Accounting for Share-Based Compensation 2 (Details) $ in Millions	9 Months Ended
	Dec. 31, 2016 USD ($)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 134
Weighted average period expected to be recognized (in years)	2 years 1 month 6 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
Restricted Stock Units
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 20
Weighted average period expected to be recognized (in years)	2 years
Restricted Stock Awards
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 76
Weighted average period expected to be recognized (in years)	1 year 10 months 24 days
Performance Share Units
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 33
Weighted average period expected to be recognized (in years)	2 years 6 months