Lease Obligations (Additional Lease Information) (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Finance leases, weighted average remaining lease term (in years)	3 years
Finance leases, weighted average discount rate, percent	4.10%
Operating leases, weighted average remaining lease term (in years)	4 years 3 months 18 days
Operating leases, weighted average discount rate, percent	4.20%
Leases not yet commenced, future lease obligations	$ 18
Minimum [Member]
Lessee, Lease, Description [Line Items]
Leases not yet commenced, lease terms	1 year
Minimum [Member] | Facility Leases [Member]
Lessee, Lease, Description [Line Items]
Leases, renewal term	1 year
Maximum [Member]
Lessee, Lease, Description [Line Items]
Leases, remaining lease terms	10 years
Leases not yet commenced, lease terms	5 years
Maximum [Member] | Equipment Leases [Member]
Lessee, Lease, Description [Line Items]
Leases, renewal term	1 year
Maximum [Member] | Facility Leases [Member]
Lessee, Lease, Description [Line Items]
Leases, renewal term	5 years