Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Increase (Decrease) in Accounts Payable			$ 310	$ 854
Sale Leaseback Transaction, Net Book Value	$ 502		502		$ 1,200	$ 1,300
Depreciation	1,710	$ 1,412	3,390	2,653
Loss on Disposition of Property Plant Equipment	111	85	$ 231	85
Document Period End Date			Sep. 30, 2016
Leased devices [Member]
Property, Plant and Equipment [Line Items]
Increase (Decrease) in Accounts Payable			$ 96	206
Increase (Decrease) in Inventories			1,200	1,600
Depreciation	$ 724	420	$ 1,400	$ 696
Wireline [Member]
Property, Plant and Equipment [Line Items]
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss		$ 233