Accounting for Share-Based Compensation 2 (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2013
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 148
Weighted average period expected to be recognized	2 years 6 months 0 days
Stock Option Awards [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	9
Weighted average period expected to be recognized	2 years 6 months 0 days
Restricted Stock Units [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	26
Weighted average period expected to be recognized	2 years 4 months 24 days
Restricted Stock Awards [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	89
Weighted average period expected to be recognized	2 years 3 months 18 days
Performance Share Units [Member]
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 24
Weighted average period expected to be recognized	3 years 0 months 0 days