Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) - shares shares in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Weighted-average shares used in basic computations	137.1	145.3
Dilutive effect of exercise of equity grants outstanding	4.5	7.4
Dilutive effect of 2019 Convertible Notes	3.9
Weighted-average shares used in diluted computations	145.5	152.7

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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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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