Leases (Narrative) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Lease expense	$ 44	$ 124
Operating lease cost	37	108
Finance lease cost	7	16
Lease liabilities	30	85
Operating cash flows from operating leases	$ 26	$ 74
Operating leases weighted average remaining term	12 years 7 months 6 days	12 years 7 months 6 days
Finance leases weighted average remaining term	11 years 1 month 6 days	11 years 1 month 6 days
Operating leases weighted average discount rate	4.10%	4.10%
Finance leases weighted average discount rate	5.50%	5.50%
Lease not yet commenced	$ 284	$ 284
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lease term	10 years	10 years
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lease term	20 years	20 years