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Stock-Based Compensation, U.S. Cellular, Overview and Valuation model (Details) - U.S. Cellular - shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
U.S. Cellular Long-Term Incentive Plans      
Stock-based compensation, overview      
Description of awards Under the U.S. Cellular Long-Term Incentive Plans, U.S. Cellular may grant fixed and performance based incentive and non-qualified stock options, restricted stock, restricted stock units, and deferred compensation stock unit awards to key employees. At December 31, 2017, the only types of awards outstanding are fixed non-qualified stock option awards, restricted stock unit awards, performance share awards and deferred compensation stock unit awards.    
U.S. Cellular Long-Term Incentive Plans | Stock Options | Minimum      
Stock-based compensation, overview      
Stock options expiration date Apr. 01, 2018    
U.S. Cellular Long-Term Incentive Plans | Stock Options | Maximum      
Stock-based compensation, overview      
Stock options expiration date Apr. 01, 2026    
U.S. Cellular Long-Term Incentive Plans | Deferred Compensation Stock Units      
Stock-based compensation, overview      
Description of awards Certain U.S. Cellular employees may elect to defer receipt of all or a portion of their annual bonuses and to receive a company matching contribution on the amount deferred. All bonus compensation that is deferred by employees electing to participate is immediately vested and is deemed to be invested in U.S. Cellular Common Share stock units. The amount of U.S. Cellular’s matching contribution depends on the portion of the annual bonus that is deferred. Participants receive a 25% match for amounts deferred up to 50% of their total annual bonus and a 33% match for amounts that exceed 50% of their total annual bonus; such matching contributions also are deemed to be invested in U.S. Cellular Common Share stock units and vest over three years.    
U.S. Cellular Common Shares | U.S. Cellular Long-Term Incentive Plans      
Stock-based compensation, overview      
Shares reserved 14,449,000    
U.S. Cellular Common Shares | U.S. Cellular Long-Term Incentive Plans | Stock Options      
Black Scholes valuation model assumptions      
Expected life   4 years 8 months 4 years 7 months
Expected annual volatility rate   30.50% 30.10%
Dividend yield   0.00% 0.00%
Risk-free interest rate   1.20% 1.20%
Risk-free interest rate, minimum     1.20%
Estimated annual forfeiture rate   9.40% 9.70%
U.S. Cellular Common Shares | Non-Employee Directors' Plan      
Stock-based compensation, overview      
Shares reserved 154,000