Description Of Business And Summary Of Significant Accounting Policies Accounting Standard Cash Flow Reclassification (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit from stock-based compensation	$ 65	$ 86	$ 22
Increase to net cash provided by Operating Activities and net cash used in Financing Activities	195	242	105
Increase to net cash provided by Operating Activities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excess tax benefit from stock-based compensation	65	86	22
Increase to net cash provided by Operating Activities [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash Paid for Withholding Taxes	$ 130	$ 156	$ 83