Accounting for Share-Based Compensation 2 (Details) $ in Millions	9 Months Ended
	Dec. 31, 2017 USD ($)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 141
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)	1 year 10 months 24 days
Restricted Stock Units (RSUs)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 21
Weighted average period expected to be recognized (in years)	1 year 10 months 24 days
Restricted Stock Awards (RSAs)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 78
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	$ 37
Weighted average period expected to be recognized (in years)	2 years 4 months 24 days