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Retirement Plans (Hypothetical Changes In The Discount Rate And Expected Long-Term Rate Of Return On Plan Assets) (Details) (Pension Benefits, USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Pension Benefits
 
Increase (decrease) to net pension cost from:  
Change in discount rate (increase 25 basis points) $ (29)gd_DefinedBenefitPlanEffectOfPointTwentyFivePercentagePointIncreaseInDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Change in discount rate (decrease 25 basis points) 30gd_DefinedBenefitPlanEffectOfPointTwentyFivePercentagePointDecreaseInDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Change in discount rate of return on plan assets (increase of 25 basis points) (18)gd_DefinedBenefitPlanEffectOfPointTwentyFivePercentagePointIncreaseInLongTermRateOfReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
Change in long-term rate of return on plan assets (decrease 25 basis points) $ 18gd_DefinedBenefitPlanEffectOfPointTwentyFivePercentagePointDecreaseInLongTermRateOfReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember