Accounting for Share-Based Compensation 2 (Details) $ in Millions	6 Months Ended
	Sep. 30, 2016 USD ($)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 158
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	$ 5
Weighted average period expected to be recognized (in years)	2 years 2 months 12 days
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	$ 89
Weighted average period expected to be recognized (in years)	2 years 1 month 6 days
Performance Share Units
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 40
Weighted average period expected to be recognized (in years)	2 years 8 months 12 days