CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Paid-in Capital [Member]	Treasury Shares [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive (Loss) Income [Member]
Balance (in shares) at Mar. 31, 2014		3,941		0
Balance at Mar. 31, 2014	$ 25,312	$ 39	$ 27,354	$ 0	$ (2,038)	$ (43)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(3,345)				(3,345)
Other comprehensive (loss) income	(365)					(365)
Issuance of common stock, net (in shares)		26
Issuance of common stock, net	35	$ 1	41
Issuance (repurchase) of common stock, net (in shares)				(1)
Issuance (repurchase) of common stock, net				$ (7)
Share-based compensation expense	71		71
Capital contribution by SoftBank			2
Balance (in shares) at Mar. 31, 2015		3,967		1
Balance at Mar. 31, 2015	21,710	$ 40	27,468	$ (7)	(5,383)	(408)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(1,995)				(1,995)
Other comprehensive (loss) income	(31)					(31)
Issuance of common stock, net (in shares)		7
Issuance of common stock, net	10		6
Issuance (repurchase) of common stock, net				$ 4
Share-based compensation expense	71		71
Capital contribution by SoftBank			14
Other, net			4
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]
Common stock, shares, issued	3,975
Net (loss) income	$ (1,206)				(1,206)
Other comprehensive (loss) income	35					35
Issuance of common stock, net (in shares)		15
Issuance of common stock, net	50		47
Issuance (repurchase) of common stock, net (in shares)				(1)
Issuance (repurchase) of common stock, net				$ 3
Share-based compensation expense	91		91
Capital contribution by SoftBank			6
Other, net			49
Balance (in shares) at Mar. 31, 2017		3,989		0
Balance at Mar. 31, 2017	$ 18,808	$ 40	$ 27,756	$ 0	$ (8,584)	$ (404)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, shares, issued	3,975