Leases Leases - Financing Obligation Service Requirements (Details) $ in Millions	Mar. 31, 2019 USD ($)
Finance Lease, Liability, Payments, Remainder of Fiscal Year	$ 590	[1]
Finance Lease, Liability, Payments, Due Year Two	800	[1]
Finance Lease, Liability, Payments, Due Year Three	814	[1]
Finance Lease, Liability, Payments, Due Year Four	827	[1]
Finance Lease, Liability, Payments, Due Year Five	847	[1]
Finance Lease, Liability, Payments, Due after Year Five	34,018	[1]
Finance Lease, Liability, Payments, Due	37,896	[1]
Principal [Member]
Finance Lease, Liability, Payments, Remainder of Fiscal Year	14
Finance Lease, Liability, Payments, Due Year Two	23
Finance Lease, Liability, Payments, Due Year Three	26
Finance Lease, Liability, Payments, Due Year Four	28
Finance Lease, Liability, Payments, Due Year Five	33
Finance Lease, Liability, Payments, Due after Year Five	8,400
Finance Lease, Liability, Payments, Due	8,524
Interest [Member]
Finance Lease, Liability, Payments, Remainder of Fiscal Year	576
Finance Lease, Liability, Payments, Due Year Two	777
Finance Lease, Liability, Payments, Due Year Three	788
Finance Lease, Liability, Payments, Due Year Four	799
Finance Lease, Liability, Payments, Due Year Five	814
Finance Lease, Liability, Payments, Due after Year Five	25,618
Finance Lease, Liability, Payments, Due	$ 29,372

[1] (1) Financing obligation principal and interest payments are estimated amounts based on the future minimum lease payments and certain estimates based on contingent rental payments. Actual payments may differ from the estimates.