Provision for Income Taxes Reconciles with U.S. Federal Statutory Rate (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Statutory Federal Tax Rate [Line Items]
Provision for income taxes	$ 7.3	$ 168.0	$ 131.9	$ 106.6
Effective income tax rate reduction	2.10%