Share-Based Compensation (Components of Share-Based Compensation Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 174		$ 160		$ 167
Tax benefit for share-based compensation expense	(61)	[1]	(55)	[1]	(59)	[1]
Share-based compensation expense, net of tax	113		105		108
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	137	[2]	126	[2]	132	[2]
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	24		22		24
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 13		$ 12		$ 11

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

[2] RSUs, PeRSUs and TSRUs. Our TSRUs were awarded beginning in 2015.