Leases Maturity of lease liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Finance Lease Liabilities, Payments, Due [Abstract]
Finance Lease, Liability, Payments, Remainder of Fiscal Year	$ 50
Finance Lease, Liability, Payments, Due Year Two	65
Finance Lease, Liability, Payments, Due Year Three	62
Finance Lease, Liability, Payments, Due Year Four	58
Finance Lease, Liability, Payments, Due Year Five	56
Finance Lease, Liability, Payments, Due after Year Five	786
Finance Lease, Liability, Payments, Due	1,077
Finance Lease, Liability, Undiscounted Excess Amount	(517)
Finance Lease, Liability	560
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	2,035
Lessee, Operating Lease, Liability, Payments, Due Year Two	2,612
Lessee, Operating Lease, Liability, Payments, Due Year Three	2,477
Lessee, Operating Lease, Liability, Payments, Due Year Four	2,316
Lessee, Operating Lease, Liability, Payments, Due Year Five	2,203
Lessee, Operating Lease, Liability, Payments, Due after Year Five	16,588
Lessee, Operating Lease, Liability, Payments, Due	28,231
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	(7,467)
Operating Lease, Liability	20,764
Lessee, Liability, Payments, Remainder of Fiscal Year	2,085
Lessee, Liability, Payments, Due Year Two	2,677
Lessee, Liability, Payments, Due Year Three	2,539
Lessee, Liability, Payments, Due Year Four	2,374
Lessee, Liability, Payments, Due Year Five	2,259
Lessee, Liability, Payments, Due After Year Five	17,374
Lessee, Liability, Payments, Due	29,308
Lessee, Liability, Undiscounted Excess Amount	(7,984)
Lease, Liability	21,324
Operating Leases, Future Minimum Payments Due, Future Minimum Sublease Rentals	182
Operating And Capital Leases, Amount Due In Excess Of Remaining Estimated Economic Life	$ 2,100