Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended														12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2013 Stock Option [Member]	Mar. 31, 2012 Stock Option [Member]	Mar. 31, 2011 Stock Option [Member]	Mar. 31, 2013 Restricted Stock Units (RSUs) [Member]	Mar. 31, 2012 Restricted Stock Units (RSUs) [Member]	Mar. 31, 2011 Restricted Stock Units (RSUs) [Member]	Mar. 31, 2013 Restricted Stock Units (RSUs) [Member] Minimum [Member]	Mar. 31, 2013 Restricted Stock Units (RSUs) [Member] Maximum [Member]	Mar. 31, 2013 Performance Shares [Member]	May 31, 2012 Performance Shares [Member]	Mar. 31, 2013 Employee Stock [Member]	Mar. 31, 2012 Employee Stock [Member]	Mar. 31, 2011 Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Authorized	42,500,000													1,000,000	16,000,000
Number of Shares Available for Future Grant	5,800,000														1,000,000
Contractual Term of Stock Plan, Years	5 years		5 years	5 years	7 years
Vesting period, years					4 years						3 years	4 years	4 years
Vested and Expected to Vest, Shares	6,000,000	[1]						140,000
Total compensation cost, net of estimated forfeitures, related to unvested share-based awards not yet recognized, pre-tax					$ 37	$ 40	$ 41	$ 128	$ 143	$ 131			$ 82
Weighted-average period in years over which RSU cost is expected to be recognized					1 year	1 year	1 year	2 years	3 years	2 years			3 years
Period to purchase a shares through payroll deductions, months															3 months
Percentage of price to purchase shares through payroll deductions															85.00%
Percentage of deduction to purchase shares through payroll deductions															15.00%
Shares issued under ESPP															1,000,000	1,000,000	1,000,000

[1] The number of options expected to vest takes into account an estimate of expected forfeitures.