Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Financial Instruments [Line Items]
Cash and cash equivalents	$ 1,292	$ 1,293	$ 1,579	$ 1,273
Proceeds from sale of marketable equity securities	72	0	132
Contractual interest rate of 0.75% Convertible Senior Notes due 2016	0.75%	0.75%
The9 [Member]
Financial Instruments [Line Items]
Proceeds from sale of marketable equity securities			11
Realized gain (loss) on sale of investment			3
Total impairments of marketable securities			2
Ubisoft [Member]
Financial Instruments [Line Items]
Proceeds from sale of marketable equity securities			121
Realized gain (loss) on sale of investment			28
Neowiz [Member]
Financial Instruments [Line Items]
Proceeds from sale of marketable equity securities	72
Realized gain (loss) on sale of investment	$ 39
0.75% Convertible Senior Notes Due 2016 [Member]
Financial Instruments [Line Items]
Contractual interest rate of 0.75% Convertible Senior Notes due 2016		0.75%
Convertible Senior Notes, maturity date (year)		2016