Share-Based Compensation (Components Of Share-Based Compensation Expense And Related Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Mar. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 154		$ 137		$ 114
Tax benefit for share-based compensation expense	(55)	[1]	(48)	[1]	(41)	[1]
Share-based compensation expense, net of tax	99		89		73
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	97	[2]	79	[2]	47	[2]
PeRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	24	[3]	27	[3]	39	[3]
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	23		22		19
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 10		$ 9		$ 9

[1] Income tax expense is computed using the tax rates of applicable tax jurisdictions. Additionally, a portion of pre-tax compensation expense is not tax-deductible.

[2] This expense was primarily the result of PeRSUs awarded in prior years, which converted to RSUs due to the attainment of goals during the applicable years' performance period.

[3] Represents estimated compensation expense for PeRSUs that are conditional upon attaining performance objectives during the current year's performance period.