Employee plans - Additional Information (Detail)	12 Months Ended
Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) plan shares	Dec. 31, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares of unissued common stock available for grant under the plans (in shares) \| shares	5,800,000
Share-based compensation expense	$ 13,200,000	$ 13,200,000	$ 11,200,000
Grants of stock option awards (in shares) \| shares	0	0	0
Stock option awards outstanding (in shares) \| shares	500,000
Weighted-average exercise price of outstanding stock option awards (in dollars per share) \| $ / shares	$ 23.60
Matching contribution by the company as percentage of participants' contribution	50.00%
Percentage of eligible pay contributed by participants that will be matched	6.00%
Cost recognized for contribution plans	$ 12,800,000	$ 11,100,000	$ 10,800,000
Deferred compensation liability	14,700,000	11,600,000
International Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cost recognized for contribution plans	19,300,000	21,300,000	18,500,000
Pension Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated cash contributions by the company in next fiscal year	278,900,000
Pension Plans \| U.S. Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash pension settlement charge	0	$ 0	0
Estimated cash contributions by the company in next fiscal year	238,800,000
Pension Plans \| International Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of defined benefit plans with cash lump-sum payments paid to certain plan participants \| plan		2
Non-cash pension settlement charge	1,200,000	$ 6,400,000	0
Estimated cash contributions by the company in next fiscal year	40,100,000
Other Postretirement Benefit Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Estimated cash contributions by the company in next fiscal year	$ 7,000,000
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Certain investments valued using net asset value as practical expedient, redemption notice period	120 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 13,200,000	13,100,000	10,100,000
Aggregate weighted-average grant-date fair value of units granted	16,900,000	17,900,000	14,400,000
Total unrecognized compensation cost	$ 11,800,000
Unrecognized compensation cost, weighted-average recognition period	1 year 9 months 18 days
Aggregate weighted-average grant-date fair value of units vested	$ 14,900,000	10,400,000	7,400,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 0	$ 100,000	$ 1,100,000
Performance-Based Unit \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares which will vest after achievement of goals (in shares) \| shares	0
Performance-Based Unit \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares which will vest after achievement of goals (in shares) \| shares	2

Defined Benefit Plan, Payments for Settlement, Number of Plans with Cash Lump-Sum Payments

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Matching Contribution By Employer As Percentage Of Participants Contribution

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Share-based compensation arrangement by share-based payment award, other than options, grants in period, weighted average grant date fair value.

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Share-based compensation arrangement by share-based payment award, other than options, vested in period, weighted average grant date fair value.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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The carrying amount of the liability as of the balance sheet date to an individual under a deferred compensation arrangement. This amount may be the result of periodic accruals made over the period of active employment, or reflect termination benefits resulting contractual terms or a death benefit.

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Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

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Amount of cost for defined contribution plan.

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Notice period the entity is required to deliver before it can redeem an investment calculated using net asset value per share, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, investments calculated by per unit, per membership interest, other equity or ownership interest and alternative investments.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Net number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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