(Fair Value Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Mar. 31, 2017
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Total assets at fair value		$ 3,299	$ 2,778
Total liabilities at fair value		174	17
Quoted Prices In Active Markets For Identical Financial Instruments (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Total assets at fair value		1,318	1,106
Total liabilities at fair value		11	9
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Total assets at fair value		1,981	1,672
Total liabilities at fair value		41	8
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Total assets at fair value		0	0
Total liabilities at fair value		122	0
Short-term investments | Quoted Prices In Active Markets For Identical Financial Instruments (Level 1) | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities		446
Short-term investments | Significant Other Observable Inputs (Level 2) | Foreign Government Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities			113
Short-term investments | Significant Other Observable Inputs (Level 2) | Asset-backed Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Asset-backed securities		134	135
Short-term investments | Significant Other Observable Inputs (Level 2) | Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities		22
Short-Term Investments And Cash Equivalents | Quoted Prices In Active Markets For Identical Financial Instruments (Level 1) | U.S. Treasury securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities			460
Short-Term Investments And Cash Equivalents | Significant Other Observable Inputs (Level 2) | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities		1,258	963
Short-Term Investments And Cash Equivalents | Significant Other Observable Inputs (Level 2) | U.S. agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities		118	172
Short-Term Investments And Cash Equivalents | Significant Other Observable Inputs (Level 2) | Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities		341	270
Short-Term Investments And Cash Equivalents | Significant Other Observable Inputs (Level 2) | Foreign Government Debt Securities [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Available-for-sale of securities		100
Cash Equivalents | Quoted Prices In Active Markets For Identical Financial Instruments (Level 1) | Bank Time Deposits [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Cash equivalents		299	233
Cash Equivalents | Quoted Prices In Active Markets For Identical Financial Instruments (Level 1) | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Cash equivalents		563	405
Other Current Assets and Other Assets [Domain] | Significant Other Observable Inputs (Level 2) | Foreign currency derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Foreign currency derivatives, assets		8	19
Other assets | Quoted Prices In Active Markets For Identical Financial Instruments (Level 1) | Deferred compensation plan assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Deferred compensation plan assets	[1]	10	8
Accrued and Other Current Liabilities and Other Liabilities | Significant Other Observable Inputs (Level 2) | Foreign currency derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Foreign currency derivatives, liabilities		41	8
Other liabilities | Quoted Prices In Active Markets For Identical Financial Instruments (Level 1) | Deferred Compensation Plan Liabilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Fair value, Deferred compensation plan assets	[1]	11	9
Other liabilities | Fair Value, Inputs, Level 3 [Member] | Contingent consideration
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Accrued Liabilities, Fair Value Disclosure		$ 122	$ 0

[1] The Deferred Compensation Plan assets consist of various mutual funds. See Note 13 in our Annual Report on Form 10-K for the fiscal year ended March 31, 2017, for additional information regarding our Deferred Compensation Plan.