Supplemental Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Supplemental Cash Flow Information (Textuals)
Interest paid, net of amounts capitalized	$ 3.6
Income taxes paid, net of refunds	2.0	9.2
Interest Paid		0.9
Interest Costs Capitalized		6.1
Accounts payable related to capital expenditures	8.8	12.5
Income (Loss) from Equity Method Investments	14.7	13.7
Distributions from transmission affiliate	$ 11.7	$ 11.3