Leases Lease, Classification (Details) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset	[1]	$ 1,164	$ 0
Finance Lease, Right-of-Use Asset		14
Operating and Finance Lease, Right-of-Use Asset		1,178
Operating Lease, Liability		1,238
Finance Lease, Liability		16
Operating and Finance Lease Liabilities		$ 1,254
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		5 years
Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract		10 years

[1] See Note 10, “Leases,” for additional information.