Intangible Assets (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended			3 Months Ended
	Mar. 31, 2013	Jul. 10, 2013	Dec. 31, 2012	Mar. 31, 2014	Dec. 31, 2012	Mar. 31, 2015		Dec. 31, 2013	Dec. 31, 2014	Mar. 31, 2015	Sep. 30, 2014
Predecessor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of assets and FCC licenses	$ 6,000,000	$ 10,000,000	$ 19,000,000
Successor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of assets and FCC licenses	0			1,000,000	0	315,000,000		7,000,000
Goodwill [Member] | Successor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Projected revenues growth rate									1.50%
Projected revenues, discount rate									8.00%
FCC Licenses [Member] | Successor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of assets and FCC licenses										200,000,000	100,000,000
Trademarks [Member] | Successor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Projected revenues growth rate									1.50%
Projected revenues, discount rate									16.00%
Estimated fair value of Sprint trade name									3,300,000,000
Impairment due to Sprint trade name						$ 1,900,000,000	[1]

[1] Net reduction to trademarks for the year ended March 31, 2015 of approximately $1.9 billion was related to the impairment of the Sprint trade name. See discussion below.