Share-Based Compensation (Data Related to RSU Activity) (Details) (Restricted Stock Units (RSUs) [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 184	$ 66	$ 44
Total compensation cost, net of estimated forfeitures, related to nonvested RSU awards not yet recognized, pre-tax	$ 115	$ 128	$ 143
Weighted-average period in years over which RSU cost is expected to be recognized	2 years	2 years	3 years