Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Computation of Basic and Diluted Income Per Common Share

The following table sets forth the computation of basic and diluted income per common share for the periods presented (dollars and shares in millions, except per share data).

	Year Ended December 31,
		2020			2019			2018
Numerator:
Net income	$	461.0		$	696.4		$	738.0
Less: distributed and undistributed earnings allocated    to participating securities		(3.6	)		(5.2	)		(5.7	)
Net income attributable to common stockholders	$	457.4		$	691.2		$	732.3
Denominator:
Weighted average common shares outstanding		94.1			93.8			93.7
Effect of dilutive securities		0.3			0.3			0.2
Diluted common shares outstanding		94.4			94.1			93.9
Basic income per common share	$	4.86		$	7.36		$	7.82
Diluted income per common share	$	4.84		$	7.34		$	7.80