Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Repurchase and retirement of common stock	$ 0.8	$ 0.2	$ 411.3	$ 49.5
Repurchase and retirement of common stock (shares)			3.3
Number of shares authorized to be repurchased (in shares)	888.8		888.8
Cash dividend paid during period, per share (in dollars per share)	$ 0.63	$ 0.62	$ 1.89	$ 1.86
Common stock excluded from calculation of diluted earnings per share (shares)	0.8	2.2	0.8	5.0
Omnibus Incentive Plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock excluded from calculation of diluted earnings per share (shares)				0.7