Supplemental Cash Flow Information (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
Supplemental Cash Flow Information (Textuals)
Interest paid, net of amounts capitalized			$ 143.4	$ 146.6
Proceeds from Income Tax Refunds				38.3
Income Taxes Paid, Net			22.0
Accounts payable related to capital expenditures	4.9	3.4	4.9	3.4
Amortization of deferred revenue			41.7	42.7
Income (Loss) from Equity Method Investments	18.0	17.1	52.8	51.0
Distributions from transmission affiliate			42.6	40.5
Transmission Affiliate [Member]
Supplemental Cash Flow Information (Textuals)
Income (Loss) from Equity Method Investments	$ 18.0	$ 17.1	$ 52.8	$ 51.0