Income Taxes (Gross Unrecognized Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Income Taxes [Abstract]
Unrecognized tax benefits at beginning of period	$ 635	$ 619	$ 526
Additions based on tax positions related to prior years	11	32	50
Reductions based on tax positions related to prior years	(72)	(60)	(12)
Additions based on tax positions related to current year	37	50	72
Reductions based on settlements	(1)	(6)	(16)
Reductions based on the lapse of the applicable statutes of limitations	(15)	0	(1)
Unrecognized tax benefits at end of period	$ 595	$ 635	$ 619