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Fair Value Measurements (Tables)
3 Months Ended
Mar. 31, 2021
Fair Value Disclosures [Abstract]  
Fair value measurements
TDS has applied the provisions of fair value accounting for purposes of computing the fair value of financial instruments for disclosure purposes as displayed below.
 Level within the Fair Value HierarchyMarch 31, 2021December 31, 2020
 Book ValueFair ValueBook ValueFair Value
(Dollars in millions)     
Long-term debt
Retail2$2,753 $2,814 $2,753 $2,809 
Institutional2535 661 535 707 
Other2796 796 230 230