Schedule II - Consolidated Valuation And Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule II - Consolidated Valuation And Qualifying Accounts [Abstract]
Allowance for uncollectible accounts, Balance at Beginning of Period	[1]	$ 54	$ 66	$ 80
Allowance for uncollectible accounts, Charged to Costs and Expenses	[1]	50	43	41
Allowance for uncollectible accounts, Deductions	[1],[2]	46	55	55
Allowance for uncollectible accounts, Balance at End of Period	[1]	$ 58	$ 54	$ 66

[1] Allowance for uncollectible accounts is deducted from Accounts receivable - Customers.

[2] Deductions consist principally of write-offs, net of collections of receivables previously written off.