Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Tax Contingency [Line Items]
Effective tax rate	29.50%	28.50%	31.70%	29.90%
Overall increase (decrease) in unrecognized tax benefits (UTPs)			$ (61.5)	$ (0.1)
Gross
Income Tax Contingency [Line Items]
Overall increase (decrease) in unrecognized tax benefits (UTPs)	14.6		60.8
Net of Federal Tax Benefits
Income Tax Contingency [Line Items]
Overall increase (decrease) in unrecognized tax benefits (UTPs)	12.1		$ 33.5