Capital Stock - Additional Information (Detail) - USD ($)	12 Months Ended			147 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Oct. 27, 2006
Class of Stock [Line Items]
Aggregate common stock and preferred stock authorized	300,000,000			300,000,000
Common stock, authorized	250,000,000	250,000,000		250,000,000
Common stock, par value	$ 1	$ 1.00		$ 1
Preferred Stock, authorized	50,000,000			50,000,000
Preferred Stock, outstanding	0	0		0
Dividends declared per common share	$ 0.536	$ 0.512	$ 0.496
Share repurchase program					$ 1,000,000,000
Shares purchased under share repurchase program	1,000,000.0	800,000	2,000,000.0	22,200,000
Cost of shares repurchased under share repurchase program	$ 56,100,000	$ 32,900,000	$ 77,800,000	$ 909,400,000
Common Stock [Member]
Class of Stock [Line Items]
Shares purchased under share repurchase program	1,100,000	900,000	2,200,000
Cost of shares repurchased under share repurchase program	$ 1,100,000	$ 900,000	$ 2,200,000
Share Repurchase Program [Member]
Class of Stock [Line Items]
Cost of shares repurchased under share repurchase program	$ 50,000,000.0	$ 30,000,000.0	$ 70,000,000.0
Settlement of Tax Withholding on Employee Equity Compensation [Member]
Class of Stock [Line Items]
Shares purchased under share repurchase program	100,000	100,000	200,000
Cost of shares repurchased under share repurchase program	$ 6,100,000	$ 2,900,000	$ 7,800,000