Accounting for Share-Based Compensation 2 (Details) $ in Millions	6 Months Ended
	Sep. 30, 2015 USD ($)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 139
Weighted average period expected to be recognized (in years)	2 years 3 months 18 days
Stock Option Awards
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 7
Weighted average period expected to be recognized (in years)	2 years
Restricted Stock Units
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 24
Weighted average period expected to be recognized (in years)	2 years 2 months 12 days
Restricted Stock Awards
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 80
Weighted average period expected to be recognized (in years)	2 years 2 months 12 days
Performance Share Units
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 28
Weighted average period expected to be recognized (in years)	2 years 7 months 6 days