Revenue Recognition - Effects of ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	$ 2,087
Cost of services and products (exclusive of depreciation and amortization)	998
Selling, general and administrative expenses	344
Income tax expense	102
Net income	62
Other current assets	183	$ 117
Other long-term assets, net	96	63
Deferred income taxes, net	249
Members' Equity	18,924	$ 19,254
Impact of 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	0
Cost of services and products (exclusive of depreciation and amortization)	0
Selling, general and administrative expenses	13
Income tax expense	(3)
Net income	(10)
Other current assets	(11)
Other long-term assets, net	(15)
Deferred income taxes, net	3
Members' Equity	(19)
ASC 605 Historical Adjusted Balances
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenues	2,087
Cost of services and products (exclusive of depreciation and amortization)	998
Selling, general and administrative expenses	357
Income tax expense	99
Net income	52
Other current assets	172
Other long-term assets, net	81
Deferred income taxes, net	252
Members' Equity	$ 18,905