CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - 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]	Noncontrolling Interest [Member]
Total stockholders' equity				$ 0
Net Income (Loss) Attributable to Parent					$ 206
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)	206
Other Comprehensive Income, Other, Net of Tax						(4)
Stock Issued During Period, Shares, New Issues		7
Stock Issued During Period, Value, New Issues	9		9
Share-based compensation expense	40		40
Capital contribution by SoftBank	2		2
Other, net	(46)		(46)
Balance (in shares) at Jun. 30, 2017		3,996		0
Ending Balance at Jun. 30, 2017	19,015	$ 40	27,761		(8,378)	(408)
Net Income (Loss) Attributable to Parent	158
Balance (in shares) at Mar. 31, 2017		3,989
Beginning Balance at Mar. 31, 2017	18,808	$ 40	27,756		(8,584)	(404)
Balance (in shares) at Sep. 30, 2017		4,000		1
Ending Balance at Sep. 30, 2017	19,020	$ 40	27,807		(8,426)	(392)
Total stockholders' equity				$ 0
Net Income (Loss) Attributable to Parent	(48)				(48)
Balance (in shares) at Jun. 30, 2017		3,996		0
Beginning Balance at Jun. 30, 2017	19,015	$ 40	27,761		(8,378)	(408)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(48)
Other Comprehensive Income, Other, Net of Tax						16
Stock Issued During Period, Shares, New Issues		4
Stock Issued During Period, Value, New Issues	(8)		1
Stock Issued During Period, Shares, Treasury Stock Reissued				1
Stock Issued During Period, Value, Treasury Stock Reissued				$ (9)
Share-based compensation expense	47		47
Capital contribution by SoftBank	3		3
Other, net	(5)		(5)
Balance (in shares) at Sep. 30, 2017		4,000		1
Ending Balance at Sep. 30, 2017	19,020	$ 40	27,807		(8,426)	(392)
Total stockholders' equity				$ (9)
Total stockholders' equity	26,356			$ 0
Net Income (Loss) Attributable to Parent					176
Balance (in shares) at Mar. 31, 2018		4,005
Beginning Balance at Mar. 31, 2018	26,419	$ 40	27,884		(1,255)	(313)	$ 63
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	173						(3)
Other Comprehensive Income, Other, Net of Tax						4
Stock Issued During Period, Shares, New Issues		8
Stock Issued During Period, Value, New Issues	(2)		2
Stock Issued During Period, Shares, Treasury Stock Reissued				1
Stock Issued During Period, Value, Treasury Stock Reissued				$ (4)
Share-based compensation expense	40		40
Capital contribution by SoftBank	1		1
Cumulative effect of accounting changes	1,307				1,315	(8)
Other, net	3		3
Increase (decrease) attributable to noncontrolling interests	0		8				(8)
Balance (in shares) at Jun. 30, 2018		4,013		1
Ending Balance at Jun. 30, 2018	27,945	$ 40	27,938		236	(317)	52
Net Income (Loss) Attributable to Parent	372
Balance (in shares) at Mar. 31, 2018		4,005
Beginning Balance at Mar. 31, 2018	26,419	$ 40	27,884		(1,255)	(313)	63
Balance (in shares) at Sep. 30, 2018		4,079		2
Ending Balance at Sep. 30, 2018	28,464	$ 41	28,251		432	(308)	63
Total stockholders' equity				$ (4)
Net Income (Loss) Attributable to Parent	196				196
Balance (in shares) at Jun. 30, 2018		4,013		1
Beginning Balance at Jun. 30, 2018	27,945	$ 40	27,938		236	(317)	52
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	207						11
Other Comprehensive Income, Other, Net of Tax						9
Stock Issued During Period, Shares, New Issues		66
Stock Issued During Period, Value, New Issues	278	$ 1	288
Stock Issued During Period, Shares, Treasury Stock Reissued				1
Stock Issued During Period, Value, Treasury Stock Reissued				$ (11)
Share-based compensation expense	27		27
Capital contribution by SoftBank	1		1
Cumulative effect of accounting changes						0
Other, net	(3)		(3)
Balance (in shares) at Sep. 30, 2018		4,079		2
Ending Balance at Sep. 30, 2018	28,464	$ 41	$ 28,251		$ 432	$ (308)	$ 63
Total stockholders' equity	$ 28,401			$ (15)