CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
CONSOLIDATED BALANCE SHEETS
Accumulated Depreciation on Property, Plant, and Equipment	$ 268.8	$ 236.3
Accumulated amortization on power purchase agreements and other intangible assets	271.0	238.0
Accumulated amortization on power purchase and fuel supply agreement liabilities	$ 15.4	$ 14.0
Common shares, no par value (in dollars per share)	$ 0	$ 0
Common Stock, Shares Authorized, Unlimited	Unlimited	Unlimited
Common shares, issued shares (in shares)	120,682,964	122,153,082
Common shares, outstanding shares (in shares)	120,682,964	122,153,082