Earnings Per Share - Schedule of Computations of Weighted Average Shares Outstanding (Detail) - shares shares in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Weighted-average shares outstanding	423.2	473.3	485.7
Share-based payment awards classified as participating securities	0.1	0.4	1.0
Basic weighted-average shares outstanding	423.3	473.7	486.7
Dilutive securities	0.6	0.0	1.3
Diluted weighted-average shares outstanding	423.9	473.7	488.0
Share Based Awards
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Potentially dilutive restricted share awards excluded from computation of diluted EPS		0.6

Dilutive securities excluded from computation of earnings per share, amount.

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- Definition

This element represents the weighted average shares outstanding throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period.

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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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This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method.

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- Definition

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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