Description Of Business And Basis Of Presentation Description of Business and Basis of Presentation (Impact of Recently Adopted Accounting Standards) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Accounting Standards Update 2016-09 [Member]
Change in Accounting Estimate [Line Items]
Cumulative Effect on Retained Earnings, Net of Tax		$ 8
Increase to net cash provided by Operating Activities [Member]
Change in Accounting Estimate [Line Items]
Excess Tax Benefit from Share-based Compensation, Operating Activities			$ 37
Provision for income taxes [Member] | Increase to net cash provided by Operating Activities [Member]
Change in Accounting Estimate [Line Items]
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 3	$ 42