Stockholders' Equity and Earnings Per Common Share - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Option, Exercise Price Range, Outstanding, Weighted Average Exercise Price	$ 24.25		$ 24.25
Outstanding Restricted Stock Unit Grant Prices Lower Limit	12.45		12.45
Outstanding Restricted Stock Unit Grant Prices Upper Limit	$ 55.26		$ 55.26
Antidilutive Securities Excluded from Computation of Earnings Per Share	2,000,000.0	1,200,000	1,600,000	1,200,000
Expiration Date of Share Repurchase Program Authorized in May 2019			Nov. 23, 2020
Number of Treasury Shares Repurchased	0	3,400,000	0	9,000,000.0
Shares Repurchased Cost, Commissions		$ 0.1		$ 0.3
Authorized Shares of Preferred Stock	25,000,000.0		25,000,000.0
Par Value Per Share of Preferred Stock	$ 0.10		$ 0.10
Issued Shares of Preferred Stock	0		0
Repurchase Program Authorized in May 2019
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program	$ 750.0		$ 750.0
Remaining Amount of Treasury Share Repurchases Authorized Under Stock Repurchase Program	516.2		516.2
Repurchase Program Authorized in May 2018
Authorized Amount of Treasury Share Repurchases Under Stock Repurchase Program	$ 750.0		$ 750.0
Open Market Repurchase
Cost of Shares Repurchased		$ 100.1		$ 300.3

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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