Leases Lease Term, Discount Rate, and Other Lease Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 239	$ 259
Operating Lease, Weighted Average Remaining Lease Term	5 years 113 days
Finance Lease, Weighted Average Remaining Lease Term	2 years 210 days
Operating Lease, Weighted Average Discount Rate, Percent	3.37%
Finance Lease, Weighted Average Discount Rate, Percent	3.25%
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee Operating and Finance Leases, Remaining Lease Term	1 year
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee Operating and Finance Leases, Remaining Lease Term	50 years
Residual Value Guarantee [Member]
Lessee, Lease, Description [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 46