Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loss that will be amortized from accumulated other comprehensive income in the next year	$ 0.7
Unrecognized net gains and losses from all sources, threshold	10.00%
Estimated future benefit payments 2016	$ 16.0
Estimated future benefit payments 2017	16.1
Estimated future benefit payments 2018	16.2
Estimated future benefit payments 2019	16.7
Estimated future benefit payments 2020	16.9
Estimated future benefit payments, from 2021 to 2023	88.4
Net defined contribution plan expense recognized	11.7	$ 12.0	$ 11.7
Pension Plan, Defined Benefit [Member]
Loss that will be amortized from accumulated other comprehensive income in the next year	(8.4)
U.S. Plans [Member]
Accumulated benefit obligation	$ 174.2	190.1
Fixed-income investments, expected real rate of return	2.00%
Long-term rate of inflation	3.00%
Discount rate used to determine net postretirement benefit expense	4.30%
Settlement (gain) loss	$ 0.0	0.0	0.0
Defined benefit pension plan cash contributions	$ 5.1	$ 2.1
Discount rate used to determine accumulated postretirement benefit obligation	4.30%	4.02%
Non-U.S. Plans [Member]
Accumulated benefit obligation	$ 110.4	$ 117.9
Discount rate used to determine net postretirement benefit expense	2.81%
Settlement (gain) loss	$ (0.9)	(2.7)	$ (0.1)
Defined benefit pension plan cash contributions	$ 8.3	$ 5.4
Discount rate used to determine accumulated postretirement benefit obligation	2.81%	2.93%
Two Mutual Funds [Member]
Plan assets concentration	43.00%
Debt Securities [Member] \| U.S. Plans [Member]
Asset allocation assumption to equity investments	35.00%
Equity investments, expected real rate of return	8.00%
Equity investment, actual asset allocation	35.00%	31.00%
Debt Securities [Member] \| Non-U.S. Plans [Member]
Asset allocation assumption to equity investments	40.00%	38.00%
Actual asset allocation of fixed-investments	39.00%
Other Investments [Member] \| Non-U.S. Plans [Member]
Actual asset allocation of other investments		3.00%
Equity Securities [Member] \| U.S. Plans [Member]
Asset allocation assumption to equity investments	65.00%
Equity investment, actual asset allocation	65.00%	69.00%
Equity Securities [Member] \| Non-U.S. Plans [Member]
Asset allocation assumption to equity investments	60.00%	59.00%
Actual asset allocation of equity investment	61.00%
Minimum [Member]
Estimated future benefit payments 2016	$ 5.1

Defined Benefit Plan Assets Concentration

No definition available.

Name:	bgc_DefinedBenefitPlanAssetsConcentration
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Defined Benefit Plan, Assumed Long-Term Inflation Rate

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanAssumedLongTermInflationRate
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted Average Discount Rate

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostWeightedAverageDiscountRate
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Benefit Plan, Investment Gains (Losses), Recognition to Benefit Cost, Threshold, Percentage

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanInvestmentGainsLossesRecognitionToBenefitCostThresholdPercentage
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Benefit Plan, Target Allocation Percentage of Assets, Debt Securities, Expected Real Rate of Return

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanTargetAllocationPercentageOfAssetsDebtSecuritiesExpectedRealRateOfReturn
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Benefit Plan, Target Allocation Percentage of Assets, Equity Securities, Expected Real Rate of Return

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanTargetAllocationPercentageOfAssetsEquitySecuritiesExpectedRealRateOfReturn
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Defined Benefit Plan, Weighted Average Asset Allocation of Equity Investments

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanWeightedAverageAssetAllocationOfEquityInvestments
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Defined Benefit Plan, Weighted Average Asset Allocation of Fixed Income Investments

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanWeightedAverageAssetAllocationOfFixedIncomeInvestments
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Defined Benefit Plan, Weighted Average Asset Allocation of Other Investments

+ References

No definition available.

+ Details

Name:	bgc_DefinedBenefitPlanWeightedAverageAssetAllocationOfOtherInvestments
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Accumulated Benefit Obligation
-URI http://asc.fasb.org/extlink&oid=6503844

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation).

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The interest rate used to adjust for the time value of money for the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References