Computation of Basic and Diluted Net Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share Disclosure [Line Items]
Numerator: net earnings	$ 75.2	[1]	$ 18.5	[1]	$ 71.2	[1]	$ 68.8	[1]	$ 57.3		$ 65.4		$ 54.8		$ 50.3		$ 233.7	$ 227.8	$ 143.3
Denominator:
Denominator for basic earnings per share - Weighted average shares (in millions)																	102.2	101.1	99.7
Effect of dilutive securities - Dilutive securities																	0.7	0.8	1.2
Denominator for diluted earnings per share - Adjusted weighted average shares (in millions)																	102.9	101.9	100.9
Basic net earnings per share	$ 0.73	[2]	$ 0.18	[2]	$ 0.70	[2]	$ 0.67	[2]	$ 0.57	[2]	$ 0.65	[2]	$ 0.54	[2]	$ 0.50	[2]	$ 2.29	$ 2.25	$ 1.44
Diluted net earnings per share	$ 0.73	[2]	$ 0.18	[2]	$ 0.69	[2]	$ 0.67	[2]	$ 0.56	[2]	$ 0.64	[2]	$ 0.54	[2]	$ 0.49	[2]	$ 2.27	$ 2.24	$ 1.42

[1] Third quarter 2012 net earnings reflect debt prepayment costs of $82.1.

[2] Net earnings per share are computed individually for each quarter presented. Therefore, the sum of the quarterly net earnings per share may not necessarily equal the total for the year.