Guarantor Financial Information (CONDENSED CONSOLIDATING STATEMENT OF CASH FLOWS) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended	12 Months Ended			15 Months Ended
	Dec. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Jul. 10, 2013	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2013	Mar. 31, 2014
Cash flows from investing activities:
Proceeds from sale-leaseback transaction	$ 1,100		$ 0	$ 0
Cash flows from financing activities:
Proceeds from sale of future lease receivables		$ 0	0	0		$ 0	$ 0
Cash and cash equivalents, beginning of period					$ 4,010
Cash and cash equivalents, end of period					2,641	4,010
Successor [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		522	(2)		3,897	2,450	(61)
Cash flows from investing activities:
Capital expenditures - network and other		(1,488)	0		(4,680)	(5,422)	(3,847)	$ (1,488)
Capital expenditures - leased devices		0	0		(2,292)	(582)	0
Payments to Acquire Intangible Assets		(152)	0		(98)	(163)	(146)
Reimbursements related to FCC licenses		0	0		0	95	0
Acquisitions, net of cash acquired		0	0		0	0	(14,112)
Investment in Clearwire (including debt securities)		0	0		0	0	0
Proceeds from sales and maturities of short-term investments		920	0		418	3,131	1,715
Purchases of short-term investments		(1,035)	0		(252)	(2,077)	(1,719)
Increase (decrease) due from consolidated affiliate from investing activities		0			0	0	0
Payments to Acquire Businesses and Interest in Affiliates							0
Proceeds from sale of assets and FCC licenses		1	0		62	315	7
Proceeds from sale-leaseback transaction		0	0		1,136	0	0
Intercompany note advance to consolidated affiliate					0	0	0
Proceeds from intercompany note advance to consolidated affiliate					0
Other, net		(2)	0		(29)	(11)	(6)
Net cash used in investing activities		(1,756)	0		(5,735)	(4,714)	(18,108)
Cash flows from financing activities:
Proceeds from debt and financings		0	0		755	1,930	9,500
Repayments of debt, financing and capital lease obligations		(159)	0		(899)	(574)	(3,378)
Proceeds from sale of future lease receivables					600
Debt financing costs		(1)	0		(11)	(87)	(147)
Proceeds from Issuance of Common Stock					10	35	18,567
Intercompany dividends paid to parent					0	0
Increase (decrease) due from/to consolidated affiliates from financing activities		0			0	0	0
Proceeds from Contributions from Parent							0
Intercompany note advance from parent					0	0	0
Repayments of intercompany note advance from parent					0
Other, net		0	0		14	0	(14)
Net cash provided by (used in) financing activities		(160)	0		469	1,304	24,528
Cash and Cash Equivalents, Period Increase (Decrease)		(1,394)	(2)		(1,369)	(960)	6,359
Cash and cash equivalents, beginning of period		6,364	5	5	4,010	4,970	5	5
Cash and cash equivalents, end of period		4,970	3		2,641	4,010	6,364	4,970
Successor [Member] | Parent [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		0			0	0	9
Cash flows from investing activities:
Capital expenditures - network and other		0			0	0	0
Capital expenditures - leased devices					0	0
Payments to Acquire Intangible Assets		0			0	0	0
Reimbursements related to FCC licenses						0
Acquisitions, net of cash acquired							(16,640)
Proceeds from sales and maturities of short-term investments		0			0	0	0
Purchases of short-term investments		0			0	0	0
Increase (decrease) due from consolidated affiliate from investing activities		0			1	0	0
Payments to Acquire Businesses and Interest in Affiliates							(1,900)
Proceeds from sale of assets and FCC licenses		0			0	0	0
Proceeds from sale-leaseback transaction					0
Intercompany note advance to consolidated affiliate					0	(1,481)	(8,861)
Proceeds from intercompany note advance to consolidated affiliate					0
Other, net		0			0	0	0
Net cash used in investing activities		0			1	(1,481)	(27,401)
Cash flows from financing activities:
Proceeds from debt and financings					0	1,500	9,000
Repayments of debt, financing and capital lease obligations		0			0	0	0
