INCOME TAXES - EFFECTIVE INCOME TAX RECONCILIATION (DETAILS) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	35.00%	35.00%	35.00%
Income before income tax	$ 393.7	$ 405.9	$ 202.9
Expected tax expense	137.8	142.1	71.0
Nondeductible expenses	1.4	1.8	3.1
State income taxes	10.2	10.7	5.5
Other—net	(0.2)	0.2	1.7
Total tax expense related to income	$ 149.2	$ 154.8	$ 81.3
Effective tax rate	37.90%	38.10%	40.10%