Leases - Narrative Information (Details) $ in Millions		3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Obligations for leases that have not yet commenced	$ 42	$ 42
Lessee, Leases not yet commenced, term of lease	5 years
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating and finance leases term		1 year
Lesse, operating and finance leases, optional renewal terms		1 year
Lessor, Operating leases term	2 years	2 years
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating and finance leases term		62 years
Lesse, operating and finance leases, optional renewal terms		40 years
Lessor, Operating leases term	23 years	23 years