Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	$ 1,100	$ 1,200	$ 1,100	$ 1,200
Loss on Disposition of Property Plant Equipment			465	343
Impairment of Real Estate			207
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Accrued capital expenditures	127	207	127	207
Increase (Decrease) in Inventories			539	399
Network equipment, site costs and related software [Member]
Property, Plant and Equipment [Line Items]
Loss on Disposition of Property Plant Equipment				(68)
Other, Net [Member]
Property, Plant and Equipment [Line Items]
Loss on Disposition of Property Plant Equipment	$ (240)	(219)	$ (465)	(343)
Write-off leased devices [Member]
Property, Plant and Equipment [Line Items]
Loss on Disposition of Property Plant Equipment		$ (151)		$ (275)