Investments (Summary Financial Information) (Details) (American Transmission Company LLC (ATC) [Member], USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
American Transmission Company LLC (ATC) [Member]
Operating revenues	$ 142.8	$ 136.8	$ 420.6	$ 414.0
Operating income	76.4	77.2	228.1	229.0
Net income	$ 56.6	$ 55.0	$ 166.5	$ 164.2

The amount of gross profit (loss) reported by an equity method investment of the entity.

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+ Details

- Definition

The amount of net income (loss) reported by an equity method investment of the entity.

+ References

+ Details