Description Of Business And Basis Of Presentation Accounting Standard Cash Flow Reclassification (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash paid to taxing authorities for shares withheld from employees	$ 112	$ 112
Increase to net cash provided by Operating Activities and net cash used in Financing Activities	152	165
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		53
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	112	$ 112
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	$ 40