Description Of Business And Summary Of Significant Accounting Policies (Advertising Costs) (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Operating Expenses [Abstract]
Vendor reimbursements of advertising costs	$ 45	$ 53	$ 51
Advertising expense, net of vendor reimbursements	$ 261	$ 281	$ 240

Total amount received by an entity from a vendor under a cooperative advertising arrangement that has been offset against advertising expense.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 50
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=68069731&loc=d3e63872-111659

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 705
-SubTopic 20
-Section 25
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=68067574&loc=SL51760044-203187

Name:	us-gaap_CooperativeAdvertisingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration