Operating Segments | Automotive | Debt
Finance Lease Right-of-Use Assets and Liabilities
Automotive debt payable within one year	89	89
Automotive long-term debt	$ 72	$ 72
Minimum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	1 year	1 year
Maximum
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	40 years	40 years