Leases Lease, Operating and Finance Lease Maturity (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating and Finance Lease Maturity [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	$ 185
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	191
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	180
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	163
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	142
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	573
Lessee, Operating Lease, Liability, Payments, Due	1,434
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(196)
Operating Lease, Liability	1,238
Finance Lease, Liability, Payments, Due in Next Rolling Twelve Months	5
Finance Lease, Liability, Payments, Due in Rolling Year Two	3
Finance Lease, Liability, Payments, Due in Rolling Year Three	3
Finance Lease, Liability, Payments, Due in Rolling Year Four	4
Finance Lease, Liability, Payments, Due in Rolling Year Five	1
Finance Lease, Liability, Payments, Due in Rolling after Year Five	1
Finance Lease, Liability, Payments, Due	17
Finance Lease, Liability, Undiscounted Excess Amount	(1)
Finance Lease, Liability	16
Operating and Finance Lease, Liability, Payments Due in Next Rolling Twelve Months	190
Operating and Finance Lease, Liability, Payments Due in Rolling Year Two	194
Operating and Finance Lease, Liability, Payments Due in Rolling Year Three	183
Operating and Finance Lease, Liability, Payments Due in Rolling Year Four	167
Operating and Finance Lease, Liability, Payments Due in Rolling Year Five	143
Operating and Finance Lease, Liability, Payments Due in Rolling After Year Five	574
Operating and Finance Lease, Liability, Payments, Due	1,451
Operating and Finance Lease, Liability, Undiscounted Excess Amount	(197)
Operating and Finance Lease Liabilities	$ 1,254