CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - 6 months ended Sep. 30, 2017 - 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, 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]
Net loss	158				158
Other Comprehensive Income (Loss), Net of Tax	12					12
Stock Issued During Period, Shares, New Issues		11
Stock Issued During Period, Value, New Issues	1		10
Share-based compensation expense	87		87
Capital contribution by SoftBank	5		5
Other, net	(51)		(51)
Balance (in shares) at Sep. 30, 2017		4,000		1
Balance at Sep. 30, 2017	$ 19,020	$ 40	$ 27,807	$ (9)	$ (8,426)	$ (392)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Treasury Stock Reissued				1
Stock Issued During Period, Value, Treasury Stock Reissued				$ (9)