Acquisitions (Narrative) (Details) item in Millions		1 Months Ended	3 Months Ended								12 Months Ended
	Apr. 01, 2016 USD ($) item	Oct. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition, Date of Acquisition [Abstract]
Cash paid for acquisition											$ 9,871,000,000
Goodwill			$ 9,674,000,000				$ 7,166,000,000				9,674,000,000	$ 7,166,000,000	$ 7,205,000,000
Revenue			2,409,000,000	$ 2,524,000,000	$ 2,608,000,000	$ 1,355,000,000	1,413,000,000	$ 1,424,000,000	$ 1,368,000,000	$ 1,371,000,000	8,896,000,000	5,576,000,000	4,772,000,000
Operating income			255,000,000	$ 264,000,000	$ 311,000,000	$ 58,000,000	182,000,000	207,000,000	$ 193,000,000	$ 163,000,000	888,000,000	745,000,000	820,000,000
Capital Expenditures Integration Activities											142,000,000	153,000,000	116,000,000
Proceeds from equity issuance												2,750,000,000
Restricted cash							8,444,000,000					8,444,000,000
Verizon Transaction
Business Acquisition, Date of Acquisition [Abstract]
Acquisition purchase price	$ 10,540,000,000
Working Capital And Net Debt Settlement Payments Received		$ 15,000,000
Number of video connections acquired | item	1.2
Number of broadband connections acquired | item	2.1
Number of voice connections acquired | item	2.5
Cash paid for acquisition	$ 9,886,000,000
Goodwill			$ 2,508,000,000								2,508,000,000
Revenue											3,622,000,000
Operating income											582,000,000
Capital Expenditures Integration Activities											$ 142,000,000	129,000,000
Verizon Transaction | Senior Unsecured Debt [Member]
Business Acquisition, Date of Acquisition [Abstract]
Debt instrument, face amount							6,600,000,000	$ 6,600,000,000				6,600,000,000
Connecticut Transaction
Business Acquisition, Date of Acquisition [Abstract]
Cash paid for acquisition													2,018,000,000
Goodwill							815,000,000					815,000,000
Goodwill deductible for income tax purposes							$ 75,000,000					75,000,000
Revenue												1,049,000,000	216,000,000
Operating income												100,000,000	38,000,000
Capital Expenditures Integration Activities												$ 24,000,000	$ 116,000,000