Financial Instruments (Narrative) (Details) - USD ($)	Jul. 01, 2016	Dec. 31, 2015
Derivative Instruments and Hedges, Assets [Abstract]
Derivative contracts held that require collateral securities	$ 0	$ 0

Derivative Contracts Held that Require Collateral Securities

No definition available.

Name:	bgc_DerivativeContractsHeldthatRequireCollateralSecurities
Namespace Prefix:	bgc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant