Segments (Statement of Operations Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Document Period End Date			Dec. 31, 2019
Asset impairment - campus			$ 231
Impairments	$ (19)		(231)	$ 0
Segment Reporting Information, Total Net Operating Revenues	(8,080)	$ (8,601)	(24,017)	(25,156)
Revenues	8,080	8,601	24,017	25,159
Segment Operating Expenses	5,532	5,500	15,873	15,519
Segment Reporting Information Operating Income or Loss	2,548	3,101	8,144	9,637
Depreciation, network and other	1,071	1,088	3,256	3,132
Depreciation, equipment rentals	1,011	1,137	3,096	3,454
Amortization	474	145	698	475
Hurricane-related charges				(32)
Merger costs	78	67	230	216
Other Operating Expenses Net	152	(185)	(106)	(320)
Selling, general and administrative	2,045	2,003	5,888	5,731
Operating Income	66	479	758	2,072
Interest Expense	589	664	1,802	1,934
Other income, net	(6)	32	36	153
Loss (income) before income taxes	(529)	(153)	(1,008)	291
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease			8,809	9,553
Severance and exit costs	(20)		(66)
Litigation Settlement, Expense			270	(50)
Loss on disposition of property, plant, and equipment			692	642
Gain Loss from asset dispositions and exchanges			4	12
Partial pension plan settlement			(57)
Wireless [Member]
Segment Reporting Information [Line Items]
Revenues	7,859	8,351	23,327	24,362
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease			8,360	9,101
Gain (Loss) on Contract Termination				(34)
Wireless [Member] | Wireless Including Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues				(24,365)
Segment Operating Expenses				(14,650)
Segment Reporting Information Operating Income or Loss				9,715
Wireless [Member] | Wireless Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		(3)		3
Segment Operating Expenses				(7)
Segment Reporting Information Operating Income or Loss				(10)
Wireless [Member] | Wireless Excluding Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	(7,859)	(8,351)	(23,327)	(24,362)
Segment Operating Expenses	(5,324)	5,240	(15,193)	14,657
Segment Reporting Information Operating Income or Loss	2,535	3,111	8,134	9,705
Wireline [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	(222)	(245)	(685)	(781)
Revenues	296	316	903	982
Segment Operating Expenses	(284)	332	(896)	1,060
Segment Reporting Information Operating Income or Loss	12	(16)	7	(78)
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease			92	170
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	1	(5)	(5)	(13)
Revenues	(75)	(66)	(213)	(188)
Segment Operating Expenses	76	(72)	216	(198)
Segment Reporting Information Operating Income or Loss	1	6	3	10
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease			357	282
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations [Member] | Wireless [Member] | Wireless Including Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Revenues				0
Intersegment Eliminations [Member] | Wireless [Member] | Wireless Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Revenues				0
Intersegment Eliminations [Member] | Wireless [Member] | Wireless Excluding Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Intersegment Eliminations [Member] | Wireline [Member]
Segment Reporting Information [Line Items]
Revenues	74	(71)	218	201
Intersegment Eliminations [Member] | Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	(74)	(71)	(218)	(201)
Other, Net [Member]
Segment Reporting Information [Line Items]
Loss on disposition of property, plant, and equipment	$ (227)	(299)	(692)	(642)
Cost of Sales [Member] | Other, Net [Member]
Segment Reporting Information [Line Items]
Other Operating Expenses Net		(6)
Other, Net [Member] | Other, Net [Member]
Segment Reporting Information [Line Items]
Other Operating Expenses Net		(22)
Selling, general and administrative		1
Network equipment, site costs and related software [Member]
Segment Reporting Information [Line Items]
Loss on disposition of property, plant, and equipment		(117)	$ (26)	(185)
Lease and severance [Member]
Segment Reporting Information [Line Items]
Severance and exit costs		$ 30		$ 63