Long-Lived Assets 5 (Details) - USD ($) $ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Goodwill activity by segment
Balance at beginning of year		$ 6,857	$ 6,086
Acquisitions			771
Acquisitions	[1]	(105)
Foreign currency translation adjustment		52
Balance at end of year		6,804	6,857
Mainframe Solutions
Goodwill activity by segment
Balance at beginning of year		4,178	4,178
Acquisitions			0
Acquisitions		0
Foreign currency translation adjustment		0
Balance at end of year		4,178	4,178
Enterprise Solutions
Goodwill activity by segment
Balance at beginning of year		2,598	1,827
Acquisitions			771
Acquisitions	[1]	(105)
Foreign currency translation adjustment		52
Balance at end of year		2,545	2,598
Services
Goodwill activity by segment
Balance at beginning of year		81	81
Acquisitions			0
Acquisitions		0
Foreign currency translation adjustment		0
Balance at end of year		$ 81	$ 81

[1] Acquisitions amount relates to purchase price allocation adjustments that occurred during fiscal year 2018.