Redemption Payable To Managing Owner (Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Redemption Payable To Managing Owner [Abstract]
Redemption payable	$ 68,133	$ 308,812

Profit Share Allocated To Managing Owner Including Profit And Loss

No definition available.

Name:	millgmt_ProfitShareAllocatedToManagingOwnerIncludingProfitAndLoss
Namespace Prefix:	millgmt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration