Goodwill (Details) - USD ($)	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Changes in the carrying amount of goodwill by segment [Roll Forward]
Goodwill, gross			$ 10,368,000,000
Accumulated impairment losses			(2,762,000,000)
Balance as of March 31, 2019, net			7,606,000,000
Acquisitions			1,202,000,000
Foreign currency translation			(137,000,000)
Impairment losses	$ (2,887,000,000)	$ 0	(2,887,000,000)	$ 0
Goodwill, gross	11,433,000,000		11,433,000,000
Accumulated impairment losses	(5,649,000,000)		(5,649,000,000)
Balance as of September 30, 2019, net	5,784,000,000		5,784,000,000
GBS
Changes in the carrying amount of goodwill by segment [Roll Forward]
Goodwill, gross			5,300,000,000
Accumulated impairment losses			(701,000,000)
Balance as of March 31, 2019, net			4,599,000,000
Acquisitions			1,202,000,000
Foreign currency translation			(72,000,000)
Impairment losses			(2,625,000,000)
Goodwill, gross	6,430,000,000		6,430,000,000
Accumulated impairment losses	(3,326,000,000)		(3,326,000,000)
Balance as of September 30, 2019, net	3,104,000,000		3,104,000,000
GIS
Changes in the carrying amount of goodwill by segment [Roll Forward]
Goodwill, gross			5,068,000,000
Accumulated impairment losses			(2,061,000,000)
Balance as of March 31, 2019, net			3,007,000,000
Acquisitions			0
Foreign currency translation			(65,000,000)
Impairment losses			(262,000,000)
Goodwill, gross	5,003,000,000		5,003,000,000
Accumulated impairment losses	(2,323,000,000)		(2,323,000,000)
Balance as of September 30, 2019, net	$ 2,680,000,000		$ 2,680,000,000