Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Current Assets
Cash and Cash Equivalents	$ 2,175	$ 4,010	$ 3,455	$ 4,970
Short-term Investments	41	166
Accounts and notes receivable, net	1,033	2,290
Device and accessory inventory	995	1,359
Current deferred tax asset	0	62
Prepaid expenses and other current assets	2,317	1,890
Total current assets	6,561	9,777
Investments in Subsidiaries	0	0
Property, plant and equipment, net	20,645	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	40,052	39,987
Definite-lived intangible assets, net	4,807	5,893
Other assets	911	1,077
Total assets	79,551	83,030
Current Liabilities
Accounts Payable, Current	3,078	4,347
Accrued expenses and other current liabilities	4,474	5,293
Deferred Tax Liabilities, Net, Current	186	0
Current portion of long-term debt, financing and capital lease obligations	3,324	1,300
Total current liabilities	11,062	10,940
Long-term debt, financing and capital lease obligations	30,429	32,531
Deferred tax liabilities	13,773	13,898
Note due to consolidated affiliate	0	0
Other liabilities	3,954	3,951
Due to affiliate	0	0
Total liabilities	$ 59,218	$ 61,320
Commitments and contingencies
Total stockholders' equity	$ 20,333	$ 21,710
Liabilities and Equity	79,551	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	196	84
Device and accessory inventory	0	0
Current deferred tax asset	0	0
Prepaid expenses and other current assets	0	0
Total current assets	196	84
Investments in Subsidiaries	20,333	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	127	139
Total assets	31,206	32,503
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	246	154
Deferred Tax Liabilities, Net, Current	0
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	246	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	127	139
Total liabilities	10,873	10,793
Total stockholders' equity	20,333	21,710
Liabilities and Equity	31,206	32,503
Guarantor Subsidiaries [Member]
Current Assets
Cash and Cash Equivalents	1,670	3,492	2,823	4,125
Short-term Investments	26	146
Accounts and notes receivable, net	6	157
Device and accessory inventory	0	0
Current deferred tax asset	0	0
Prepaid expenses and other current assets	17	13
Total current assets	1,719	3,808
Investments in Subsidiaries	22,524	22,413
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	20,920	20,934
Note receivable from consolidated affiliate	563	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	1,254	1,260
Total assets	46,980	48,873
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	571	625
Deferred Tax Liabilities, Net, Current	0
Current portion of long-term debt, financing and capital lease obligations	2,034	500
Total current liabilities	2,605	1,125
Long-term debt, financing and capital lease obligations	12,594	14,576
Deferred tax liabilities	0	0
Note due to consolidated affiliate	10,500	10,500
Other liabilities	948	960
Due to affiliate	0	0
Total liabilities	26,647	27,161
Total stockholders' equity	20,333	21,712
Liabilities and Equity	46,980	48,873
Non-Guarantor Subsidiaries [Member]
Current Assets
Cash and Cash Equivalents	505	518	632	845
Short-term Investments	15	20
Accounts and notes receivable, net	1,033	2,160
Device and accessory inventory	995	1,359
Current deferred tax asset	0	62
Prepaid expenses and other current assets	2,300	1,877
Total current assets	4,848	5,996
Investments in Subsidiaries	0	0
Property, plant and equipment, net	20,645	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	40,052	39,987
Definite-lived intangible assets, net	4,807	5,893
Other assets	676	836
Total assets	77,603	79,008
Current Liabilities
Accounts Payable, Current	3,078	4,347
Accrued expenses and other current liabilities	3,859	4,625
Deferred Tax Liabilities, Net, Current	186
Current portion of long-term debt, financing and capital lease obligations	1,290	800
Total current liabilities	8,413	9,772
Long-term debt, financing and capital lease obligations	8,354	8,474
Deferred tax liabilities	13,773	13,898
Note due to consolidated affiliate	563	458
Other liabilities	3,006	2,991
Due to affiliate	20,970	21,002
Total liabilities	55,079	56,595
Total stockholders' equity	22,524	22,413
Liabilities and Equity	77,603	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	(202)	(111)
Device and accessory inventory	0	0
Current deferred tax asset	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(202)	(111)
Investments in Subsidiaries	(42,857)	(44,125)
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	(20,970)	(21,002)
Note receivable from consolidated affiliate	(11,063)	(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	(1,146)	(1,158)
Total assets	(76,238)	(77,354)
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	(202)	(111)
Deferred Tax Liabilities, Net, Current	0
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	(202)	(111)
Long-term debt, financing and capital lease obligations	(1,019)	(1,019)
Deferred tax liabilities	0	0
Note due to consolidated affiliate	(11,063)	(10,958)
Other liabilities	0	0
Due to affiliate	(21,097)	(21,141)
Total liabilities	(33,381)	(33,229)
Total stockholders' equity	(42,857)	(44,125)
Liabilities and Equity	$ (76,238)	$ (77,354)