Acquisitions (Narrative) (Details) item in Millions, customer in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) customer item	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Cash paid for acquisition	$ 9,886,000,000
Goodwill	9,507,000,000		$ 7,166,000,000
Capital Expenditures Integration Activities	99,000,000	$ 101,000,000
Connecticut Operations [Member]
Business Acquisition [Line Items]
Acquisition purchase price					$ 2,018,000,000
Capital Expenditures Integration Activities		23,000,000
Verizon Transaction [Member]
Business Acquisition [Line Items]
Acquisition purchase price	10,540,000,000
Cash paid for acquisition	9,886,000,000
Working Capital and Net Debt Settlement Payments Received	15,000,000
Goodwill	2,341,000,000
Goodwill deductible for income tax purposes	$ 1,912,000,000
Number of voice connections acquired | customer	2.6
Number of broadband connections acquired | item	2.1
Number of video connections acquired | item	1.2
Revenue	$ 2,494,000,000
Operating income	45,000,000
Proceeds from equity issuance			2,750,000,000
Capital Expenditures Integration Activities	99,000,000	$ 78,000,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment	1,378,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	6,315,000,000			$ 7,693,000,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles	1,029,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles	2,189,000,000			$ 1,160,000,000
Business Combination Provisional Information Initial Accounting Incomplete Adjustments Related to Previous Period Depreciation	57,000,000
Business Combination Provisional Information Initial Accounting Incomplete Adjustments Related to Previous Period Amortization	62,000,000
Senior And Subsidiary Unsecured Debt [Member] | Verizon Transaction [Member]
Business Acquisition [Line Items]
Debt Instrument, Face Amount	$ 6,600,000,000		$ 6,600,000,000