Leases (Supplemental Balance Sheet Information) (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Operating Leases:
Operating lease right-of-use assets, net	[1]	$ 502
Other current liabilities		61
Operating lease liabilities	[2]	447
Total operating lease liabilities		508
Finance Leases:
Accumulated depreciation		(12,731)	$ (11,932)
Property and equipment, net		15,083	$ 14,895
Current portion of long-term debt		8
Long-term debt		264
Total finance lease liabilities		272
Leasehold Improvements [Member]
Finance Leases:
Property and equipment, at cost		288
Accumulated depreciation		(49)
Property and equipment, net		$ 239

[1] Included in other assets.

[2] Included in other liabilities.