Business Combination (Purchase Price Allocation Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Current [Member]
Cash	$ 116.4
Restricted Cash	18.5
Accounts receivable	277.6
Inventory	123.7
Other current assets	37.3
Property, plant and equipment	2,477.8
Intangible assets subject to amortization	147.2
Intangible assets - indefinite-lived	5.0
Regulatory assets	217.1
Other non-current assets	58.3
Current liabilities	(413.1)
Debt	(1,255.1)
Deferred taxes	(551.2)
Regulatory liabilities	(117.0)
Other non-current liabilities	(216.8)
Redeemable preferred stock	(18.4)
Net Identifiable Assets Acquired, Total	(907.3)
Goodwill	2,576.3
Net assets acquired	3,483.6
Preliminary [Member]
Cash	116.4
Restricted Cash	18.5
Accounts receivable	277.6
Inventory	123.7
Other current assets	37.3
Property, plant and equipment	2,548.5
Intangible assets subject to amortization	166.3
Intangible assets - indefinite-lived	5.0
Regulatory assets	201.1
Other non-current assets	58.3
Current liabilities	(408.2)
Debt	(1,255.1)
Deferred taxes	(558.2)
Regulatory liabilities	(117.0)
Other non-current liabilities	(201.5)
Redeemable preferred stock	(18.4)
Net Identifiable Assets Acquired, Total	(994.3)
Goodwill	2,489.3
Net assets acquired	$ 3,483.6