Proceeds from sale of future lease receivables					0
Debt financing costs		0			(1)	(21)	(139)
Proceeds from Issuance of Common Stock					0	0	18,540
Intercompany dividends paid to parent					0	0
Increase (decrease) due from/to consolidated affiliates from financing activities		0			0	2	0
Proceeds from Contributions from Parent							0
Intercompany note advance from parent					0	0	0
Repayments of intercompany note advance from parent					0
Other, net					0		(14)
Net cash provided by (used in) financing activities		0			(1)	1,481	27,387
Cash and Cash Equivalents, Period Increase (Decrease)		0			0	0	(5)
Cash and cash equivalents, beginning of period		0	5	5	0	0	5	5
Cash and cash equivalents, end of period		0			0	0	0	0
Successor [Member] | Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		(483)			(1,421)	(750)	(458)
Cash flows from investing activities:
Capital expenditures - network and other		0			0	0	0
Capital expenditures - leased devices					0	0
Payments to Acquire Intangible Assets		0			0	0	0
Reimbursements related to FCC licenses						0
Acquisitions, net of cash acquired							2,528
Proceeds from sales and maturities of short-term investments		920			343	3,061	1,715
Purchases of short-term investments		(1,035)			(197)	(1,987)	(1,719)
Increase (decrease) due from consolidated affiliate from investing activities		(941)			(36)	(2,425)	(7,189)
Payments to Acquire Businesses and Interest in Affiliates							0
Proceeds from sale of assets and FCC licenses		0			0	0	0
Proceeds from sale-leaseback transaction					0
Intercompany note advance to consolidated affiliate					(159)	(343)	0
Proceeds from intercompany note advance to consolidated affiliate					372
Other, net		0			0	0	0
Net cash used in investing activities		(1,056)			323	(1,694)	(4,665)
Cash flows from financing activities:
Proceeds from debt and financings					250	300	0
Repayments of debt, financing and capital lease obligations		0			(500)	0	0
Proceeds from sale of future lease receivables					0
Debt financing costs		(1)			0	(5)	0
Proceeds from Issuance of Common Stock					10	35	27
Intercompany dividends paid to parent					0	0
Increase (decrease) due from/to consolidated affiliates from financing activities		0			0	0	0
Proceeds from Contributions from Parent							1,900
Intercompany note advance from parent					0	1,481	8,861
Repayments of intercompany note advance from parent					0
Other, net					0		0
Net cash provided by (used in) financing activities		(1)			(240)	1,811	10,788
Cash and Cash Equivalents, Period Increase (Decrease)		(1,540)			(1,338)	(633)	5,665
Cash and cash equivalents, beginning of period		5,665	0	0	3,492	4,125	0	0
Cash and cash equivalents, end of period		4,125			2,154	3,492	5,665	4,125
Successor [Member] | Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		1,005			5,551	3,700	388
Cash flows from investing activities:
Capital expenditures - network and other		(1,488)			(4,680)	(5,422)	(3,847)
Capital expenditures - leased devices					(2,292)	(582)
Payments to Acquire Intangible Assets		(152)			(98)	(163)	(146)
Reimbursements related to FCC licenses						95
Acquisitions, net of cash acquired							0
Proceeds from sales and maturities of short-term investments		0			75	70	0
Purchases of short-term investments		0			(55)	(90)	0
Increase (decrease) due from consolidated affiliate from investing activities		0			0	0	0
Payments to Acquire Businesses and Interest in Affiliates							0
Proceeds from sale of assets and FCC licenses		1			62	315	7
Proceeds from sale-leaseback transaction					1,136
Intercompany note advance to consolidated affiliate					0	0	0
Proceeds from intercompany note advance to consolidated affiliate					0
Other, net		(2)			(29)	(11)	(6)
Net cash used in investing activities		(1,641)			(5,881)	(5,788)	(3,992)
Cash flows from financing activities:
Proceeds from debt and financings					505	130	500
Repayments of debt, financing and capital lease obligations		(159)			(399)	(574)	(3,378)
