Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Current Assets
Cash and Cash Equivalents	$ 3,707	$ 2,641	$ 2,175	$ 4,010	$ 2,175	$ 4,010
Short-term Investments	2,349	0
Accounts and notes receivable, net	1,236	1,099
Device and accessory inventory	1,296	1,173
Prepaid expenses and other current assets	1,984	1,920
Total current assets	10,572	6,833
Investments in Subsidiaries	0	0
Property, plant and equipment, net	19,333	20,297
Due from Affiliate, Noncurrent	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,579	6,575
FCC licenses and other	40,556	40,073
Definite-lived intangible assets, net	3,582	4,469
Other assets	673	728
Total assets	81,295	78,975
Current Liabilities
Accounts Payable, Current	2,894	2,899
Accrued expenses and other current liabilities	4,189	4,374
Current portion of long-term debt, financing and capital lease obligations	6,554	4,690
Total current liabilities	13,637	11,963
Long-term debt, financing and capital lease obligations	30,759	29,268
Deferred tax liabilities	14,238	13,959
Note due to consolidated affiliate	0	0
Other liabilities	3,665	4,002
Due to affiliate	0	0
Total liabilities	62,299	59,192
Commitments and contingencies
Total stockholders' equity	18,996	19,783
Liabilities and Equity	81,295	78,975
Consolidation, Eliminations [Member]
Current Assets
Cash and Cash Equivalents	0	0			0	0
Short-term Investments	0
Accounts and notes receivable, net	(195)	(114)
Device and accessory inventory	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(195)	(114)
Investments in Subsidiaries	(42,920)	(42,912)
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	(13,150)	(19,568)
Note receivable from consolidated affiliate	(10,965)	(10,622)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	0	(1,019)
Total assets	(67,230)	(74,235)
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	(195)	(114)
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	(195)	(114)
Long-term debt, financing and capital lease obligations	0	(1,019)
Deferred tax liabilities	0	0
Note due to consolidated affiliate	(10,965)	(10,622)
Other liabilities	0	0
Due to affiliate	(13,150)	(19,568)
Total liabilities	(24,310)	(31,323)
Total stockholders' equity	(42,920)	(42,912)
Liabilities and Equity	(67,230)	(74,235)
Parent Company [Member]
Current Assets
Cash and Cash Equivalents	0	0			0	0
Short-term Investments	0
Accounts and notes receivable, net	195	87
Device and accessory inventory	0	0
Prepaid expenses and other current assets	0	0
Total current assets	195	87
Investments in Subsidiaries	18,988	19,783
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	25	50
Note receivable from consolidated affiliate	10,390	10,377
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	0	0
Total assets	29,598	30,297
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	212	137
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	212	137
Long-term debt, financing and capital lease obligations	10,390	10,377
Deferred tax liabilities	0	0
Note due to consolidated affiliate	0	0
Other liabilities	0	0
Due to affiliate	0	0
Total liabilities	10,602	10,514
Total stockholders' equity	18,996	19,783
Liabilities and Equity	29,598	30,297
Guarantor Subsidiaries [Member]
Current Assets
Cash and Cash Equivalents	3,117	2,154			1,670	3,492
Short-term Investments	2,329
Accounts and notes receivable, net	1	27
Device and accessory inventory	0	0
Prepaid expenses and other current assets	15	12
Total current assets	5,462	2,193
Investments in Subsidiaries	23,932	23,129
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	13,125	19,518
Note receivable from consolidated affiliate	575	245
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	103	1,127
Total assets	43,197	46,212
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	560	531
Current portion of long-term debt, financing and capital lease obligations	2,583	3,065
Total current liabilities	3,143	3,596
Long-term debt, financing and capital lease obligations	9,773	11,495
Deferred tax liabilities	0	0
Note due to consolidated affiliate	10,390	10,377
Other liabilities	903	961
Due to affiliate	0	0
Total liabilities	24,209	26,429
Total stockholders' equity	18,988	19,783
Liabilities and Equity	43,197	46,212
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Other Additional Capital	600
Current Assets
Cash and Cash Equivalents	590	487			$ 505	$ 518
Short-term Investments	20
Accounts and notes receivable, net	1,235	1,099
Device and accessory inventory	1,296	1,173
Prepaid expenses and other current assets	1,969	1,908
Total current assets	5,110	4,667
Investments in Subsidiaries	0	0
Property, plant and equipment, net	19,333	20,297
Due from Affiliate, Noncurrent	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,579	6,575
FCC licenses and other	40,556	40,073
Definite-lived intangible assets, net	3,582	4,469
Other assets	570	620
Total assets	75,730	76,701
Current Liabilities
Accounts Payable, Current	2,894	2,899
Accrued expenses and other current liabilities	3,612	3,820
Current portion of long-term debt, financing and capital lease obligations	3,971	1,625
Total current liabilities	10,477	8,344
Long-term debt, financing and capital lease obligations	10,596	8,415
Deferred tax liabilities	14,238	13,959
Note due to consolidated affiliate	575	245
Other liabilities	2,762	3,041
Due to affiliate	13,150	19,568
Total liabilities	51,798	53,572
Total stockholders' equity	23,932	23,129
Liabilities and Equity	$ 75,730	$ 76,701