Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Property, Plant and Equipment [Line Items]
Increase (Decrease) in Accounts Payable			$ 325	$ 763
Sale Leaseback Transaction, Net Book Value	$ 447	$ 1,300	447	1,300	$ 1,200
Depreciation	1,837	1,549	5,227	4,202
Loss on Disposition of Property Plant Equipment	137		$ 368	228
Document Period End Date			Dec. 31, 2016
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Increase (Decrease) in Accounts Payable			$ 166	306
Increase (Decrease) in Inventories			2,300	2,600
Depreciation	837	535	2,200	1,231
Wireline [Member]
Property, Plant and Equipment [Line Items]
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss		233
Write-off leased devices [Member]
Property, Plant and Equipment [Line Items]
Loss on Disposition of Property Plant Equipment	$ (109)	$ 78	$ (340)	$ 163