New Accounting Pronouncements - Cumulative Effects of Accounting Standards Update on Statement of Comprehensive Income and Balance Sheet (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service revenue	$ 8,142	$ 8,125
Revenue, equipment sales, net	1,220	1,173
Revenue, equipment rentals, net	1,359	1,212
Revenues	8,142	8,125
Cost of equipment sales	1,341	1,270
Cost of equipment rentals	225	124
Selling, general and administrative	1,907	1,867
Severance and exit costs	(27)
Depreciation, network and other	1,120	1,023
Depreciation, equipment rentals	1,029	1,136
Amortization	118	171
Other, net	237	42
Total costs and expenses	7,687	7,310
Operating Income	455	815
Total other expense	(591)	(595)
Loss (income) before income taxes	(136)	220
Income tax benefit	22	(47)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(114)	173
Net Income (Loss) Attributable to Noncontrolling Interest	3	3
Net Income (Loss) Attributable to Parent	$ (111)	$ 176
Basic net (loss) income per common share	$ (0.03)	$ 0.04
Diluted net (loss) income per common share	$ (0.03)	$ 0.04
Basic weighted average common shares outstanding	4,087	4,010
Diluted weighted average common shares outstanding	4,087	4,061
Services [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Service revenue	$ 5,563	$ 5,740