Additional common stock units for election of deferred annual incentive award, percentage.

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Age for eligible employee.

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Allocated share based compensation expense (income).

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Stock option exercise price as percentage of market value.

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The period in which a stock option can be exercised.

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

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Aggregate number of common shares reserved for future issuance.

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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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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares authorized for issuance under share-based payment arrangement.

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Amount of noncash expense for option under share-based payment arrangement.

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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 14, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercise prices as percentage of the market value on the date of the grant	100.00%
Total intrinsic value of stock options exercised	$ 3.3	$ 7.7	$ 12.6
Total aggregate intrinsic value of stock options	19.3
Total aggregate intrinsic value of stock option exercisable	$ 13.3
Grant date fair value of stock options granted	$ 7.56	$ 8.69	$ 15.07
Compensation expenses for stock options	$ 2.7	$ 4.7	$ 4.6
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period	3 years
Stock options term, years	10 years
Unrecognized compensation expense related to stock	$ 2.5
Weighted-average recognition period for unrecognized compensation expense related to stock (years)	2 years 2 months 12 days
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock	$ 53.7
Weighted-average recognition period for unrecognized compensation expense related to stock (years)	1 year 3 months 18 days
Compensation expense	$ 58.6	69.1	54.3
Total fair value of shares, vested	$ 49.8	58.8	54.4
Omnibus Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, common stock available for grant	7,800,000
Omnibus Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation, common stock available for grant				19,000,000.0
LTIP [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible age of officer for restricted stock award	55 years
AIP [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Eligible age of officer for restricted stock award	55 years
Additional common stock units for election of deferred annual incentive award, percentage	25.00%
AIP and LTIP [Member] \| Restricted Stock Awards and Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to stock	$ 1.2
Weighted-average recognition period for unrecognized compensation expense related to stock (years)	1 year 6 months
Total fair value of shares, vested	$ 13.5	17.3	14.7
Compensation expense	$ 12.5	$ 16.6	$ 14.6
Inactive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for future issuance	700,000