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Debt - Receivables Securitization Agreement (Details) - U.S. Cellular - Receivables securitization facility - USD ($)
Dec. 31, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 200,000,000 $ 200,000,000
Amounts borrowed 0  
Available for pledge as collateral $ 63,000,000