ASC 606 Adoption And Revenue Recognition (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract assets	$ 38		$ 38		$ 40
Long-term contract assets	37		37		37
Short-term contract liabilities	45		45		41
Long-term contract liabilities	$ 28		$ 28		19
Expected customer life	3 years 9 months 18 days		3 years 9 months 18 days
Short-term contract acquisition costs	$ 102		$ 102		87
Long-term contract acquisition costs	128		128		117
Revenue from contract with customers	2,031	$ 2,060	6,198	$ 6,325
Revenue recognized for satisfaction of performance obligations			90
Revenue from contracts with customers, performance obligation	5,941		5,941
Contributions In Aid Of Construction [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue recognized for satisfaction of performance obligations			26
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Capitalized contract cost incurred during the period			106
Amortized deferred costs			80
Short-term Contract With Customer [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Short-term contract assets	38		38
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	37		37
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	(102)		(102)		87
Revenue from contract with customers	$ (84)		$ (266)
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