Accounting for Share-Based Compensation 2 (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Sep. 30, 2012
Unrecognized share based compensation cost
Unrecognized compensation costs	$ 137
Weighted average period expected to be recognized	2 years 3 months 18 days
Stock Option Awards [Member]
Unrecognized share based compensation cost
Unrecognized compensation costs	7
Weighted average period expected to be recognized	2 years 3 months 18 days
Restricted Stock Units [Member]
Unrecognized share based compensation cost
Unrecognized compensation costs	19
Weighted average period expected to be recognized	2 years 1 month 6 days
Restricted Stock Awards [Member]
Unrecognized share based compensation cost
Unrecognized compensation costs	81
Weighted average period expected to be recognized	2 years 1 month 6 days
Performance Share Units [Member]
Unrecognized share based compensation cost
Unrecognized compensation costs	$ 30
Weighted average period expected to be recognized	2 years 9 months 18 days