Leases Leases - Effect of Adopting New Lease Standard (Details) - USD ($) $ in Millions		Mar. 31, 2019	Jan. 01, 2019		Dec. 31, 2018
Property and equipment, net		$ 15,922	$ 15,949	[1]	$ 16,045	[1]
Deferred Costs and Other Assets		856	848	[2],[3]	383	[2],[3]
Accrued Liabilities and Other Liabilities		1,169	1,247	[2]	1,217	[2]
Finance Lease, Liability, Noncurrent		9,990	9,961	[1]	10,057	[1]
Deferred Credits and Other Liabilities		$ 1,480	1,284	[2],[3]	$ 849	[2],[3]
Adjustments for New Accounting Pronouncement [Member]
Property and equipment, net	[1]		(96)
Deferred Costs and Other Assets	[2],[3]		465
Accrued Liabilities and Other Liabilities	[2]		30
Finance Lease, Liability, Noncurrent	[1]		(96)
Deferred Credits and Other Liabilities	[2],[3]		$ 435

[1] Non-operating land assets previously considered as failed sale-leaseback financing obligations were determined to qualify for sale-leaseback accounting under ASC 842 and are now recognized as operating lease liabilities with corresponding ROU assets.

[2] (2) Operating leases previously considered as off-balance sheet obligations are now recognized as operating lease liabilities with corresponding ROU assets.

[3] (3) Accruals associated with future obligations for leases not in use have been applied against the carrying amount of the ROU assets.