Description Of Business And Summary Of Significant Accounting Policies (Advertising Costs) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Operating Expenses [Abstract]      
Vendor reimbursements of advertising costs $ 43 $ 66 $ 45
Advertising expense, net of vendor reimbursements $ 228 $ 217 $ 240