Proceeds from sale of future lease receivables					600
Debt financing costs		0			(10)	(61)	(8)
Proceeds from Issuance of Common Stock					0	0	0
Intercompany dividends paid to parent					(233)	(500)
Increase (decrease) due from/to consolidated affiliates from financing activities		941			35	2,423	7,189
Proceeds from Contributions from Parent							0
Intercompany note advance from parent					159	343	0
Repayments of intercompany note advance from parent					(372)
Other, net					14		0
Net cash provided by (used in) financing activities		782			299	1,761	4,303
Cash and Cash Equivalents, Period Increase (Decrease)		146			(31)	(327)	699
Cash and cash equivalents, beginning of period		699	0	0	518	845	0	0
Cash and cash equivalents, end of period		845			487	518	699	845
Successor [Member] | Consolidation, Eliminations [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities		0			(233)	(500)	0
Cash flows from investing activities:
Capital expenditures - network and other		0			0	0	0
Capital expenditures - leased devices					0	0
Payments to Acquire Intangible Assets		0			0	0	0
Reimbursements related to FCC licenses						0
Acquisitions, net of cash acquired							0
Proceeds from sales and maturities of short-term investments		0			0	0	0
Purchases of short-term investments		0			0	0	0
Increase (decrease) due from consolidated affiliate from investing activities		941			35	2,425	7,189
Payments to Acquire Businesses and Interest in Affiliates							1,900
Proceeds from sale of assets and FCC licenses		0			0	0	0
Proceeds from sale-leaseback transaction					0
Intercompany note advance to consolidated affiliate					159	1,824	8,861
Proceeds from intercompany note advance to consolidated affiliate					(372)
Other, net		0			0	0	0
Net cash used in investing activities		941			(178)	4,249	17,950
Cash flows from financing activities:
Proceeds from debt and financings					0	0	0
Repayments of debt, financing and capital lease obligations		0			0	0	0
Proceeds from sale of future lease receivables					0
Debt financing costs		0			0	0	0
Proceeds from Issuance of Common Stock					0	0	0
Intercompany dividends paid to parent					233	500
Increase (decrease) due from/to consolidated affiliates from financing activities		(941)			(35)	(2,425)	(7,189)
Proceeds from Contributions from Parent							(1,900)
Intercompany note advance from parent					(159)	(1,824)	(8,861)
Repayments of intercompany note advance from parent					372
Other, net					0		0
Net cash provided by (used in) financing activities		(941)			411	(3,749)	(17,950)
Cash and Cash Equivalents, Period Increase (Decrease)		0			0	0	0
Cash and cash equivalents, beginning of period		0	0	0	0	0	0	0
Cash and cash equivalents, end of period		$ 0			$ 0	$ 0	0	0
Predecessor [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities			940	2,671
Cash flows from investing activities:
Capital expenditures - network and other			(1,381)	(3,140)
Capital expenditures - leased devices			0	0
Payments to Acquire Intangible Assets			(55)	(125)
Reimbursements related to FCC licenses			0	0
Acquisitions, net of cash acquired			0	(4,039)
Investment in Clearwire (including debt securities)			(80)	(308)
Proceeds from sales and maturities of short-term investments			1,281	2,445
Purchases of short-term investments			(926)	(1,221)
Increase (decrease) due from consolidated affiliate from investing activities			0	0
Proceeds from sale of assets and FCC licenses			6	10
Other, net			(3)	(7)
Net cash used in investing activities			(1,158)	(6,385)
Cash flows from financing activities:
Proceeds from debt and financings			204	204
Repayments of debt, financing and capital lease obligations			(59)	(362)
Debt financing costs			(10)	(11)
Proceeds from Issuance of Common Stock			7	60
Increase (decrease) due from/to consolidated affiliates from financing activities			0	0
Other, net			0	0
Net cash provided by (used in) financing activities			142	(109)
