Leases Leases - Maturity of Lease Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Leases [Abstract]
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 51
Lessee, Operating Lease, Liability, Payments, Due Year Two	66
Lessee, Operating Lease, Liability, Payments, Due Year Three	66
Lessee, Operating Lease, Liability, Payments, Due Year Four	60
Lessee, Operating Lease, Liability, Payments, Due Year Five	57
Lessee, Operating Lease, Liability, Payments, Due after Year Five	917
Lessee, Operating Lease, Liability, Payments, Due	1,217
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(702)
Operating Lease, Liability	$ 515