Components of Stock Based Compensation (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 5.3		$ 5.5		$ 13.4		$ 14.8
Employee contributions for above stock plans	2.5		2.3		4.9		6.3
Total stock-based compensation	7.8		7.8		18.3		21.1
Recognized tax benefits on stock-based compensation expense	2.0		2.1		5.1		5.6
Amortization Of The Grant Date Fair Value Of Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0.9	[1]	0.8	[1]	3.2	[1]	3.6	[1]
Stock-Based Retirement Plans Contributions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1.4	[2]	1.4	[2]	3.3	[2]	3.5	[2]
Deferred Stock Compensation Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0.1		0.2		0.6		0.8
Stock-Based Retirement Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0.2		0.3		0.7		1.2
Discount Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0.3		0.2		0.5		0.4
Performance Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1.6	[3]	1.8	[3]	3.3	[3]	3.6	[3]
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0.6		0.6		1.4		1.1
Other, Primarily Non-Employee Directors Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 0.2		$ 0.2		$ 0.4		$ 0.6

[1] Stock Option Grants

[2] Stock-Based Retirement Plans

[3] Performance Stock Unit Awards