Unrecognized tax benefits (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Balance at Beginning of Year	$ 86.9	$ 138.9	$ 146.8
Tax Positions Related to Prior Years - Additions	13.3	4.4	3.6
Tax Positions Related to Prior Years - Subtractions	(0.6)	(11.8)	(11.5)
Settlements with Tax Authorities	(23.5)	(44.6)	0
Lapses of Statute of Limitations	(61.1)	0	0
Tax Positions Taken During Current Year	2.5	0	0
Balance at End of Year	17.5	86.9	138.9
Less Tax Attributable to Temporary Items Included Above	(15.0)	(86.9)	(123.7)
Total Unrecognized Tax Benefits that if Recognized Would Affect the Effective Tax Rate	$ 2.5	$ 0	$ 15.2