Note 2 - Summary of Significant Accounting Policies - Segment Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Revenues	$ 263,029	$ 46,017
Cost of goods/services	(163,192)	(22,530)
Depreciation and amortization	10,323	7,924
Interest expense	832,408	953,636
Expenditures for assets	18,753
Equipment, net of depreciation	117,295	54,121	$ 108,865
Net loss	(2,429,568)	(2,325,676)
Tangible assets, net	1,231,097	1,464,092
Odor-No-More [Member]
Revenues	224,397	46,017
Cost of goods/services	(134,464)	(22,530)
Depreciation and amortization	4,093	7,924
Interest expense
Expenditures for assets
Equipment, net of depreciation	42,299	54,121
Net loss	(200,000)	(175,000)
Tangible assets, net	293,997	180,292
Clyra Segment [Member]
Revenues
Cost of goods/services
Depreciation and amortization
Interest expense		8,750
Expenditures for assets
Equipment, net of depreciation
Net loss	(198,721)	(137,082)
Tangible assets, net	347,836	268,771
BioLargo Engineering, Science & Technologies, LLC [Member]
Revenues	38,632
Cost of goods/services	(28,728)
Depreciation and amortization	6,230
Interest expense
Expenditures for assets	18,753
Equipment, net of depreciation	74,996
Net loss	(46,387)
Tangible assets, net	140,722
BioLargo/Other [Member]
Revenues
Cost of goods/services
Depreciation and amortization
Interest expense	832,408	944,886
Expenditures for assets
Equipment, net of depreciation
Net loss	(1,984,460)	(2,013,594)
Tangible assets, net	$ 448,542	$ 1,015,039