Commitments And Contingencies (Narrative) (Details) $ in Millions		9 Months Ended
	Oct. 16, 2016 entity	Sep. 30, 2015 USD ($) entity
Regulatory Commitments [Abstract]
Annual support offered by the Federal Communications Commission		$ 283
Number of households to be serviced under regulatory funded programs		660,000
Number of States in our Territory		28
Unconditional Purchase Obligation [Abstract]
Commitment under the arrangement in 2015		$ 141
Vermont Joint Owners Consortium [Abstract]
Number of utilities forming the Vermont Joint Owners consortium | entity		14
Purchase power obligation (in hundredths)		10.00%
Undiscounted purchase obligation if members of the consortium remained in default for the duration of the contract		$ 24
Subsequent Event [Member]
Regulatory Commitments [Abstract]
Number of carriers with tariff pricing plans under review | entity	4
Minimum [Member]
Commitments And Contingencies [Line Items]
Estimated Future Capital Expenditures For Business Operations		700
Maximum [Member]
Commitments And Contingencies [Line Items]
Estimated Future Capital Expenditures For Business Operations		$ 750