Cash and Cash Equivalents, Period Increase (Decrease)			(76)	(3,823)
Cash and cash equivalents, beginning of period			6,351	6,351			6,351	6,351
Cash and cash equivalents, end of period			6,275	2,528
Predecessor [Member] | Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities			(210)	(559)
Cash flows from investing activities:
Capital expenditures - network and other			0	0
Payments to Acquire Intangible Assets			0	0
Acquisitions, net of cash acquired				(4,039)
Investment in Clearwire (including debt securities)			0	0
Proceeds from sales and maturities of short-term investments			1,281	2,445
Purchases of short-term investments			(926)	(1,221)
Increase (decrease) due from consolidated affiliate from investing activities			(236)	(372)
Proceeds from sale of assets and FCC licenses			0	0
Other, net			0	0
Net cash used in investing activities			119	(3,187)
Cash flows from financing activities:
Proceeds from debt and financings			0	0
Repayments of debt, financing and capital lease obligations			0	0
Debt financing costs			(10)	(11)
Proceeds from Issuance of Common Stock			7	60
Increase (decrease) due from/to consolidated affiliates from financing activities			0	0
Net cash provided by (used in) financing activities			(3)	49
Cash and Cash Equivalents, Period Increase (Decrease)			(94)	(3,697)
Cash and cash equivalents, beginning of period			5,218	5,218			5,218	5,218
Cash and cash equivalents, end of period			5,124	1,521
Predecessor [Member] | Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities			1,150	3,230
Cash flows from investing activities:
Capital expenditures - network and other			(1,381)	(3,140)
Payments to Acquire Intangible Assets			(55)	(125)
Acquisitions, net of cash acquired				0
Investment in Clearwire (including debt securities)			(80)	(308)
Proceeds from sales and maturities of short-term investments			0	0
Purchases of short-term investments			0	0
Increase (decrease) due from consolidated affiliate from investing activities			0	0
Proceeds from sale of assets and FCC licenses			6	10
Other, net			(3)	(7)
Net cash used in investing activities			(1,513)	(3,570)
Cash flows from financing activities:
Proceeds from debt and financings			204	204
Repayments of debt, financing and capital lease obligations			(59)	(362)
Debt financing costs			0	0
Proceeds from Issuance of Common Stock			0	0
Increase (decrease) due from/to consolidated affiliates from financing activities			236	372
Net cash provided by (used in) financing activities			381	214
Cash and Cash Equivalents, Period Increase (Decrease)			18	(126)
Cash and cash equivalents, beginning of period			1,133	1,133			1,133	1,133
Cash and cash equivalents, end of period			1,151	1,007
Predecessor [Member] | Consolidation, Eliminations [Member]
Cash flows from operating activities:
Net cash provided by (used in) operating activities			0	0
Cash flows from investing activities:
Capital expenditures - network and other			0	0
Payments to Acquire Intangible Assets			0	0
Acquisitions, net of cash acquired				0
Investment in Clearwire (including debt securities)			0	0
Proceeds from sales and maturities of short-term investments			0	0
Purchases of short-term investments			0	0
Increase (decrease) due from consolidated affiliate from investing activities			236	372
Proceeds from sale of assets and FCC licenses			0	0
Other, net			0	0
Net cash used in investing activities			236	372
Cash flows from financing activities:
Proceeds from debt and financings			0	0
Repayments of debt, financing and capital lease obligations			0	0
Debt financing costs			0	0
Proceeds from Issuance of Common Stock			0	0
Increase (decrease) due from/to consolidated affiliates from financing activities			(236)	(372)
Net cash provided by (used in) financing activities			(236)	(372)
Cash and Cash Equivalents, Period Increase (Decrease)			0	0
Cash and cash equivalents, beginning of period			0	0			$ 0	$ 0
Cash and cash equivalents, end of period			$ 0	$ 0