Revenue Recognition - Reported Results Under ASC 606 (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended				10 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Oct. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating Revenue	$ 1,407	$ 2,071	$ 2,010	$ 2,052	$ 2,087	$ 6,870	$ 8,220	$ 8,277	$ 8,173
Cost of services and products (exclusive of depreciation and amortization)	690						3,937
Selling, general and administrative	253						1,354
Interest expense	80						509
Income tax expense	234						196
Net income (loss)	(141)	151	$ 88	$ 40	$ 62		341	284
Other current assets	117	234					234	117
Other long-term assets, net		191					191
Deferred revenue		1,491					1,491
Deferred income tax assets, net		306					306
Member's equity	$ 19,272	17,877					17,877	$ 19,272
Impact of ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating Revenue							(5)
Cost of services and products (exclusive of depreciation and amortization)							0
Selling, general and administrative							52
Interest expense							(9)
Income tax expense							(12)
Net income (loss)							(36)
Other current assets		(33)					(33)
Other long-term assets, net		(31)					(31)
Deferred revenue		(4)					(4)
Deferred income tax assets, net		15					15
Member's equity		(45)					(45)
ASC 605 Historical Adjusted Balances
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating Revenue							8,215
Cost of services and products (exclusive of depreciation and amortization)							3,937
Selling, general and administrative							1,406
Interest expense							500
Income tax expense							184
Net income (loss)							305
Other current assets		201					201
Other long-term assets, net		160					160
Deferred revenue		1,487					1,487
Deferred income tax assets, net		321					321
Member's equity		$ 17,832					$ 17,832