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Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Land	$ 35	$ 36
Buildings	296	297
Leasehold and land improvements	1,210	1,178
Cell site equipment	3,460	3,411
Switching equipment	1,018	988
Office furniture and equipment	285	389
Other operating assets and equipment	51	57
System development	1,149	1,060
Work in process	274	212
Total property, plant and equipment, gross	7,778	7,628
Accumulated depreciation and amortization	(5,576)	(5,308)
Property, plant and equipment, net	2,202	2,320
Depreciation and amortization expense	627	604	$ 607
Loss on asset disposals	$ 10	$ 17	$ 22
Buildings
Property, Plant and Equipment [Line Items]
Useful life	20 years
Leasehold and land improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful life	1 year
Leasehold and land improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful life	30 years
Cell site equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	7 years
Cell site equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	25 years
Switching equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Switching equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	8 years
Office furniture and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Office furniture and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years
Other operating assets and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful life	3 years
Other operating assets and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful life	5 years
System development | Minimum
Property, Plant and Equipment [Line Items]
Useful life	1 year
System development | Maximum
Property, Plant and Equipment [Line Items]
Useful life	7 years

X

- Definition

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.

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Amount before accumulated depreciation of equipment commonly used in offices and stores that have no permanent connection to the structure of a building or utilities. Examples include, but are not limited to, desks, chairs, tables, and bookcases.

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Amount before accumulated depreciation of additions or improvements to assets held under a lease arrangement.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Premises equipment which performs the function of establishing and releasing connections on a per call basis between two or more circuts, services or communications systems.

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