Segments (Statement of Operations Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Impairments	$ (210)	$ 0
Segment Reporting Information, Total Net Operating Revenues	(8,142)	(8,125)
Revenues	8,142	8,125
Segment Operating Expenses	5,100	4,845
Segment Reporting Information Operating Income or Loss	3,042	3,280
Depreciation, network and other	1,120	1,023
Depreciation, equipment rentals	1,029	1,136
Amortization	118	171
Merger costs	83	93
Other Operating Expenses Net	(237)	(42)
Selling, general and administrative	1,907	1,867
Operating Income	455	815
Interest Expense	619	637
Other income, net	28	42
Loss (income) before income taxes	(136)	220
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease	2,705	2,949
Severance and exit costs	(27)
Wireless [Member]
Segment Reporting Information [Line Items]
Revenues	7,901	7,845
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease	2,543	2,836
Gain (Loss) on Contract Termination		(34)
Wireless [Member] | Wireless Excluding Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	(7,901)	(7,845)
Segment Operating Expenses	(4,864)	4,527
Segment Reporting Information Operating Income or Loss	3,037	3,318
Wireline [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	(236)	(276)
Revenues	307	338
Segment Operating Expenses	(307)	380
Segment Reporting Information Operating Income or Loss	0	(42)
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease	28	51
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	(5)	(4)
Revenues	(66)	(58)
Segment Operating Expenses	71	(62)
Segment Reporting Information Operating Income or Loss	5	4
Payments to Acquire Property, Plant and Equipment Inclusive of Equipment on Lease	134	62
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	0	0
Intersegment Eliminations [Member] | Wireless [Member] | Wireless Excluding Hurricane and Other [Member]
Segment Reporting Information [Line Items]
Revenues	0	0
Intersegment Eliminations [Member] | Wireline [Member]
Segment Reporting Information [Line Items]
Revenues	71	(62)
Intersegment Eliminations [Member] | Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues	$ (71)	(62)
Lease and severance [Member]
Segment Reporting Information [Line Items]
Severance and exit costs		$ (8)