CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - 9 months ended Dec. 31, 2016 - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Balance (in shares) at Mar. 31, 2016		3,974		1
Balance at Mar. 31, 2016	$ 19,783	$ 40	$ 27,563	$ (3)	$ (7,378)	$ (439)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(923)				(923)
Other Comprehensive Income (Loss), Net of Tax	2					2
Stock Issued During Period, Shares, New Issues		11
Stock Issued During Period, Value, New Issues	35		32
Stock Issued During Period, Shares, Treasury Stock Reissued				(1)
Stock Issued During Period, Value, Treasury Stock Reissued				$ 3
Share-based compensation expense	56		56
Capital contribution by SoftBank	6		6
Other, net	37		37
Balance (in shares) at Dec. 31, 2016		3,985		0
Balance at Dec. 31, 2016	$ 18,996	$ 40	$ 27,694	$ 0	$ (8,301)	$ (437)