INVESTMENTS IN AFFILIATES, AT EQUITY METHOD (Details 3) (ATC INDU Solar Holdings LLC and WRPC, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
ATC INDU Solar Holdings LLC and WRPC
Income statement data
Revenues	$ 575.5	$ 564.1	$ 528.7
Operating expenses	269.6	257.6	235.7
Other expense	81.5	85.7	77.7
Net income	224.4	220.8	215.3
Add: Equity in net income (loss)	79.4	78.2	76.3
Balance sheet data
Current assets	91.1	62.7	54.0
Noncurrent assets	3,120.5	2,906.2	2,785.5
Total assets	3,211.6	2,968.9	2,839.5
Current liabilities	319.9	429.0	286.3
Long-term debt	1,400.0	1,175.0	1,259.6
Other noncurrent liabilities	88.0	88.5	80.1
Shareholders' equity	1,403.7	1,276.4	1,213.5
Total liabilities and shareholders' equity	$ 3,211.6	$ 2,968.9	$ 2,839.5