Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016
Current Assets
Cash and Cash Equivalents	$ 2,478	$ 2,870	$ 3,780	$ 2,641
Short-term Investments	4,349	5,444
Accounts and notes receivable, net	4,089	4,138
Device and accessory inventory	979	1,064
Prepaid expenses and other current assets	601	601
Total current assets	12,496	14,117
Investments in Subsidiaries	0	0
Property, plant and equipment, net	18,866	19,209
Due from Affiliate, Noncurrent	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,578	6,579
FCC licenses and other	41,074	40,585
Definite-lived intangible assets, net	3,075	3,320
Other assets	1,235	1,313
Total assets	83,324	85,123
Current Liabilities
Accounts Payable, Current	2,616	3,281
Accrued expenses and other current liabilities	3,830	4,141
Current portion of long-term debt, financing and capital lease obligations	5,125	5,036
Total current liabilities	11,571	12,458
Long-term debt, financing and capital lease obligations	34,459	35,878
Deferred tax liabilities	14,701	14,416
Note due to consolidated affiliate	0	0
Other liabilities	3,578	3,563
Due to affiliate	0	0
Total liabilities	64,309	66,315
Commitments and contingencies
Total stockholders' equity	19,015	18,808
Liabilities and Equity	83,324	85,123
Consolidation, Eliminations [Member]
Current Assets
Cash and Cash Equivalents	0	0	0	0
Short-term Investments	0	0
Accounts and notes receivable, net	(195)	(86)
Device and accessory inventory	0	0
Prepaid expenses and other current assets	0	0
Total current assets	(195)	(86)
Investments in Subsidiaries	(43,387)	(42,654)
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	(12,510)	(13,057)
Note receivable from consolidated affiliate	(10,973)	(10,969)
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	(67,065)	(66,766)
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	(195)	(86)
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	(195)	(86)
Long-term debt, financing and capital lease obligations	0	0
Deferred tax liabilities	0	0
Note due to consolidated affiliate	(10,973)	(10,969)
Other liabilities	0	0
Due to affiliate	(12,510)	(13,057)
Total liabilities	(23,678)	(24,112)
Total stockholders' equity	(43,387)	(42,654)
Liabilities and Equity	(67,065)	(66,766)
Parent Company [Member]
Current Assets
Cash and Cash Equivalents	0	0	0	0
Short-term Investments	0	0
Accounts and notes receivable, net	195	86
Device and accessory inventory	0	0
Prepaid expenses and other current assets	0	0
Total current assets	195	86
Investments in Subsidiaries	19,007	18,800
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	24	25
Note receivable from consolidated affiliate	10,398	10,394
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	29,624	29,305
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	211	103
Current portion of long-term debt, financing and capital lease obligations	0	0
Total current liabilities	211	103
Long-term debt, financing and capital lease obligations	10,398	10,394
Deferred tax liabilities	0	0
Note due to consolidated affiliate	0	0
Other liabilities	0	0
Due to affiliate	0	0
Total liabilities	10,609	10,497
Total stockholders' equity	19,015	18,808
Liabilities and Equity	29,624	29,305
Guarantor Subsidiaries [Member]
Current Assets
Cash and Cash Equivalents	2,034	2,461	3,338	2,154
Short-term Investments	4,349	5,444
Accounts and notes receivable, net	0	1
Device and accessory inventory	0	0
Prepaid expenses and other current assets	14	11
Total current assets	6,397	7,917
Investments in Subsidiaries	24,380	23,854
Property, plant and equipment, net	0	0
Due from Affiliate, Noncurrent	12,486	13,032
Note receivable from consolidated affiliate	575	575
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0	0
FCC licenses and other	0	0
Definite-lived intangible assets, net	0	0
Other assets	133	134
Total assets	43,971	45,512
Current Liabilities
Accounts Payable, Current	0	0
Accrued expenses and other current liabilities	435	478
Current portion of long-term debt, financing and capital lease obligations	956	1,356
Total current liabilities	1,391	1,834
Long-term debt, financing and capital lease obligations	12,342	13,647
Deferred tax liabilities	0	0
Note due to consolidated affiliate	10,398	10,394
Other liabilities	833	837
Due to affiliate	0	0
Total liabilities	24,964	26,712
Total stockholders' equity	19,007	18,800
Liabilities and Equity	43,971	45,512
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Other Additional Capital	42		563
Current Assets
Cash and Cash Equivalents	444	409	$ 442	$ 487
Short-term Investments	0	0
Accounts and notes receivable, net	4,089	4,137
Device and accessory inventory	979	1,064
Prepaid expenses and other current assets	587	590
Total current assets	6,099	6,200
Investments in Subsidiaries	0	0
Property, plant and equipment, net	18,866	19,209
Due from Affiliate, Noncurrent	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,578	6,579
FCC licenses and other	41,074	40,585
Definite-lived intangible assets, net	3,075	3,320
Other assets	1,102	1,179
Total assets	76,794	77,072
Current Liabilities
Accounts Payable, Current	2,616	3,281
Accrued expenses and other current liabilities	3,379	3,646
Current portion of long-term debt, financing and capital lease obligations	4,169	3,680
Total current liabilities	10,164	10,607
Long-term debt, financing and capital lease obligations	11,719	11,837
Deferred tax liabilities	14,701	14,416
Note due to consolidated affiliate	575	575
Other liabilities	2,745	2,726
Due to affiliate	12,510	13,057
Total liabilities	52,414	53,218
Total stockholders' equity	24,380	23,854
Liabilities and Equity	$ 76,794	$ 77,072