ASC 606 Adoption And Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected customer life	3 years 9 months 18 days
Short-term contract acquisition costs	$ 91		$ 87
Long-term contract acquisition costs	121		117
Revenue from contract with customers	2,102	$ 2,159
Revenue recognized for satisfaction of performance obligations	24
Recognition of reductions to revenue related to discounts and other customer incentives	11
Increase in contract assets, due to new contracts	10
Increase (decrease) in contract liabilities driven by collection and deferral of revenue	29
Revenue from contracts with customers	6,915
Contributions In Aid Of Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue recognized for satisfaction of performance obligations	5
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract cost incurred during the period	33
Amortized deferred costs	25
Short-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract assets	39		40
Short-term contract liabilities	47		41
Short-term Contract With Customer [Member] | Upfront Fees [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract liabilities	13
Long-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term contract assets	37		37
Long-term contract liabilities	19		19
Long-term Contract With Customer [Member] | Upfront Fees [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term contract liabilities	9
Adjustments For ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract acquisition costs	(91)		87
Revenue from contract with customers	$ (96)
Adjustments For ASC 606 [Member] | Short-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract assets			40
Short-term contract liabilities			13
Adjustments For ASC 606 [Member] | Long-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term contract assets			37
Long-term contract liabilities			$ 9