Supplemental Cash Flow Disclosures (Details) (Auction 901 Mobility Funds, USD $) In Millions, unless otherwise specified	Mar. 31, 2014 number
Supplemental cash flow disclosures
FCC auction amount received	$ 13.4
FCC auction number of states won	10
Other assets and deferred charges
Supplemental cash flow disclosures
FCC auction amount received	9.4
Property, plant and equipment, net
Supplemental cash flow disclosures
FCC auction amount received	4.0
Maximum
Supplemental cash flow disclosures
FCC auction amount received	$ 40.1