Guarantor Financial Information (CONDENSED CONSOLIDATING BALANCE SHEET) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Apr. 01, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	$ 1,860		$ 1,860				$ 1,813
Depreciation, network and other	1,071	$ 1,088	3,256	$ 3,132
Current Assets
Cash and Cash Equivalents	3,179	6,285	3,179	6,285				$ 6,982			$ 6,659
Short-term Investments	62		62					67
Accounts and notes receivable, net	3,873		3,873					3,554
Due from Affiliate, Current	0		0					0
Device and accessory inventory	1,117		1,117					999
Prepaid expenses and other current assets	1,224		1,224				1,178	1,289
Total current assets	9,455		9,455					12,891
Investments in Subsidiaries	0		0					0
Property, plant and equipment, net	20,827		20,827				21,197	21,201
Costs to acquire a customer contract	1,808		1,808					1,559
Operating Lease, Right-of-Use Asset	6,713		6,713				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	41,492		41,492					41,465
Property, plant and equipment	918		918				1,650	1,769
Other assets	1,091		1,091				1,117	1,118
Total assets	86,902		86,902					84,601
Current Liabilities
Accounts Payable, Current	3,396		3,396					3,961
Accrued expenses and other current liabilities	3,335		3,335				3,419	3,597
Current portion of long-term debt, financing and capital lease obligations	3,880		3,880				4,514	4,557
Due to Affiliate, Current	0		0					0
Total current liabilities	12,471		12,471					12,115
Long-term debt, financing and capital lease obligations	33,507		33,507				35,299	35,366
Operating Lease, Liability, Noncurrent	5,423		5,423				6,263
Note due to consolidated affiliate	0		0					0
Deferred tax liabilities	7,038		7,038				7,602	7,556
Other liabilities	2,708		2,708				$ 2,564	3,437
Due to affiliate	0		0					0
Total liabilities	61,147		61,147					58,474
Commitments and contingencies
Total stockholders' equity	25,755		25,755					26,072
Stockholders' Equity Attributable to Noncontrolling Interest	0		0					55
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,755	28,329	25,755	28,329	$ 25,897	$ 26,168		26,127	$ 28,464	$ 27,945	26,419
Liabilities and Equity	86,902		86,902					84,601
Depreciation, equipment rentals	1,011	1,137	3,096	3,454
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	(706)		(706)					(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	(1,130)		(1,130)					(753)
Investments in Subsidiaries	(42,492)		(42,492)					(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	(6,399)		(6,399)					(2,706)
Due from Affiliate, Noncurrent	(35,045)		(35,045)					(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	(85,066)		(85,066)					(82,057)
Current Liabilities
Accounts Payable, Current	0		0					0
Accrued expenses and other current liabilities	(706)		(706)					(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	(1,130)		(1,130)					(753)
Long-term debt, financing and capital lease obligations	0		0					0
Operating Lease, Liability, Noncurrent	0		0
Note due to consolidated affiliate	(35,045)		(35,045)					(35,450)
Deferred tax liabilities	0		0					0
Other liabilities	0		0					0
Due to affiliate	(6,399)		(6,399)					(2,706)
Total liabilities	(42,574)		(42,574)					(38,909)
Commitments and contingencies
Total stockholders' equity	(42,492)		(42,492)					(43,148)
Stockholders' Equity Attributable to Noncontrolling Interest	0		0					0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(42,492)		(42,492)					(43,148)
Liabilities and Equity	(85,066)		(85,066)					(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	233		233					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	233		233					96
Investments in Subsidiaries	25,471		25,471					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	11,902		11,902					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	37,896		37,896					38,052
Current Liabilities
Accounts Payable, Current	0		0					0
Accrued expenses and other current liabilities	239		239					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	239		239					97
Long-term debt, financing and capital lease obligations	11,902		11,902					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	12,141		12,141					11,980
Commitments and contingencies
Total stockholders' equity	25,755		25,755					26,072
Stockholders' Equity Attributable to Noncontrolling Interest	0		0					0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,755		25,755					26,072
Liabilities and Equity	37,896		37,896					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	2,932	5,800	2,932	5,800				6,605			6,222
Short-term Investments	62		62					67
Accounts and notes receivable, net	473		473					233
Due from Affiliate, Current	424		424					424
Device and accessory inventory	0		0					0
Prepaid expenses and other current assets	15		15					9
Total current assets	3,906		3,906					7,338
Investments in Subsidiaries	17,021		17,021					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	6,109		6,109					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	50,219		50,219					50,738
Current Liabilities
Accounts Payable, Current	0		0					0
Accrued expenses and other current liabilities	346		346					230
Current portion of long-term debt, financing and capital lease obligations	2,569		2,569					1,373
Due to Affiliate, Current	0		0					0
Total current liabilities	2,915		2,915					1,603
Long-term debt, financing and capital lease obligations	9,085		9,085					10,660
Operating Lease, Liability, Noncurrent	0		0
Note due to consolidated affiliate	11,902		11,902					11,883
Deferred tax liabilities	0		0					0
Other liabilities	846		846					807
Due to affiliate	0		0					0
Total liabilities	24,748		24,748					24,953
Commitments and contingencies
Total stockholders' equity	25,471		25,471					25,785
Stockholders' Equity Attributable to Noncontrolling Interest	0		0					0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	25,471		25,471					25,785
Liabilities and Equity	50,219		50,219					50,738
Depreciation, equipment rentals	0	0	0	0
Non-Guarantor Subsidiaries [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Operating Lease, Liability, Current	1,860		1,860
Depreciation, network and other	1,071	1,088	3,256	3,132
Other Additional Capital	31	1,100	31	1,100
Current Assets
Cash and Cash Equivalents	247	485	247	485				377			$ 437
Short-term Investments	0		0					0
Accounts and notes receivable, net	3,873		3,873					3,554
Due from Affiliate, Current	0		0					0
Device and accessory inventory	1,117		1,117					999
Prepaid expenses and other current assets	1,209		1,209					1,280
Total current assets	6,446		6,446					6,210
Investments in Subsidiaries	0		0					0
Property, plant and equipment, net	20,827		20,827					21,201
Costs to acquire a customer contract	1,808		1,808					1,559
Operating Lease, Right-of-Use Asset	6,713		6,713
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	41,492		41,492					41,465
Property, plant and equipment	918		918					1,769
Other assets	1,051		1,051					1,066
Total assets	83,853		83,853					77,868
Current Liabilities
Accounts Payable, Current	3,396		3,396					3,961
Accrued expenses and other current liabilities	3,456		3,456					3,599
Current portion of long-term debt, financing and capital lease obligations	1,311		1,311					3,184
Due to Affiliate, Current	424		424					424
Total current liabilities	10,447		10,447					11,168
Long-term debt, financing and capital lease obligations	12,520		12,520					12,823
Operating Lease, Liability, Noncurrent	5,423		5,423
Note due to consolidated affiliate	23,143		23,143					23,567
Deferred tax liabilities	7,038		7,038					7,556
Other liabilities	1,862		1,862					2,630
Due to affiliate	6,399		6,399					2,706
Total liabilities	66,832		66,832					60,450
Commitments and contingencies
Total stockholders' equity	17,021		17,021					17,363
Stockholders' Equity Attributable to Noncontrolling Interest	0		0					55
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	17,021		17,021					17,418
Liabilities and Equity	83,853		83,853					$ 77,868
Depreciation, equipment rentals	$ 1,011	$ 1,137	$ 3,096	$ 3,454