Stock-Based Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 24.2	$ 23.5	$ 25.2
Allocated Share-based Compensation Expense, Net of Tax	15.6	15.3	17.2
nonvestedstockawardsandcashsettledawards [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	20.9	19.6	20.7
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	2.7	2.7	2.5
Employee Stock Ownership Plan (ESOP), Plan [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 0.6	$ 1.2	$ 2.0