Goodwill and Identifiable Intangibles (Goodwill) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Beginning balance		$ 670.3	$ 670.3	$ 587.1
Acquisitions			2.4	106.5
Foreign currency translation			36.2	(23.3)
Ending balance			708.9	670.3
Accumulated impairment losses					$ (215.1)
Goodwill impairment loss	$ 0.0	0.0
ACCO Brands North America
Goodwill [Roll Forward]
Beginning balance		375.6	375.6	380.7
Acquisitions			0.0	(5.1)
Foreign currency translation			0.0	0.0
Ending balance			375.6	375.6
ACCO Brands EMEA
Goodwill [Roll Forward]
Beginning balance		129.4	129.4	39.5
Acquisitions			0.0	113.2
Foreign currency translation			36.2	(23.3)
Ending balance			165.6	129.4
ACCO Brands International
Goodwill [Roll Forward]
Beginning balance		$ 165.3	165.3	166.9
Acquisitions			2.4	(1.6)
Foreign currency translation			0.0	0.0
Ending balance			$ 167.7	$ 165.3