Leases Leases (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) Rate
Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset	$ 257
Operating Lease, Liability, Current	55
Operating Lease, Liability, Noncurrent	$ 211
Lessee, Lease, Description [Line Items]
Document Period End Date	Mar. 31, 2019
Lessee, leases not yet commenced, amount	$ 63
Operating Lease, Payments	17
Operating Lease, Cost	$ 18
Operating Lease, Weighted Average Remaining Lease Term	5 years 3 months 10 days
Finance Lease, Weighted Average Discount Rate, Percent | Rate	3.61%
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 54
Lessee, Operating Lease, Liability, Payments, Due Year Two	60
Lessee, Operating Lease, Liability, Payments, Due Year Three	48
Lessee, Operating Lease, Liability, Payments, Due Year Four	39
Lessee, Operating Lease, Liability, Payments, Due Year Five	30
Lessee, Operating Lease, Liability, Payments, Due after Year Five	65
Lessee, Operating Lease, Liability, Payments, Due	297
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	31
Operating Lease, Liability	$ 266
Earliest year of commencement for leases not yet commenced	2019
Latest year of commencement for leases not yet commenced	2020
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	6 months
Lessee, Operating and Finance Leases, Term of Contract	1 year
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Lease Not yet Commenced, Term of Contract	15 years
Lessee, Operating and Finance Leases, Term of Contract	60 years
Lessee, Operating and Finance Leases, Option to Extend	10 years