Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014
Current Assets
Cash and Cash Equivalents	$ 1,972	$ 4,010	$ 4,135	$ 4,970
Short-term Investments	103	166
Accounts and notes receivable, net	1,980	2,290
Device and accessory inventory	889	1,359
Current deferred tax asset	63	62
Prepaid expenses and other current assets	2,089	1,890
Total current assets	7,096	9,777
Investments in Subsidiaries	0	0
Property, plant and equipment, net	21,061	19,721
Due from Affiliate, Noncurrent	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,575	6,575
FCC licenses and other	40,025	39,987
Definite-lived intangible assets, net	5,155	5,893
Other assets	939	1,077
Total assets	80,851	83,030
Current Liabilities
Accounts Payable, Current	3,527	4,347
Accrued expenses and other current liabilities	4,333	5,293
Current portion of long-term debt, financing and capital lease obligations	1,395	1,300
Total current liabilities	9,255	10,940
Long-term debt, financing and capital lease obligations	32,570	32,531
Deferred tax liabilities	13,929	13,898
Note due to consolidated affiliate	0	0
Other liabilities	3,940	3,951
Due to affiliate	0	0
Total liabilities	$ 59,694	$ 61,320
Commitments and contingencies
Total stockholders' equity	$ 21,157	$ 21,710
Liabilities and Equity	80,851	83,030
Parent Company [Member]
Current Assets
Cash and Cash Equivalents	0	0	0	0
Short-term Investments	0	0
Accounts and notes receivable, net	87	84
Device and accessory inventory	0	0
Current deferred tax asset	0	0
Prepaid expenses and other current assets	0	0
Total current assets	87	84
Investments in Subsidiaries	21,159	21,712
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	50	68
Note receivable from consolidated affiliate	10,500	10,500
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	132	139
Total assets	31,928	32,503
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	139	154
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	139	154
Long-term debt, financing and capital lease obligations	10,500	10,500
Deferred tax liabilities	0	0
Note due to consolidated affiliate	0	0
Other liabilities	0	0
Due to affiliate	132	139
Total liabilities	10,771	10,793
Total stockholders' equity	21,157	21,710
Liabilities and Equity	31,928	32,503
Guarantor Subsidiaries [Member]
Current Assets
Cash and Cash Equivalents	1,513	3,492	3,488	4,125
Short-term Investments	103	146
Accounts and notes receivable, net	67	157
Device and accessory inventory	0	0
Current deferred tax asset	0	0
Prepaid expenses and other current assets	14	13
Total current assets	1,697	3,808
Investments in Subsidiaries	22,442	22,413
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	22,226	20,934
Note receivable from consolidated affiliate	459	458
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	1,255	1,260
Total assets	48,079	48,873
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	523	625
Current portion of long-term debt, financing and capital lease obligations	500	500
Total current liabilities	1,023	1,125
Long-term debt, financing and capital lease obligations	14,446	14,576
Deferred tax liabilities	0	0
Note due to consolidated affiliate	10,500	10,500
Other liabilities	951	960
Due to affiliate	0	0
Total liabilities	26,920	27,161
Total stockholders' equity	21,159	21,712
Liabilities and Equity	48,079	48,873
Non-Guarantor Subsidiaries [Member]
Current Assets
Cash and Cash Equivalents	459	518	647	845
Short-term Investments	0	20
Accounts and notes receivable, net	1,980	2,160
Device and accessory inventory	889	1,359
Current deferred tax asset	63	62
Prepaid expenses and other current assets	2,075	1,877
Total current assets	5,466	5,996
Investments in Subsidiaries	0	0
Property, plant and equipment, net	21,061	19,721
Due from Affiliate, Noncurrent	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,575	6,575
FCC licenses and other	40,025	39,987
Definite-lived intangible assets, net	5,155	5,893
Other assets	703	836
Total assets	78,985	79,008
Current Liabilities
Accounts Payable, Current	3,527	4,347
Accrued expenses and other current liabilities	3,825	4,625
Current portion of long-term debt, financing and capital lease obligations	895	800
Total current liabilities	8,247	9,772
Long-term debt, financing and capital lease obligations	8,643	8,474
Deferred tax liabilities	13,929	13,898
Note due to consolidated affiliate	459	458
Other liabilities	2,989	2,991
Due to affiliate	22,276	21,002
Total liabilities	56,543	56,595
Total stockholders' equity	22,442	22,413
Liabilities and Equity	78,985	79,008
Consolidation, Eliminations [Member]
Current Assets
Cash and Cash Equivalents	0	0	$ 0	$ 0
Short-term Investments	0	0
Accounts and notes receivable, net	(154)	(111)
Device and accessory inventory	0	0
Current deferred tax asset	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(154)	(111)
Investments in Subsidiaries	(43,601)	(44,125)
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	(22,276)	(21,002)
Note receivable from consolidated affiliate	(10,959)	(10,958)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	(1,151)	(1,158)
Total assets	(78,141)	(77,354)
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	(154)	(111)
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	(154)	(111)
Long-term debt, financing and capital lease obligations	(1,019)	(1,019)
Deferred tax liabilities	0	0
Note due to consolidated affiliate	(10,959)	(10,958)
Other liabilities	0	0
Due to affiliate	(22,408)	(21,141)
Total liabilities	(34,540)	(33,229)
Total stockholders' equity	(43,601)	(44,125)
Liabilities and Equity	$ (78,141)	$ (77,354)