ASC 606 Adoption And Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract assets	$ 42		$ 42		$ 40
Long-term contract assets	41		41		37
Short-term contract liabilities	51		51		41
Long-term contract liabilities	25		$ 25		19
Expected customer life			3 years 9 months 18 days
Short-term contract acquisition costs	97		$ 97		87
Long-term contract acquisition costs	126		126		117
Revenue from contract with customers	2,065	$ 2,106	4,167	$ 4,265
Revenue recognized for satisfaction of performance obligations			64
Revenue from contracts with customers, performance obligation	6,336		6,336
Contributions In Aid Of Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue recognized for satisfaction of performance obligations			16
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract cost incurred during the period			72
Amortized deferred costs			53
Short-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract assets	42		42
Short-term Contract With Customer [Member] | Upfront Fees [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract liabilities	13		13
Long-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term contract assets	41		41
Long-term Contract With Customer [Member] | Upfront Fees [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Long-term contract liabilities	9		9
Impact Of Adoption Of ASC 606 [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract acquisition costs	(97)		(97)		87
Revenue from contract with customers	$ (86)		$ (182)
Impact Of Adoption Of 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
Impact Of Adoption Of 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