Background (Details) $ in Millions		3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 01, 2020	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018
Accounting Policies [Abstract]
Number of reportable segments | segment					1
New Accounting Pronouncement, Early Adoption [Line Items]
Cost of services and products reduction			$ (890)	$ (831)	$ (1,766)	$ (1,702)
Revenue reduction			(1,984)	(1,926)	(3,964)	(3,876)
Rental income			$ 192	$ 51	$ 368	$ 101
Percent of operating revenue			10.00%	3.00%	9.00%	3.00%
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member						us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
Member's equity			$ (12,902)	$ (13,793)	$ (12,902)	$ (13,793)	$ (13,545)
Dividends declared					850
Forecast
New Accounting Pronouncement, Early Adoption [Line Items]
Dividends declared		$ 175
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
New Accounting Pronouncement, Early Adoption [Line Items]
Member's equity							$ 3
Change in Accounting Principle, Universal Service Fund
New Accounting Pronouncement, Early Adoption [Line Items]
Cost of services and products reduction			92	88	188	184
Revenue reduction			$ 92	$ 88	$ 188	$ 184