EQUITY METHOD INVESTMENTS (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments in affiliates, at equity method
Equity method investments	$ 540.9	$ 512.2
ATC
Investments in affiliates, at equity method
Equity method investments	508.4	476.6	439.4	416.3
INDU Solar Holdings, LLC
Investments in affiliates, at equity method
Equity method investments	24.7	27.5	28.4	0.1
WRPC
Investments in affiliates, at equity method
Equity method investments	7.0	7.3	7.7	8.1
Other
Investments in affiliates, at equity method
Equity method investments	$ 0.8	$ 0.8