Defined contribution and defined benefit retirement - Schedule of Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss) (Detail) - Pension Plans Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Net actuarial gains	$ (25.5)	$ 134.1	$ 50.7
Amortization of unrecognized net actuarial losses	3.8	14.7	21.6
Amortization of unrecognized prior service cost (credit)		0.1	0.2
Settlements	6.5	0.4
Total	$ (15.2)	$ 149.3	$ 72.5