Income Tax Expense (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	$ 0	[1]	$ 0	[1]	$ 1.4	[1]
Current State Tax Expense (Benefit)	0.1	[1]	0.5	[1]	(1.6)	[1]
Total Current Tax Expense (Benefit)	0.1		0.5		(0.2)
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Tax Expense	22.9	[2]	37.0	[2]	27.4	[2]
Deferred State Tax Expense (Benefit)	6.5	[2]	1.4	[2]	9.3	[2]
Investment Tax Credit Amortization	(0.8)		(0.9)		(0.9)
Total Deferred Tax Expense	28.6		37.5		35.8
Total Income Tax Expense	$ 28.7		$ 38.0		$ 35.6

[1] For the years ended December 31, 2013, 2012 and 2011, the federal and state current tax expense (benefit) was due to NOLs which resulted primarily from the bonus depreciation provision of the Tax Relief, Unemployment Insurance Reauthorization, and Job Creation Act of 2010, and the American Taxpayer Relief Act of 2012. The federal and state NOLs will be carried forward to offset future taxable income.

[2] For the year ended December 31, 2013, federal deferred tax expense is lower than the prior year primarily due to higher renewable tax credits. For the years ended December 31, 2013, 2012, and 2011, state deferred tax expense includes state renewable tax credits earned, net of valuation allowance, which will be carried forward to offset future state income taxes. The year ended December 31, 2011, included an income tax benefit for the reversal of a $6.2 million deferred tax liability related to a revenue receivable that Minnesota Power agreed to forgo as part of a stipulation and settlement agreement in its 2010 rate case and a benefit of $2.9 million related to the MPUC approval of our request to defer the retail portion of the tax charge taken in 2010 as a result of the PPACA.