Fair Value Measurements (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Sep. 30, 2013
Dec. 31, 2014
Dec. 31, 2013
Available number of funds   2  
Sale Of Certificates Of Deposit $ 150.0    
Amount Transfered From Short Term To Available-For-Sale 167.2    
Amount Transferred From Held To Maturity To Available-For-Sale 31.4    
Short-term Investments [Member] | Nextel Brazil [Member]      
Available for sale securities   110.1 418.6
ARGENTINA      
Money Market Funds, at Carrying Value   43.5