Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Apr. 01, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	$ 1,835		$ 1,835			$ 1,813
Depreciation, network and other	1,065	$ 1,021	2,185	$ 2,044
Current Assets
Cash and Cash Equivalents	4,262	5,773	4,262	5,773			$ 6,982		$ 6,659
Short-term Investments	61		61				67
Accounts and notes receivable, net	3,723		3,723				3,554
Due from Affiliate, Current	0		0				0
Device and accessory inventory	963		963				999
Prepaid expenses and other current assets	1,197		1,197			1,178	1,289
Total current assets	10,206		10,206				12,891
Investments in Subsidiaries	0		0				0
Property, plant and equipment, net	20,562		20,562			21,197	21,201
Costs to acquire a customer contract	1,712		1,712				1,559
Operating Lease, Right-of-Use Asset	6,885		6,885			7,358
Due from Consolidated Affiliate	0		0				0
Due from Affiliate, Noncurrent	0		0				0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	4,598		4,598				4,598
FCC licenses and other	41,481		41,481				41,465
Property, plant and equipment	1,413		1,413			1,650	1,769
Other assets	1,071		1,071			1,117	1,118
Total assets	87,928		87,928				84,601
Current Liabilities
Accounts Payable, Current	3,918		3,918				3,961
Accrued expenses and other current liabilities	3,198		3,198			3,419	3,597
Current portion of long-term debt, financing and capital lease obligations	4,101		4,101			4,514	4,557
Due to Affiliate, Current	0		0				0
Total current liabilities	13,052		13,052				12,115
Long-term debt, financing and capital lease obligations	33,268		33,268			35,299	35,366
Operating Lease, Liability, Noncurrent	5,667		5,667			6,263
Note due to consolidated affiliate	0		0				0
Deferred tax liabilities	7,489		7,489			7,602	7,556
Other liabilities	2,555		2,555			$ 2,564	3,437
Due to affiliate	0		0				0
Total liabilities	62,031		62,031				58,474
Commitments and contingencies
Total stockholders' equity	25,850		25,850				26,072
Stockholders' Equity Attributable to Noncontrolling Interest	47		47				55
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,897	28,464	25,897	28,464	$ 26,168		26,127	$ 27,945	26,419
Liabilities and Equity	87,928		87,928				84,601
Depreciation, equipment rentals	1,056	1,181	2,085	2,317
Consolidation, Eliminations [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	0		0
Depreciation, network and other	0	0	0	0
Current Assets
Cash and Cash Equivalents	0	0	0	0			0		0
Short-term Investments	0		0				0
Accounts and notes receivable, net	(316)		(316)				(329)
Due from Affiliate, Current	(424)		(424)				(424)
Device and accessory inventory	0		0				0
Prepaid expenses and other current assets	0		0				0
Total current assets	(740)		(740)				(753)
Investments in Subsidiaries	(42,711)		(42,711)				(43,148)
Property, plant and equipment, net	0		0				0
Costs to acquire a customer contract	0		0				0
Operating Lease, Right-of-Use Asset	0		0
Due from Consolidated Affiliate	(5,505)		(5,505)				(2,706)
Due from Affiliate, Noncurrent	(35,038)		(35,038)				(35,450)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0		0				0
FCC licenses and other	0		0				0
Property, plant and equipment	0		0				0
Other assets	0		0				0
Total assets	(83,994)		(83,994)				(82,057)
Current Liabilities
Accounts Payable, Current	0		0				0
Accrued expenses and other current liabilities	(316)		(316)				(329)
Current portion of long-term debt, financing and capital lease obligations	0		0				0
Due to Affiliate, Current	(424)		(424)				(424)
Total current liabilities	(740)		(740)				(753)
Long-term debt, financing and capital lease obligations	0		0				0
Operating Lease, Liability, Noncurrent	0		0
Note due to consolidated affiliate	(35,038)		(35,038)				(35,450)
Deferred tax liabilities	0		0				0
Other liabilities	0		0				0
Due to affiliate	(5,505)		(5,505)				(2,706)
Total liabilities	(41,283)		(41,283)				(38,909)
Commitments and contingencies
Total stockholders' equity	(42,711)		(42,711)				(43,148)
Stockholders' Equity Attributable to Noncontrolling Interest	0		0				0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(42,711)		(42,711)				(43,148)
Liabilities and Equity	(83,994)		(83,994)				(82,057)
Depreciation, equipment rentals	0	0	0	0
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	0		0
Depreciation, network and other	0	0	0	0
Current Assets
Cash and Cash Equivalents	0	0	0	0			0		0
Short-term Investments	0		0				0
Accounts and notes receivable, net	96		96				96
Due from Affiliate, Current	0		0				0
Device and accessory inventory	0		0				0
Prepaid expenses and other current assets	0		0				0
Total current assets	96		96				96
Investments in Subsidiaries	25,567		25,567				25,785
Property, plant and equipment, net	0		0				0
Costs to acquire a customer contract	0		0				0
Operating Lease, Right-of-Use Asset	0		0
Due from Consolidated Affiliate	290		290				288
Due from Affiliate, Noncurrent	11,895		11,895				11,883
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0		0				0
FCC licenses and other	0		0				0
