Net Earnings (Loss) per Common Share - Calculation of Basic and Diluted Net Earnings (Loss) Per Common Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013		Dec. 31, 2012
Numerator
Net earnings (loss)	$ 66.3	$ 60.8	$ 60.1	$ 70.9	$ 29.0	$ 38.0	$ 54.7	$ 4.1	$ 258.1	$ 125.8	[1]	$ (1,411.4)	[1]
Distributed and allocated undistributed net loss to non-vested restricted stockholders									(1.6)	(0.7)		(0.5)
Distributed and allocated undistributed net earnings (loss) to common stockholders									256.5	125.1		(1,411.9)
Distributed net earnings - dividends paid to common stockholders									(110.1)	(101.3)		(100.4)
Allocation of undistributed net earnings (loss) to common stockholders									146.4	23.8		(1,512.3)
Denominator
Weighted average number of common shares outstanding - basic									210.0	194.6	[1]	192.8	[1]
Basic net earnings (loss) per common share:
Distributed net earnings to common stockholders									$ 0.52	$ 0.52		$ 0.52
Allocated undistributed net earnings (loss) to common stockholders									$ 0.70	$ 0.13		$ (7.84)
Net earnings (loss) per common share - basic	$ 0.31	$ 0.29	$ 0.28	$ 0.34	$ 0.15	$ 0.19	$ 0.28	$ 0.02	$ 1.22	$ 0.65	[1]	$ (7.32)	[1]
Numerator
Distributed and allocated undistributed net earnings (loss) to common stockholders									256.5	125.1		(1,411.9)
Add: Allocated undistributed net earnings to non-vested restricted stockholders									1.0	0.2
Less: Undistributed net earnings (loss) reallocated to non-vested restricted stockholders									(0.9)	(0.1)
Net earnings (loss) available to common stockholders - diluted									$ 256.6	$ 125.2		$ (1,411.9)
Denominator
Weighted average number of common shares outstanding - basic									210.0	194.6	[1]	192.8	[1]
Effect of assumed issuance of Settlement agreement shares									1.6	18.0
Effect of contingently issuable shares									0.9	0.7
Effect of non-vested restricted stock units									1.4	0.9
Weighted average number of common shares outstanding - diluted									213.9	214.2	[1]	192.8	[1]
Net earnings (loss) per common share - diluted	$ 0.31	$ 0.28	$ 0.28	$ 0.33	$ 0.13	$ 0.18	$ 0.25	$ 0.02	$ 1.20	$ 0.58	[1]	$ (7.32)	[1]

[1] Certain amounts have been revised to reflect the retrospective application of the Company’s change in inventory costing method for certain U.S. inventories to the FIFO method from the LIFO method. Refer to Note 2, “Summary of Significant Accounting Policies - Inventories,” of the notes to consolidated financial statements for further details surrounding this accounting policy change.