Quarterly Financial Information (Unaudited) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information [Line Items]
Litigation Charge	$ 137.8
Net discrete tax benefit		5.5	10.5	6.4	16.0	6.8	16.8
Net litigation charge	$ 87.1