Property, plant and equipment	0		0				0
Other assets	0		0				0
Total assets	37,848		37,848				38,052
Current Liabilities
Accounts Payable, Current	0		0				0
Accrued expenses and other current liabilities	103		103				97
Current portion of long-term debt, financing and capital lease obligations	0		0				0
Due to Affiliate, Current	0		0				0
Total current liabilities	103		103				97
Long-term debt, financing and capital lease obligations	11,895		11,895				11,883
Operating Lease, Liability, Noncurrent	0		0
Note due to consolidated affiliate	0		0				0
Deferred tax liabilities	0		0				0
Other liabilities	0		0				0
Due to affiliate	0		0				0
Total liabilities	11,998		11,998				11,980
Commitments and contingencies
Total stockholders' equity	25,850		25,850				26,072
Stockholders' Equity Attributable to Noncontrolling Interest	0		0				0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,850		25,850				26,072
Liabilities and Equity	37,848		37,848				38,052
Depreciation, equipment rentals	0	0	0	0
Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	0		0
Depreciation, network and other	0	0	0	0
Current Assets
Cash and Cash Equivalents	3,876	5,256	3,876	5,256			6,605		6,222
Short-term Investments	61		61				67
Accounts and notes receivable, net	220		220				233
Due from Affiliate, Current	424		424				424
Device and accessory inventory	0		0				0
Prepaid expenses and other current assets	9		9				9
Total current assets	4,590		4,590				7,338
Investments in Subsidiaries	17,144		17,144				17,363
Property, plant and equipment, net	0		0				0
Costs to acquire a customer contract	0		0				0
Operating Lease, Right-of-Use Asset	0		0
Due from Consolidated Affiliate	5,215		5,215				2,418
Due from Affiliate, Noncurrent	23,143		23,143				23,567
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	0		0				0
FCC licenses and other	0		0				0
Property, plant and equipment	0		0				0
Other assets	40		40				52
Total assets	50,132		50,132				50,738
Current Liabilities
Accounts Payable, Current	0		0				0
Accrued expenses and other current liabilities	228		228				230
Current portion of long-term debt, financing and capital lease obligations	2,574		2,574				1,373
Due to Affiliate, Current	0		0				0
Total current liabilities	2,802		2,802				1,603
Long-term debt, financing and capital lease obligations	9,105		9,105				10,660
Operating Lease, Liability, Noncurrent	0		0
Note due to consolidated affiliate	11,895		11,895				11,883
Deferred tax liabilities	0		0				0
Other liabilities	763		763				807
Due to affiliate	0		0				0
Total liabilities	24,565		24,565				24,953
Commitments and contingencies
Total stockholders' equity	25,567		25,567				25,785
Stockholders' Equity Attributable to Noncontrolling Interest	0		0				0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,567		25,567				25,785
Liabilities and Equity	50,132		50,132				50,738
Depreciation, equipment rentals	0	0	0	0
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	1,835		1,835
Depreciation, network and other	1,065	1,021	2,185	2,044
Other Additional Capital	31	1,300	31	1,300
Current Assets
Cash and Cash Equivalents	386	517	386	517			377		$ 437
Short-term Investments	0		0				0
Accounts and notes receivable, net	3,723		3,723				3,554
Due from Affiliate, Current	0		0				0
Device and accessory inventory	963		963				999
Prepaid expenses and other current assets	1,188		1,188				1,280
Total current assets	6,260		6,260				6,210
Investments in Subsidiaries	0		0				0
Property, plant and equipment, net	20,562		20,562				21,201
Costs to acquire a customer contract	1,712		1,712				1,559
Operating Lease, Right-of-Use Asset	6,885		6,885
Due from Consolidated Affiliate	0		0				0
Due from Affiliate, Noncurrent	0		0				0
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	4,598		4,598				4,598
FCC licenses and other	41,481		41,481				41,465
Property, plant and equipment	1,413		1,413				1,769
Other assets	1,031		1,031				1,066
Total assets	83,942		83,942				77,868
Current Liabilities
Accounts Payable, Current	3,918		3,918				3,961
Accrued expenses and other current liabilities	3,183		3,183				3,599
Current portion of long-term debt, financing and capital lease obligations	1,527		1,527				3,184
Due to Affiliate, Current	424		424				424
Total current liabilities	10,887		10,887				11,168
Long-term debt, financing and capital lease obligations	12,268		12,268				12,823
Operating Lease, Liability, Noncurrent	5,667		5,667
Note due to consolidated affiliate	23,143		23,143				23,567
Deferred tax liabilities	7,489		7,489				7,556
Other liabilities	1,792		1,792				2,630
Due to affiliate	5,505		5,505				2,706
Total liabilities	66,751		66,751				60,450
Commitments and contingencies
Total stockholders' equity	17,144		17,144				17,363
Stockholders' Equity Attributable to Noncontrolling Interest	47		47				55
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	17,191		17,191				17,418
Liabilities and Equity	83,942		83,942				$ 77,868
Depreciation, equipment rentals	$ 1,056	$ 1,181	$ 2,085	$ 2,317