Background (Details) $ in Millions		3 Months Ended
		Mar. 31, 2020 USD ($) state segment	Mar. 31, 2019 USD ($)	Jan. 01, 2020 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of states in which entity operates | state		14
Number of reportable segments | segment		1
Revenue reduction	[1]	$ (1,918)	$ (2,030)
Cost of services and products reduction	[1]	(473)	(582)
Lease income		$ 79	$ 81
Percent of operating revenue		4.00%	4.00%
RETAINED EARNINGS (ACCUMULATED DEFICIT) | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative net effect of adoption of ASU				$ 3
Change in Accounting Principle, Universal Service Fund
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue reduction		$ 25	$ 25
Cost of services and products reduction		$ 25	$ 25

[1] Reclassifications were made within certain 2019 comparative figures due to the retrospective application of an accounting policy election during the first quarter of 2020. Refer to Note 1—Background and our Form 8-K filing dated May 7, 2020 for further information.