SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 M	Dec. 31, 2010	Dec. 31, 2009
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
Reclassification of amount reported in other current assets in previous period to prepaid taxes		$ 127.2
Cash and Cash Equivalents
Maximum term of original maturity to classify instruments as cash equivalent (in months)	3
Supplemental disclosure of statements of cash flows
Cash paid for interest	130.7	138.7	164.8
Cash (received) paid for income taxes	(80.0)	(2.2)	19.1
Significant noncash transactions
Construction costs funded through accounts payable	58.6	18.3	30.4
Equity issued for stock-based compensation plans	15.8	3.0
Equity issued for reinvested dividends	5.4	22.6
Intangible assets (customer contracts) received in exchange for risk management assets			$ 17.0