Segment Information 1 (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Company's segment information
Revenue	$ 1,152		$ 1,200		$ 2,297		$ 2,363
Expenses	746		822		1,452		1,568
Segment profit	337		333		718		675
Segment operating margin	35.00%		32.00%		37.00%		34.00%
Depreciation and amortization					212		195
Reconciliation of segment profit to income from continuing operations before income taxes
Segment profit	337		333		718		675
Depreciation and amortization					212		195
Share-based compensation expense	21		16		44		41
Other (gains) expenses, net	8	[1]	(12)	[1]	2	[1]	(4)	[1]
Interest expense, net	10		6		21		15
Income from continuing operations before income taxes	327		327		697		660
Mainframe Solutions [Member]
Company's segment information
Revenue	619		655		1,247		1,301
Expenses	247		308		507		584
Segment profit	372		347		740		717
Segment operating margin	60.00%		53.00%		59.00%		55.00%
Depreciation and amortization	27		25		53		49
Reconciliation of segment profit to income from continuing operations before income taxes
Segment profit	372		347		740		717
Depreciation and amortization	27		25		53		49
Enterprise Solutions [Member]
Company's segment information
Revenue	438		449		864		876
Expenses	410		422		769		804
Segment profit	28		27		95		72
Segment operating margin	6.00%		6.00%		11.00%		8.00%
Depreciation and amortization	40		32		78		63
Reconciliation of segment profit to income from continuing operations before income taxes
Segment profit	28		27		95		72
Depreciation and amortization	40		32		78		63
Services [Member]
Company's segment information
Revenue	95		96		186		186
Expenses	89		92		176		180
Segment profit	6		4		10		6
Segment operating margin	6.00%		4.00%		5.00%		3.00%
Depreciation and amortization	0		0		0		0
Reconciliation of segment profit to income from continuing operations before income taxes
Segment profit	6		4		10		6
Depreciation and amortization	0		0		0		0
Reportable Segments Only [Member]
Company's segment information
Segment profit	406		378		845		795
Depreciation and amortization	67		57		131		112
Reconciliation of segment profit to income from continuing operations before income taxes
Segment profit	406		378		845		795
Depreciation and amortization	67		57		131		112
Depreciation and Amortization of Developed Software [Member] | Purchased Software Products [Member]
Company's segment information
Depreciation and amortization	27		26		54		49
Reconciliation of segment profit to income from continuing operations before income taxes
Depreciation and amortization	27		26		54		49
Depreciation and Amortization of Developed Software [Member] | Other Intangible Assets [Member]
Company's segment information
Depreciation and amortization	13		15		27		34
Reconciliation of segment profit to income from continuing operations before income taxes
Depreciation and amortization	$ 13		$ 15		$ 27		$ 34

[1] Other (gains) expenses, net consists of other unallocated costs including foreign exchange derivative (gains) losses, and other miscellaneous costs.