Employee benefit plans - allocation of plan assets (Details) - Pension plans - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
United States
Defined benefit plan, information about plan assets
Plan assets	$ 211.4	$ 268.9	$ 286.6
United States | Cash
Defined benefit plan, information about plan assets
Plan assets	5.2	4.2
United States | Fixed income
Defined benefit plan, information about plan assets
Plan assets	164.5	211.7
United States | Equity
Defined benefit plan, information about plan assets
Plan assets	41.7	53.0
United States | Level 1
Defined benefit plan, information about plan assets
Plan assets	5.2	4.2
United States | Level 1 | Cash
Defined benefit plan, information about plan assets
Plan assets	5.2	4.2
United States | Level 1 | Fixed income
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Level 1 | Equity
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Level 2
Defined benefit plan, information about plan assets
Plan assets	206.2	264.7
United States | Level 2 | Cash
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Level 2 | Fixed income
Defined benefit plan, information about plan assets
Plan assets	164.5	211.7
United States | Level 2 | Equity
Defined benefit plan, information about plan assets
Plan assets	41.7	53.0
United States | Level 3
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Level 3 | Cash
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Level 3 | Fixed income
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Level 3 | Equity
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
United States | Fair Value Measured at Net Asset Value Per Share
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S.
Defined benefit plan, information about plan assets
Plan assets	118.6	182.8	167.5
Non-U.S. | Cash
Defined benefit plan, information about plan assets
Plan assets	0.7	1.4
Non-U.S. | Fixed income
Defined benefit plan, information about plan assets
Plan assets	46.1	93.3
Non-U.S. | Equity
Defined benefit plan, information about plan assets
Plan assets	8.9	19.6
Non-U.S. | Other
Defined benefit plan, information about plan assets
Plan assets	19.5	27.1
Non-U.S. | Insurance contracts
Defined benefit plan, information about plan assets
Plan assets	43.4	41.4
Non-U.S. | Level 1
Defined benefit plan, information about plan assets
Plan assets	0.7	1.4
Non-U.S. | Level 1 | Cash
Defined benefit plan, information about plan assets
Plan assets	0.7	1.4
Non-U.S. | Level 1 | Fixed income
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 1 | Equity
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 1 | Other
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 1 | Insurance contracts
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 2
Defined benefit plan, information about plan assets
Plan assets	61.3	125.8
Non-U.S. | Level 2 | Cash
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 2 | Fixed income
Defined benefit plan, information about plan assets
Plan assets	46.1	93.3
Non-U.S. | Level 2 | Equity
Defined benefit plan, information about plan assets
Plan assets	8.9	19.6
Non-U.S. | Level 2 | Other
Defined benefit plan, information about plan assets
Plan assets	6.3	12.9
Non-U.S. | Level 2 | Insurance contracts
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 3
Defined benefit plan, information about plan assets
Plan assets	43.4	41.4	$ 38.3
Non-U.S. | Level 3 | Cash
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 3 | Fixed income
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 3 | Equity
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 3 | Other
Defined benefit plan, information about plan assets
Plan assets	0.0	0.0
Non-U.S. | Level 3 | Insurance contracts
Defined benefit plan, information about plan assets
Plan assets	43.4	41.4
Non-U.S. | Fair Value Measured at Net Asset Value Per Share
Defined benefit plan, information about plan assets
Plan assets	13.2	14.2
Non-U.S. | Fair Value Measured at Net Asset Value Per Share | Other
Defined benefit plan, information about plan assets
Plan assets	$ 13.2	$ 14.2