Intangible Assets (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended	12 Months Ended
		Mar. 31, 2014	Mar. 31, 2013	Jul. 10, 2013	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013	May. 13, 2016	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Share Price					$ 3.48
Net book value per share price					$ 4.98
Predecessor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of assets and FCC licenses			$ 6	$ 10
Successor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of assets and FCC licenses		$ 1	$ 0		$ 62	$ 315	$ 7
Trademarks [Member] | Successor [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Estimated fair value of Sprint trade name									$ 3,300
Impairment due to Sprint trade name	[1]				$ 0
Subsequent Event [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Share Price								$ 3.44

[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.