Leases (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Finance Leases	$ 92
Finance Lease, lease not yet commenced, amount	$ 26
Finance Lease, lease not yet commenced, term of contract	5 years
Assets [Member]
Assets recorded under finance leases	$ 198
Accumulated Depreciation [Member]
Assets recorded under finance leases	109
Current Portion Of Long-Term Debt [Member]
Finance Leases	32
Long-term Debt [Member]
Finance Leases	$ 60
Variety Of Facilities [Member]
Option To Extend Lease Term	15 years
Lease, Option to Terminate	1 year
Maximum [Member] | Variety Of Facilities [Member]
Remaining Lease Term	23 years
Maximum [Member] | Vehicle Leases [Member]
Remaining Lease Term	8 years
Minimum [Member] | Variety Of Facilities [Member]
Remaining Lease Term	1 year
Minimum [Member] | Vehicle Leases [Member]
Remaining Lease Term	1 year