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Debt - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Debt Outstanding [Line Items]    
Percentage of owned subsidiaries guaranteed 100.00%gd_PercentageOfOwnedSubsidiariesGuaranteedFixedRateNotes  
Multi-Year Facility, Expiring July 2016    
Debt Outstanding [Line Items]    
Expiration dates   2016-07
Multi Year Facility Expiring July 2018    
Debt Outstanding [Line Items]    
Expiration dates   2018-07
Commercial Paper    
Debt Outstanding [Line Items]    
Percentage of owned subsidiaries guaranteed 100.00%gd_PercentageOfOwnedSubsidiariesGuaranteedFixedRateNotes
/ us-gaap_LineOfCreditFacilityAxis
= us-gaap_CommercialPaperMember
 
Credit facilities 2,000,000,000us-gaap_LineOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= us-gaap_CommercialPaperMember
 
Remaining borrowing capacity 130,000,000us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= us-gaap_CommercialPaperMember
 
Commercial Paper | Multi-Year Facility, Expiring July 2016    
Debt Outstanding [Line Items]    
Credit facilities 1,000,000,000us-gaap_LineOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= us-gaap_CommercialPaperMember
/ us-gaap_LongtermDebtTypeAxis
= gd_MultiYearFacilityExpiringJulyTwoThousandSixteenMember
 
Commercial Paper | Multi Year Facility Expiring July 2018    
Debt Outstanding [Line Items]    
Credit facilities 1,000,000,000us-gaap_LineOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= us-gaap_CommercialPaperMember
/ us-gaap_LongtermDebtTypeAxis
= gd_MultiYearFacilityExpiringJuly2018Domain