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Income Taxes - Additional Information (Details) | Jul. 01, 2018 USD ($)
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Income Tax Disclosure [Abstract] |
Possible chance of tax position sustained, percentage | 50.00%
Amount of unrecorded benefit | $ 0

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- Definition Possible chance of tax position sustainable, percentage. + References No definition available. + Details
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Namespace Prefix: | gd_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of the unrecognized tax benefit of a position taken for which it is reasonably possible that the total amount thereof will significantly increase or decrease within twelve months of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant