CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - 9 months ended Dec. 31, 2017 - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interest [Member]
Balance (in shares) at Mar. 31, 2017		3,989
Beginning Balance at Mar. 31, 2017	$ 18,808	$ 40	$ 27,756	$ (8,584)	$ (404)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	7,314			7,320		$ (6)
Other Comprehensive Income (Loss), Net of Tax	38				38
Stock Issued During Period, Shares, New Issues		13
Stock Issued During Period, Value, New Issues	12		12
Share-based compensation expense	137		137
Capital contribution by SoftBank	5		5
Other, net	(57)		(57)
(Decrease) increase attributable to noncontrolling interests	48		(28)			76
Balance (in shares) at Dec. 31, 2017		4,002
Ending Balance at Dec. 31, 2017	$ 26,305	$ 40	$ 27,825	$ (1,264)	$ (366)	$ 70