INVESTMENT IN ATC - ROLL FORWARD (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Changes in equity method investments
Equity method investments balance at beginning of period			$ 540.9
Add: Earnings from equity method investment	24.5	23.1	71.3	68.2
Add: Capital contributions			14.6	10.2
Equity method investments balance at end of period	568.9		568.9
ATC
Investments in affiliates, at equity method
Equity method investment, ownership interest (as a percent)	34.00%		34.00%
Changes in equity method investments
Equity method investments balance at beginning of period	527.3	492.2	508.4	476.6
Add: Earnings from equity method investment	23.4	22.3	68.9	66.0
Add: Capital contributions	3.4	3.4	13.6	10.2
Less: Dividends received	18.5	17.8	55.3	52.7
Equity method investments balance at end of period	$ 535.6	$ 500.1	$ 535.6	$ 500.1

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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