Shareholders' Equity Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Repurchase and retirement of common stock	$ 111.4	$ 0.5	$ 410.5	$ 49.3
Repurchase and retirement of common stock (shares)			3.3
Stock Repurchase Program, Number of Shares Authorized to be Repurchased	888.8		888.8
Cash dividend paid during period, per share (in dollars per share)	$ 0.63	$ 0.62	$ 1.26	$ 1.24
Common stock excluded from calculation of diluted earnings per share (shares)	0.6	5.3	0.8	5.2
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)		0.5		0.6