Description Of Business And Basis Of Presentation Accounting Standard Cash Flow Reclassification (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash paid to taxing authorities for shares withheld from employees		$ 105	$ 106
Increase to net cash provided by Operating Activities and net cash used in Financing Activities		147	143
Increase to net cash provided by Operating Activities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess Tax Benefit from Share-based Compensation, Operating Activities			37
Increase to net cash used in Financing Activities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash paid to taxing authorities for shares withheld from employees		105	$ 106
Provision for income taxes [Member] | Increase to net cash provided by Operating Activities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 3	$ 42