Unrecognized tax benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Balance at Beginning of Year	$ 138.9	$ 146.8	$ 149.8
Tax Positions Related to Prior Years - Additions	4.4	3.6	8.5
Tax Positions Related to Prior Years - Subtractions	(11.8)	(11.5)	(11.5)
Tax Positions Related to Prior Years - Settlements with Tax Authorities	(44.6)	0	0
Balance at End of Year	86.9	138.9	146.8
Less Tax Attributable to Temporary Items Included Above	(86.9)	(123.7)	(131.6)
Total Unrecognized tax Benefits that if Recognized Would Affect the Effective Tax Rate	$ 0	$ 15.2	$ 15.2