Background (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) state	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) state segment	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Mar. 31, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of states in which entity operates | state	14		14
Number of reportable segments | segment			1
Revenue reduction	$ (1,799)	$ (2,028)	$ (3,717)	$ (4,058)
Cost of services and products reduction	(490)	(565)	(963)	(1,147)
Lease income	$ 78	$ 82	$ 157	$ 163
Percent of operating revenue	4.00%	4.00%	4.00%	4.00%
Cumulative adjustment	$ 10,123	$ 10,154	$ 10,123	$ 10,154	$ 10,117
Accounting Standards Update [Extensible List]					us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member
RETAINED EARNINGS (ACCUMULATED DEFICIT)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment	73	104	73	104	$ 67	$ (182)	$ 68		$ (23)
RETAINED EARNINGS (ACCUMULATED DEFICIT) | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative adjustment					$ 3	$ 22		$ 3
Change in Accounting Principle, Universal Service Fund
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue reduction	22	23	47	48
Cost of services and products reduction	$ 22	$ 23	$ 47	$ 48