Pension and Other Retiree Benefits - Net Periodic Benefit Expense (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Pension | U.S.
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0.0	$ 0.0	$ 0.0	$ 0.0
Interest cost		1.9	2.0	3.8	4.0
Expected return on plan assets		(3.2)	(3.0)	(6.4)	(6.0)
Amortization of net loss (gain)		0.6	0.6	1.2	1.2
Amortization of prior service cost		0.0	0.0	0.0	0.0
Settlement	[1]	0.0	0.0	0.0	0.0
Net periodic benefit (income) cost	[2]	(0.7)	(0.4)	(1.4)	(0.8)
Pension | International
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.2	0.1	0.4	0.2
Interest cost		4.6	5.0	9.2	9.9
Expected return on plan assets		(4.9)	(5.4)	(9.7)	(10.7)
Amortization of net loss (gain)		1.3	1.1	2.6	2.1
Amortization of prior service cost		0.1	0.1	0.1	0.2
Settlement	[1]	4.4	0.0	4.4	0.0
Net periodic benefit (income) cost	[2]	5.7	0.9	7.0	1.7
Post-retirement
Defined Benefit Plan Disclosure [Line Items]
Service cost		0.0	0.0	0.0	0.0
Interest cost		0.0	0.0	0.0	0.0
Expected return on plan assets		0.0	0.0	0.0	0.0
Amortization of net loss (gain)		(0.1)	(0.1)	(0.2)	(0.2)
Amortization of prior service cost		0.0	0.0	0.0	0.0
Settlement	[1]	0.0	0.0	0.0	0.0
Net periodic benefit (income) cost	[2]	$ (0.1)	$ (0.1)	$ (0.2)	$ (0.2)

[1] Settlement of $4.4 million resulting from the wind-up of the ACCO Brands Canada Salaried and Hourly pension plans being completed in the second quarter of 2024.

[2] The components of net periodic benefit (income) cost, other than service cost, are included in the line "Non-operating pension expense" in the Consolidated Statements of (Loss) Income.