Accounting Policies - Fiscal Year and Inventories (Details)	12 Months Ended
Apr. 29, 2017	Apr. 30, 2016	Apr. 25, 2015
Accounting Policies
Length of fiscal year	364 days	371 days	364 days
Inventories
Inventory cost determined using LIFO basis (as a percent)	63.00%	70.00%

Duration of a fiscal period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but not limited to, weeks in a year or quarter.

No definition available.

Name:	us-gaap_FiscalPeriodDuration
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration