Revenue Recognition - Additional Information - Overview (Details) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($) category	Mar. 31, 2020 USD ($)
Revenue from Contract with Customer [Abstract]
Number of categories of products and services \| category	4
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1,792	$ 1,918
Voice and Other - CAF Phase II [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 36

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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+ Details