Segment Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting, Revenue Reconciling Item [Line Items]
Goodwill	$ 7,741		$ 7,741		$ 7,729
Assets	25,373		25,373		24,888
Payments to Acquire Productive Assets	322	$ 364	1,018	$ 1,028
Adjusted EBITDA by Segment	721	716	2,148	2,141
Revenue	2,059	2,033	6,168	6,140
Income Tax Expense	(76)	(74)	(215)	(198)
Other Expenses	(122)	(137)	(424)	(465)
Depreciation, Depletion and Amortization	(333)	(319)	(983)	(930)
Share-based Compensation	(33)	(43)	(120)	(121)
Net Income (Loss) Available to Common Stockholders, Basic	157	143	406	427
Goodwill, Translation Adjustments			12
Corporate and Other [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Assets	126		126		127
Payments to Acquire Productive Assets	33	37	119	116
Adjusted EBITDA by Segment	(238)	(204)	(717)	(654)
North America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Goodwill	7,024		7,024		7,024
Assets	21,094		21,094		20,818
Payments to Acquire Productive Assets	216	245	690	677
Adjusted EBITDA by Segment	817	784	2,441	2,415
Goodwill, Translation Adjustments			0
EMEA [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Goodwill	121		121		109
Assets	1,766		1,766		1,639
Payments to Acquire Productive Assets	25	38	83	117
Adjusted EBITDA by Segment	64	56	189	162
Goodwill, Translation Adjustments			12
Latin America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Goodwill	596		596		596
Assets	2,387		2,387		$ 2,304
Payments to Acquire Productive Assets	48	44	126	118
Adjusted EBITDA by Segment	78	80	235	218
Goodwill, Translation Adjustments			0
Core Network Service [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	1,963	1,929	5,874	5,831
Core Network Service [Member] \| North America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	1,597	1,573	4,798	4,779
Core Network Service [Member] \| EMEA [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	184	180	535	561
Core Network Service [Member] \| Latin America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	182	176	541	491
Wholesale Voice Services [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	96	104	294	309
Wholesale Voice Services [Member] \| North America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	90	98	279	292
Wholesale Voice Services [Member] \| EMEA [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	3	4	8	11
Wholesale Voice Services [Member] \| Latin America [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 3	$ 2	$ 7	$ 6

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

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