Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Mar. 31, 2013	Jul. 10, 2013	Mar. 31, 2016	Mar. 31, 2015		Dec. 31, 2013	Nov. 19, 2015
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property						$ 487
Gain (Loss) on Disposition of Property Plant Equipment	$ 65
Capital Expenditures Incurred but Not yet Paid									$ 2,400
Sale Leaseback Transaction, Net Book Value	$ 1,300					1,200				$ 1,300
Asset impairments						166
Depreciation						1,800	$ 206
Predecessor [Member]
Property, Plant and Equipment [Line Items]
Asset impairments				$ 0	$ 0
Depreciation				1,422	$ 3,098
Successor [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property			$ (75)
Capital Expenditures Incurred but Not yet Paid			2,000			468	1,500
Asset impairments			0	0		0	2,133	[1]	0
Depreciation			868	$ 0		5,794	3,797		$ 2,026
Wireline [Member]
Property, Plant and Equipment [Line Items]
Estimated fair value		$ 918
Wireline [Member] | Successor [Member]
Property, Plant and Equipment [Line Items]
Impairment loss		$ 233
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property						256
Gain (Loss) on Disposition of Property Plant Equipment						65
Increase (decrease) in device and accessory inventory						3,200	1,200
Increase in accounts payable						159	$ 182
Leased devices [Member] | Wireless [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property						321
Network Equipment, Site Costs and Related Software [Member]
Property, Plant and Equipment [Line Items]
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property			$ 75			$ 166

[1] (2)Impairments for the Successor year ended March 31, 2015 consist of a $1.9 billion trade name impairment related to the Wireless segment and a $233 million impairment related to Wireline long-lived assets.