Income Tax - Additional Information (Detail)	6 Months Ended
Jun. 30, 2013
Income Tax Disclosure [Abstract]
Possible chance of tax position sustained, percentage	50.00%

Possible chance of tax position sustainable, percentage.

No definition available.

Name:	gd_PossibleChanceOfTaxPositionSustainablePercentage
Namespace Prefix:	gd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration