Average Remaining Expected Working Life of Plan Participants

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Average Remaining Life Expectancy of Plan Participants

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Defined Contribution Plan, Employer Discretionary Contribution Percentage of Earnings

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Defined Contribution Plan, Maximum Employee Contribution Eligible for Matching

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Defined Contribution Plan, Minimum Employee Contribution Eligible for Matching

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Pension and Other Postretirement Benefits Disclosure [Line Items]

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Private Equity Partnership Future Liquidation Term

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The average effective interest rate during the reporting period.

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Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

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Ultimate trend rate for health care cost for defined benefit postretirement plan.

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Year ultimate health care cost trend rate is expected to be reached, in YYYY format.

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Amount of cost for defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Pension and Other Postretirement Benefits Disclosure
Health Care Cost Trend Rate Assumed for Next Fiscal Year	7.00%	6.25%
Ultimate Health Care Cost Trend Rate	5.00%
Defined Benefit Plan, Year Health Care Cost Trend Rate Reaches Ultimate Trend Rate	2031
Pension Plan \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Average Remaining Life Expectancy of Plan Participants	24 years
Alternative Investments, Unfunded Commitments	$ 24.5	$ 28.5
Pension Plan \| UNITED KINGDOM
Pension and Other Postretirement Benefits Disclosure
Average Remaining Life Expectancy of Plan Participants	28 years
Alternative Investments, Unfunded Commitments	$ 17.3	28.1
Other Postretirement Benefit Plans
Pension and Other Postretirement Benefits Disclosure
Average Remaining Expected Working Life of Plan Participants	2 years
Investment Level 3 Transfers Into	$ 0.0	0.0
Investment Level 3 Transfers Out of	$ 0.0	$ 0.0
Interest Rate During Period	4.31%	4.59%
Other Postretirement Benefit Plans \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay	5.00%
Employer Discretionary Contribution Percentage of earnings	4.50%
Cost Recognized	$ 70.9	$ 71.0	$ 83.4
Other Postretirement Benefit Plans \| UNITED KINGDOM
Pension and Other Postretirement Benefits Disclosure
Defined Contribution Plan, Minimum Employee Contribution Eligible for Matching	1.00%
Defined Contribution Plan, Maximum Employee Contribution Eligible for Matching	5.00%
Cost Recognized	$ 4.9	$ 4.9	$ 5.0
Equity Securities \| Pension Plan \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	38.00%
Fixed Maturity Securities \| Pension Plan \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	30.00%
Diversified Growth Assets \| Pension Plan \| UNITED KINGDOM
Pension and Other Postretirement Benefits Disclosure
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Alternative Investments \| Pension Plan \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	32.00%
Fixed Income and Index-linked Securities \| Pension Plan \| UNITED KINGDOM
Pension and Other Postretirement Benefits Disclosure
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Minimum \| Other Postretirement Benefit Plans \| UNITED KINGDOM
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay	8.00%
Minimum \| Private Equity Funds of Funds \| Pension Plan \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	5 years
Maximum \| Other Postretirement Benefit Plans \| UNITED KINGDOM
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay	12.00%
Maximum \| Private Equity Funds of Funds \| Pension Plan \| UNITED STATES
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	8 years