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Summary Of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended
Apr. 05, 2015
Mar. 30, 2014
Accounting Policies [Abstract]    
Length of fiscal quarters, weeks 0 years 0 months 91 days  
Net increase in operating earnings from the quarterly impact of revisions in contract $ 63gd_NetIncreaseDecreaseInOperatingEarningsFromQuarterlyImpactOfRevisionsInContractEstimates $ 38gd_NetIncreaseDecreaseInOperatingEarningsFromQuarterlyImpactOfRevisionsInContractEstimates
Net increase in operating earnings per share from the quarterly impact of revisions in contract $ 0.12gd_NetIncreaseDecreaseInOperatingEarningsPerShareFromQuarterlyImpactOfRevisionsInContractEstimates $ 0.07gd_NetIncreaseDecreaseInOperatingEarningsPerShareFromQuarterlyImpactOfRevisionsInContractEstimates