Commitments And Contingencies (Third-Party Power Purchase Agreements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Qualifying Facilities [Member]
Third-Party Power Purchase Agreements [Line Items]
Long term contract for purchase commitments, date of contract expiration, beginning date	2016
Long term contract for purchase commitments, date of contract expiration, ending date	2028
Present value of fixed capacity payments, portion classified as current liabilities	$ 19.0	$ 20.0
Present value of fixed capacity payments, portion classified as noncurrent liabilities	35.0	54.0
Capitalized asset for fixed capacity payments for corresponding assets	54.0	74.0
Capitalized asset for fixed capacity payments, accumulated amortization	$ 147.0	128.0
Renewable Energy [Member]
Third-Party Power Purchase Agreements [Line Items]
Long term contract for purchase commitments, date of contract expiration, beginning date	2016
Long term contract for purchase commitments, date of contract expiration, ending date	2043
Power Purchases and Electric Capacity [Member]
Third-Party Power Purchase Agreements [Line Items]
Long term contract for purchase commitments, date of contract expiration, beginning date	2016
Long term contract for purchase commitments, date of contract expiration, ending date	2033
Costs Of Power Purchase	$ 3.5	$ 3.6	$ 3.0