Note 2 - Summary of Significant Accounting Policies - Segment Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenues	$ 277,026	$ 172,045	$ 866,793	$ 318,040
Cost of goods/services	(121,546)	(123,278)	(485,650)	(219,207)
Net loss	(2,379,735)	(2,246,126)	(8,409,213)	(7,145,868)
Assets, net	1,088,885		1,088,885		$ 1,495,420
Odor-No-More [Member]
Revenues	245,979	172,045	785,929	318,040
Cost of goods/services	(97,578)	(123,278)	(426,042)	(219,207)
Net loss	(111,963)	(112,500)	(365,651)	(387,500)
Assets, net	231,216		231,216		210,725
BioLargo Engineering, Science & Technologies, LLC [Member]
Revenues	31,047		80,864
Cost of goods/services	(23,968)		(59,608)
Net loss	(63,555)		(180,281)
Assets, net	150,087		150,087
Clyra Segment [Member]
Net loss	(219,971)	(223,610)	(596,333)	(708,182)
Assets, net	25,807		25,807		528,543
BioLargo/Other [Member]
Net loss	(1,984,246)	$ (1,910,016)	(7,266,948)	$ (6,050,186)
Assets, net	$ 681,775		$ 681,775		$ 756,152