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Stock-Based Compensation - U.S. Cellular, Overview and Valuation model (Details) - Common Shares - shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2016
U.S. Cellular Long-Term Incentive Plans | Stock Options    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Remaining contractual term 10 years  
Award vesting period 3 years  
Expiration period 30 days  
Black Scholes valuation model assumptions    
Expected life   4 years 8 months 12 days
Expected annual volatility rate   30.50%
Dividend yield   0.00%
Risk-free interest rate   1.20%
Estimated annual forfeiture rate   9.40%
U.S. Cellular Long-Term Incentive Plans | Stock Options | Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Exercisable term 90 days  
U.S. Cellular Long-Term Incentive Plans | Stock Options | Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Exercisable term 1 year  
U.S. Cellular | U.S. Cellular Long-Term Incentive Plans    
Stock-based compensation, overview    
Shares reserved 13,286,000  
U.S. Cellular | Non-Employee Directors' Plan    
Stock-based compensation, overview    
Shares reserved 137,000