Segments (Segment Financial Information) (Details) $ in Millions		3 Months Ended		6 Months Ended
		Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) segments	Sep. 30, 2015 USD ($)
Segment Reporting Information [Line Items]
Document Period End Date				Sep. 30, 2016
Number of Reportable Segments | segments				2
Segment Reporting Information, Total Net Operating Revenues		$ 8,247	$ 7,975	$ 16,259	$ 16,002
Revenues		8,247	7,975	16,259	16,002
Segment Operating Expenses		(5,900)	(5,967)	(11,455)	(11,912)
Segment Reporting Information Operating Income or Loss		2,347	2,008	4,804	4,090
Depreciation		1,710	1,412	3,390	2,653
Amortization		(271)	(331)	(558)	(678)
Other Operating Expenses Net	[1]	(256)	267	(127)	260
Operating Income		622	(2)	983	499
Interest Expense		(630)	(542)	(1,245)	(1,084)
Other income, net		(15)	5	(7)	9
Loss (income) before income taxes		(23)	(539)	(269)	(576)
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease				1,706	4,081
Severance and exit costs		5	(25)	(11)	(38)
Loss on disposition of property, plant and equipment					(85)
Gain (Loss) on Contract Termination				96	0
Pension Expense			(59)
Loss Contingency Accrual, Provision			(91)
Loss on Disposition of Property Plant Equipment		111	85	231	85
Wireless [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		7,851	7,516	15,448	15,056
Revenues		7,851	7,516	15,448	15,056
Segment Operating Expenses		(5,528)	(5,537)	(10,685)	(11,003)
Segment Reporting Information Operating Income or Loss		2,323	1,979	4,763	4,053
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease				1,497	3,759
Gain (Loss) on Contract Termination				(113)
Wireline [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		392	455	804	938
Revenues		521	609	1,066	1,239
Segment Operating Expenses		(498)	(580)	(1,024)	(1,201)
Segment Reporting Information Operating Income or Loss		23	29	42	38
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease				51	131
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss			233
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		4	4	7	8
Revenues	[2]	(125)	(150)	(255)	(293)
Segment Operating Expenses		126	150	254	292
Segment Reporting Information Operating Income or Loss		1	0	(1)	(1)
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease				158	191
Lease and severance [Member]
Segment Reporting Information [Line Items]
Severance and exit costs		5	(25)	(11)	(38)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	[3]	0	0	0	0
Intersegment Eliminations [Member] | Wireless [Member]
Segment Reporting Information [Line Items]
Revenues		0	0	0	0
Intersegment Eliminations [Member] | Wireline [Member]
Segment Reporting Information [Line Items]
Revenues		129	154	262	301
Intersegment Eliminations [Member] | Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues		(129)	(154)	(262)	(301)
Trademarks [Member] | Wireless [Member]
Segment Reporting Information [Line Items]
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)			1,900
Other, Net [Member]
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of Intangible Assets		354
Other Operating Income (Expense) [Member] | Wireless [Member]
Segment Reporting Information [Line Items]
Restructuring Reserve, Accrual Adjustment			$ 41
New York sales taxes on receipts from sale of wireless services [Member]
Segment Reporting Information [Line Items]
Loss Contingency Accrual, Provision				$ (180)
Successor [Member]
Segment Reporting Information [Line Items]
Legal Fees					157
Successor [Member] | Other Operating Income (Expense) [Member] | Wireless [Member]
Segment Reporting Information [Line Items]
Restructuring Reserve, Accrual Adjustment					$ 20
State and Local Jurisdiction [Member]
Segment Reporting Information [Line Items]
Loss Contingency, Loss in Period		$ (103)

[1] Other, net for the three and six-month periods ended September 30, 2016 consists of $5 million income and $11 million expense, respectively, of severance and exit costs. In addition, both the three and six-month periods ended September 30, 2016 include a $354 million non-cash gain related to spectrum license exchanges with other carriers and a $103 million charge related to a state tax matter. The six-month period ended September 30, 2016 also includes $113 million of contract termination costs, primarily related to the termination of our pre-existing wholesale arrangement with nTelos, as a result of the Shentel transaction. Losses totaling $111 million and $231 million relating to the write-off of leased devices associated with lease cancellations were excluded from Other, net and included within Wireless segment earnings for the three and six-month periods ended September 30, 2016, respectively. Other, net for the three and six-month periods ended September 30, 2015 consists of $25 million and $38 million, respectively, of severance and exit costs. In addition, both the three and six-month periods ended September 30, 2015 include a $157 million accrual for legal reserves related to various pending legal suits and proceedings and an $85 million loss on disposal of property, plant and equipment related to cell site construction costs that are no longer recoverable as a result of changes in the Company's network plans. In addition, the six-month period ended September 30, 2015 includes $20 million of income resulting from a revision to our estimate of a previously recorded reserve.

[2] Revenues eliminated in consolidation consist primarily of wireline services provided to the Wireless segment for resale to or use by wireless subscribers.

[3] Inter-segment revenues consist primarily of wireline services provided to the Wireless segment for resale to, or use by, wireless subscribers.