Net Earnings (Loss) Per Common Share - Calculation of Basic and Diluted Net Earnings Per Common Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator
Net earnings available to common stockholders	$ 71.8	$ 2.7
Distributed and allocated undistributed net earnings to non-vested restricted stockholders	(0.4)	(0.1)
Distributed and allocated undistributed net earnings to common stockholders	71.4	2.6
Distributed net earnings - dividends paid to common stockholders	(27.7)	(25.3)
Allocation of undistributed net earnings to common stockholders	43.7	(22.7)
Denominator
Weighted average number of common shares outstanding - basic	206.7	193.8
Basic net earnings per common share:
Distributed net earnings to common stockholders	$ 0.13	$ 0.13
Allocated undistributed net earnings (loss) to common stockholders	$ 0.22	$ (0.12)
Net earnings per common share-basic	$ 0.35	$ 0.01
Numerator
Distributed and allocated undistributed net earnings to common stockholders	71.4	2.6
Add: Allocated undistributed net earnings to non-vested restricted stockholders	0.3
Less: Undistributed net earnings reallocated to non-vested restricted stockholders	(0.3)
Net earnings available to common stockholders - diluted	$ 71.4	$ 2.6
Denominator
Weighted average number of common shares outstanding - basic	206.7	193.8
Effect of assumed issuance of Settlement agreement shares	6.6	18.0
Effect of non-vested restricted stock units	1.2	0.9
Weighted average number of common shares outstanding - diluted	214.5	212.7
Diluted net earnings per common share	$ 0.33	$ 0.01