Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Current assets
Cash and cash equivalents	$ 6,982		$ 6,610
Short-term investments	67		2,354
Accounts and notes receivable, net	3,554	$ 3,808	3,711
Due from Affiliate, Current	0		0
Device and accessory inventory	999	979	1,003
Prepaid expenses and other current assets	1,289	846	575
Total Current Assets	12,891		14,253
Investment in subsidiaries	0		0
Property, plant and equipment, net	21,201		19,925
Capitalized Contract Cost, Net	1,559	1,219
Due from consolidated affiliate	0		0
Note receivable from consolidated affiliate	0		0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	4,598		6,586	$ 6,579
FCC licenses and other	41,465		41,309
Definite-lived intangible assets, net	1,769		2,465
Other assets	1,118	964	921
Total assets	84,601		85,459	85,123
Current liabilities
Due to Affiliate, Current	0		0
Total Current Liabilities	12,115		10,800
Accounts payable	3,961		3,409
Accrued expenses and other current liabilities	3,597	3,927	3,962
Current portion of long-term debt, financing and capital lease obligations	4,557		3,429
Long-term debt, financing and capital lease obligations	35,366		37,463
Deferred tax liabilities	7,556	7,660	7,294
Note due to consolidated affiliate	0		0
Other liabilities	3,437	$ 3,451	3,483
Due to consolidated affiliate	0		0
Total liabilities	58,474		59,040
Total Stockholders' Equity	26,072		26,356	$ 18,808	$ 19,783
Stockholders' Equity Attributable to Noncontrolling Interest	55		63
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	26,127		26,419
Total Liabilities and Stockholders' equity	84,601		85,459
Consolidation, Eliminations [Member]
Current assets
Cash and cash equivalents	0		0
Short-term investments	0		0
Accounts and notes receivable, net	(329)		(347)
Due from Affiliate, Current	(424)		(424)
Device and accessory inventory	0		0
Prepaid expenses and other current assets	0		0
Total Current Assets	(753)		(771)
Investment in subsidiaries	(43,148)		(45,136)
Property, plant and equipment, net	0		0
Capitalized Contract Cost, Net	0
Due from consolidated affiliate	(2,706)		(595)
Note receivable from consolidated affiliate	(35,450)		(35,878)
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	(82,057)		(82,380)
Current liabilities
Due to Affiliate, Current	(424)		(424)
Total Current Liabilities	(753)		(771)
Accounts payable	0		0
Accrued expenses and other current liabilities	(329)		(347)
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	(35,450)		(35,878)
Other liabilities	0		0
Due to consolidated affiliate	(2,706)		(595)
Total liabilities	(38,909)		(37,244)
Total Stockholders' Equity	(43,148)		(45,136)
Stockholders' Equity Attributable to Noncontrolling Interest	0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(43,148)		(45,136)
Total Liabilities and Stockholders' equity	(82,057)		(82,380)
Parent [Member]
Current assets
Cash and cash equivalents	0		0
Short-term investments	0		0
Accounts and notes receivable, net	96		99
Due from Affiliate, Current	0		0
Device and accessory inventory	0		0
Prepaid expenses and other current assets	0		5
Total Current Assets	96		104
Investment in subsidiaries	25,785		26,351
Property, plant and equipment, net	0		0
Capitalized Contract Cost, Net	0
Due from consolidated affiliate	288		1
Note receivable from consolidated affiliate	11,883		11,887
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	38,052		38,343
Current liabilities
Due to Affiliate, Current	0		0
Total Current Liabilities	97		100
Accounts payable	0		0
Accrued expenses and other current liabilities	97		100
Current portion of long-term debt, financing and capital lease obligations	0		0
Long-term debt, financing and capital lease obligations	11,883		11,887
Deferred tax liabilities	0		0
Note due to consolidated affiliate	0		0
Other liabilities	0		0
Due to consolidated affiliate	0		0
Total liabilities	11,980		11,987
Total Stockholders' Equity	26,072		26,356
Stockholders' Equity Attributable to Noncontrolling Interest	0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	26,072		26,356
Total Liabilities and Stockholders' equity	38,052		38,343
Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	6,605		6,222
Short-term investments	67		2,354
Accounts and notes receivable, net	233		248
Due from Affiliate, Current	424		424
Device and accessory inventory	0		0
Prepaid expenses and other current assets	9		9
Total Current Assets	7,338		9,257
Investment in subsidiaries	17,363		18,785
Property, plant and equipment, net	0		0
Capitalized Contract Cost, Net	0
Due from consolidated affiliate	2,418		0
Note receivable from consolidated affiliate	23,567		23,991
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0		0
FCC licenses and other	0		0
Definite-lived intangible assets, net	0		0
Other assets	52		185
Total assets	50,738		52,218
Current liabilities
Due to Affiliate, Current	0		0
Total Current Liabilities	1,603		2,173
Accounts payable	0		0
Accrued expenses and other current liabilities	230		341
Current portion of long-term debt, financing and capital lease obligations	1,373		1,832
Long-term debt, financing and capital lease obligations	10,660		10,381
Deferred tax liabilities	0		0
Note due to consolidated affiliate	11,883		11,887
Other liabilities	807		831
Due to consolidated affiliate	0		595
Total liabilities	24,953		25,867
Total Stockholders' Equity	25,785		26,351
Stockholders' Equity Attributable to Noncontrolling Interest	0		0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,785		26,351
Total Liabilities and Stockholders' equity	50,738		52,218
Non-Guarantor Subsidiaries [Member]
Current assets
Cash and cash equivalents	377		388
Short-term investments	0		0
Accounts and notes receivable, net	3,554		3,711
Due from Affiliate, Current	0		0
Device and accessory inventory	999		1,003
Prepaid expenses and other current assets	1,280		561
Total Current Assets	6,210		5,663
Investment in subsidiaries	0		0
Property, plant and equipment, net	21,201		19,925
Capitalized Contract Cost, Net	1,559
Due from consolidated affiliate	0		594
Note receivable from consolidated affiliate	0		0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	4,598		6,586
FCC licenses and other	41,465		41,309
Definite-lived intangible assets, net	1,769		2,465
Other assets	1,066		736
Total assets	77,868		77,278
Current liabilities
Due to Affiliate, Current	424		424
Total Current Liabilities	11,168		9,298
Accounts payable	3,961		3,409
Accrued expenses and other current liabilities	3,599		3,868
Current portion of long-term debt, financing and capital lease obligations	3,184		1,597
Long-term debt, financing and capital lease obligations	12,823		15,195
Deferred tax liabilities	7,556		7,294
Note due to consolidated affiliate	23,567		23,991
Other liabilities	2,630		2,652
Due to consolidated affiliate	2,706		0
Total liabilities	60,450		58,430
Total Stockholders' Equity	17,363		18,785
Stockholders' Equity Attributable to Noncontrolling Interest	55		63
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	17,418		18,848
Total Liabilities and Stockholders' equity	$ 77,868		$ 77,278