Accounting for Share-Based Compensation 2 (Details) $ in Millions	3 Months Ended
	Jun. 30, 2017 USD ($)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 193
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 2 months 12 days
Restricted Stock Units (RSUs)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 29
Weighted average period expected to be recognized (in years)	2 years 2 months 12 days
Restricted Stock Awards (RSAs)
Unrecognized share-based compensation costs
Unrecognized share-based compensation costs	$ 107
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	$ 50
Weighted average period expected to be recognized (in years)	2 years 8 months 12 days