Capital Stock - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2018	Feb. 28, 2017
Equity Class Of Treasury Stock [Line Items]
Total cost of shares repurchased	$ 357,700,000	$ 150,300,000	$ 111,100,000
Dividends paid on common stock	48,400,000	$ 42,600,000	$ 39,800,000
Dividends per share of common stock		$ 0.47	$ 0.44
2018 Repurchase Plan
Equity Class Of Treasury Stock [Line Items]
Authorized amount to repurchase outstanding common stock				$ 500,000,000
Remaining authorized amount to repurchase outstanding common stock	384,800,000
2017 Repurchase Plan
Equity Class Of Treasury Stock [Line Items]
Authorized amount to repurchase outstanding common stock					$ 300,000,000
Total cost of shares repurchased	$ 242,500,000