Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Current assets
Cash and cash equivalents	$ 6,610	$ 2,870
Short-term investments	2,354	5,444
Accounts and notes receivable, net	3,711	4,138
Due from Affiliate, Current	0
Device and accessory inventory	1,003	1,064
Prepaid expenses and other current assets	575	601
Total Current Assets	14,253	14,117
Investment in subsidiaries	0	0
Property, plant and equipment, net	19,925	19,209
Due from consolidated affiliate	0	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,586	6,579	$ 6,575
FCC licenses and other	41,309	40,585
Definite-lived intangible assets, net	2,465	3,320
Other assets	921	1,313
Total assets	85,459	85,123	78,975
Current liabilities
Due to Affiliate, Current	0
Total Current Liabilities	10,800	12,458
Accounts payable	3,409	3,281
Accrued expenses and other current liabilities	3,962	4,141
Current portion of long-term debt, financing and capital lease obligations	3,429	5,036
Long-term debt, financing and capital lease obligations	37,463	35,878
Deferred tax liabilities	7,294	14,416
Note due to consolidated affiliate	0	0
Other liabilities	3,483	3,563
Due to consolidated affiliate	0	0
Total liabilities	59,040	66,315
Total Stockholders' Equity	26,356	18,808	$ 19,783	$ 21,710
Stockholders' Equity Attributable to Noncontrolling Interest	63	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	26,419	18,808
Total Liabilities and Stockholders' equity	85,459	85,123
Consolidation, Eliminations [Member]
Current assets
Cash and cash equivalents	0	0
Short-term investments	0	0
Accounts and notes receivable, net	(347)	(86)
Due from Affiliate, Current	(424)
Device and accessory inventory	0	0
Prepaid expenses and other current assets	0	0
Total Current Assets	(771)	(86)
Investment in subsidiaries	(45,136)	(42,654)
Property, plant and equipment, net	0	0
Due from consolidated affiliate	(595)	(13,057)
Note receivable from consolidated affiliate	(35,878)	(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	(82,380)	(66,766)
Current liabilities
Due to Affiliate, Current	(424)
Total Current Liabilities	(771)	(86)
Accounts payable	0	0
Accrued expenses and other current liabilities	(347)	(86)
Current portion of long-term debt, financing and capital lease obligations	0	0
Long-term debt, financing and capital lease obligations	0	0
Deferred tax liabilities	0	0
Note due to consolidated affiliate	(35,878)	(10,969)
Other liabilities	0	0
Due to consolidated affiliate	(595)	(13,057)
Total liabilities	(37,244)	(24,112)
Total Stockholders' Equity	(45,136)	(42,654)
Stockholders' Equity Attributable to Noncontrolling Interest	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(45,136)
Total Liabilities and Stockholders' equity	(82,380)	(66,766)
Parent [Member]
Current assets
Cash and cash equivalents	0	0
Short-term investments	0	0
Accounts and notes receivable, net	99	86
Due from Affiliate, Current	0
Device and accessory inventory	0	0
Prepaid expenses and other current assets	5	0
Total Current Assets	104	86
Investment in subsidiaries	26,351	18,800
Property, plant and equipment, net	0	0
Due from consolidated affiliate	1	25
Note receivable from consolidated affiliate	11,887	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	38,343	29,305
Current liabilities
Due to Affiliate, Current	0
Total Current Liabilities	100	103
Accounts payable	0	0
Accrued expenses and other current liabilities	100	103
Current portion of long-term debt, financing and capital lease obligations	0	0
Long-term debt, financing and capital lease obligations	11,887	10,394
Deferred tax liabilities	0	0
Note due to consolidated affiliate	0	0
Other liabilities	0	0
Due to consolidated affiliate	0	0
Total liabilities	11,987	10,497
Total Stockholders' Equity	26,356	18,808
Stockholders' Equity Attributable to Noncontrolling Interest	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	26,356
Total Liabilities and Stockholders' equity	38,343	29,305
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	6,222	2,461
Short-term investments	2,354	5,444
Accounts and notes receivable, net	248	1
Due from Affiliate, Current	424
Device and accessory inventory	0	0
Prepaid expenses and other current assets	9	11
Total Current Assets	9,257	7,917
Investment in subsidiaries	18,785	23,854
Property, plant and equipment, net	0	0
Due from consolidated affiliate	0	13,032
Note receivable from consolidated affiliate	23,991	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	185	134
Total assets	52,218	45,512
Current liabilities
Due to Affiliate, Current	0
Total Current Liabilities	2,173	1,834
Accounts payable	0	0
Accrued expenses and other current liabilities	341	478
Current portion of long-term debt, financing and capital lease obligations	1,832	1,356
Long-term debt, financing and capital lease obligations	10,381	13,647
Deferred tax liabilities	0	0
Note due to consolidated affiliate	11,887	10,394
Other liabilities	831	837
Due to consolidated affiliate	595	0
Total liabilities	25,867	26,712
Total Stockholders' Equity	26,351	18,800
Stockholders' Equity Attributable to Noncontrolling Interest	0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	26,351
Total Liabilities and Stockholders' equity	52,218	45,512
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	388	409
Short-term investments	0	0
Accounts and notes receivable, net	3,711	4,137
Due from Affiliate, Current	0
Device and accessory inventory	1,003	1,064
Prepaid expenses and other current assets	561	590
Total Current Assets	5,663	6,200
Investment in subsidiaries	0	0
Property, plant and equipment, net	19,925	19,209
Due from consolidated affiliate	594	0
Note receivable from consolidated affiliate	0	0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	6,586	6,579
FCC licenses and other	41,309	40,585
Definite-lived intangible assets, net	2,465	3,320
Other assets	736	1,179
Total assets	77,278	77,072
Current liabilities
Due to Affiliate, Current	424
Total Current Liabilities	9,298	10,607
Accounts payable	3,409	3,281
Accrued expenses and other current liabilities	3,868	3,646
Current portion of long-term debt, financing and capital lease obligations	1,597	3,680
Long-term debt, financing and capital lease obligations	15,195	11,837
Deferred tax liabilities	7,294	14,416
Note due to consolidated affiliate	23,991	575
Other liabilities	2,652	2,726
Due to consolidated affiliate	0	13,057
Total liabilities	58,430	53,218
Total Stockholders' Equity	18,785	23,854
Stockholders' Equity Attributable to Noncontrolling Interest	63
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	18,848
Total Liabilities and Stockholders' equity	$ 77,278	$ 77,072