Supplemental Cash Flow Information - Schedule of Cash and Cash Equivalents (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure Supplemental Cash Flow Information [abstract]
Cash	$ 184	$ 146
Short-term money market investments	2	11
Total	$ 186	$ 157

Disclosure Supplemental Cash Flow Information [abstract]

No definition available.

Name:	gg_DisclosureSupplementalCashFlowInformationAbstract
Namespace Prefix:	gg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash on hand and demand deposits. [Refer: Cash on hand]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2017-01-01
-Paragraph 45
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=7&date=2017-03-01&anchor=para_45&doctype=Standard
-URIDate 2017-03-09

+ Details

Name:	ifrs-full_Cash
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of short-term, highly liquid investments that are readily convertible to known amounts of cash and that are subject to an insignificant risk of changes in value.

+ References

+ Details

Name:	ifrs-full_CashEquivalents
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

A classification of cash equivalents representing short-term investments. [Refer: Cash equivalents]

+ References

+ Details

Name:	ifrs-full_ShorttermInvestmentsClassifiedAsCashEquivalents
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant