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Summary Of Significant Accounting Policies - Research and Development Expenses (Details) (Company-sponsored R & D, including product development costs, USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Company-sponsored R & D, including product development costs
     
Research and Development Arrangement, Contract to Perform for Others [Line Items]      
Research and development expense $ 358us-gaap_ResearchAndDevelopmentExpense
/ us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis
= gd_CompanySponsoredRAndDIncludingProductDevelopmentCostsMember
$ 310us-gaap_ResearchAndDevelopmentExpense
/ us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis
= gd_CompanySponsoredRAndDIncludingProductDevelopmentCostsMember
$ 374us-gaap_ResearchAndDevelopmentExpense
/ us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersByTypeAxis
= gd_CompanySponsoredRAndDIncludingProductDevelopmentCostsMember