Accounting for Share-Based Compensation 2 (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Sep. 30, 2013
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 131
Weighted average period expected to be recognized	2 years 3 months 18 days
Stock Option Awards [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	10
Weighted average period expected to be recognized	2 years 4 months 24 days
Restricted Stock Units [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	24
Weighted average period expected to be recognized	2 years 2 months 12 days
Restricted Stock Awards [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	75
Weighted average period expected to be recognized	2 years 1 month 6 days
Performance Share Units [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 22
Weighted average period expected to be recognized	2 years 9 months 18 days