Acquisitions (Narrative) (Details) item in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($)	Mar. 31, 2016 USD ($) item	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Acquisition and integration costs		$ 138,000,000	$ 57,000,000
Capital Expenditures Integration Activities		52,000,000	10,000,000
Connecticut Operations [Member]
Business Acquisition [Line Items]
Cash paid for acquisition				$ 2,018,000,000
Acquisition and integration costs			21,000,000
Acquisition costs			1,000,000
Integration costs			20,000,000
Capital Expenditures Integration Activities			10,000,000
Verizon Transaction [Member]
Business Acquisition [Line Items]
Acquisition purchase price		10,540,000,000
Acquisition and integration costs		138,000,000	36,000,000
Acquisition costs		1,000,000	33,000,000
Integration costs		137,000,000	$ 3,000,000
Capital Expenditures Integration Activities		52,000,000
Interest income		$ 8,000,000
Number of voice connections acquired | item		3.3
Number of broadband connections acquired | item		2.1
Number of video connections acquired | item		1.2
Proceeds from equity issuance	$ 2,750,000,000	$ 8,352,000,000
Senior Unsecured Debt [Member] | Verizon Transaction [Member]
Business Acquisition [Line Items]
Debt Instrument, Face Amount		$ 6,600,000,000