Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	$ 1,000		$ 1,000
Loss on disposition of property, plant, and equipment			692	$ 642
Impairment of real estate			207
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Increase (decrease) in inventories			888	645
Accrued capital expenditures	175	$ 264	175	264
Network Equipment
Property, Plant and Equipment [Line Items]
Loss on disposition of property, plant, and equipment			(26)
Other, Net [Member]
Property, Plant and Equipment [Line Items]
Loss on disposition of property, plant, and equipment	(227)	(299)	(692)	(642)
Write-off leased devices [Member]
Property, Plant and Equipment [Line Items]
Loss on disposition of property, plant, and equipment	$ (201)	$ (182)	$ (666)	$ (457)