Income Taxes (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended		12 Months Ended
		Dec. 31, 2014	Mar. 31, 2014	Mar. 31, 2013	Jul. 10, 2013	Jul. 09, 2013	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount								$ 272
Income tax expense					$ 1,600
FCC license amortization period for tax purposes (in years)							15 years
Deferred tax assets, operating loss carryforwards, domestic							$ 6,900
Deferred tax assets, operating loss carryforwards, state and local							969
Deferred tax assets, operating loss carryforwards, foreign							273
Capital loss carryforward							217
Deferred tax assets, capital loss carryforwards							83	84
Deferred tax assets, tax credit carryforwards							459
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, upper bound							20
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							155
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							19,600
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							20,800
Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							821
Federal AMT [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							20,600
State AMT [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							4,800
Successor [Member]
Income Tax Contingency [Line Items]
Change in valuation allowance			$ 82	$ 0			939	911	$ 708
Income tax expense			56	1			141	(574)	45
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount			0	0			(90)	0	0
Gain on previously-held equity interests			0	0			0	0	0
Income (loss) from continuing operations before income taxes, foreign			110				343	398	$ 263
Unrecognized tax benefit			$ 160				166	$ 163
Predecessor [Member]
Income Tax Contingency [Line Items]
Change in valuation allowance				265	1,410
Income tax expense				38	1,601
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount				0	0
Gain on previously-held equity interests				0	(2,926)
Income (loss) from continuing operations before income taxes, foreign				$ 96	$ 238
Clearwire [Member] | Predecessor [Member]
Income Tax Contingency [Line Items]
Gain on previously-held equity interests						$ (2,900)
Expire prior to 2017 [Member]
Income Tax Contingency [Line Items]
Capital loss carryforward							213
Deferred tax assets, tax credit carryforwards							3
Expire between 2017 and 2018 [Member]
Income Tax Contingency [Line Items]
Capital loss carryforward							4
Expiration Between 2016 and 2020 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							1,100
Expiration Between 2021 and 2034 [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							18,500
No Expiration [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards							102
No Expiration [Member] | Foreign Tax Authority [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards							427
Expire Between 2016 and 2034 [Member] [Member]
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards							354
Trademarks [Member] | Successor [Member]
Income Tax Contingency [Line Items]
Impairment of intangible assets, indefinite-lived (excluding goodwill)	[1]						$ 0
Wireless [Member] | Trademarks [Member] | Successor [Member]
Income Tax Contingency [Line Items]
Impairment of intangible assets, indefinite-lived (excluding goodwill)		$ 1,900

[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.