Regulatory Matters (Details Textuals) (USD $)	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended		9 Months Ended	12 Months Ended		48 Months Ended
	Mar. 31, 2011	Jun. 30, 2011 percent	Sep. 30, 2011 MCF kWh years percent months	Dec. 31, 2011 years MCF months	Dec. 31, 2010	Sep. 30, 2011 Electric Utility [Member]	Dec. 31, 2011 Electric Utility [Member]	Dec. 31, 2011 Gas Utility [Member]	Dec. 31, 2015 Gas Utility [Member]
Regulatory Asset and Liability [Line Items]
Time Period Required by Non-Bypassable Securitization Bond Surcharge to Recover Securitized Regulatory Asset				14
Deferral of Investigation and Remediation of Costs Associated with Gas Utilities Former MGP Sites				10
Amortization Period of Cost to Achieve Deferral				10
MPSC Approved Annual Rate Increase			$ 175,000,000
MPSC Approved Return on Equity			10.50%
Expected Permanent Capital Structure Equity Percent			49.00%
Expected Permanent Capital Structure Debt Percent			51.00%
Self Implemented Rate Increase		107,000,000
Amount of Credit to CIM Regulatory Asset			37,000,000
Revised Annual Rate Increase				188,000,000
Annual Revenue Decoupling Mechanism Collar on Surcharge and Refund Year 1			1.50%
Annual Revenue Decoupling Mechanism Collar on Surcharge and Refund Year 2 and Subsequent Years			3.00%
To Reduce Nuclear Decommisssioning Surcharge Annually			20,000,000
Current Composite Depreciation Rate		3.33%
New Composite Depreciation Rates		3.06%
Additional Revenue for Renewable Energy Plan		100,000,000
Period to Implement Electric Utilities Renewable Energy Plan				20
Energy Optimization Overrecovery Electric Utility	21,000,000
Energy Optimization Overrecovery Gas Utility	5,600,000
Requested Recovery of Enery Optimization Expenses for Future Period						294,000,000			103,000,000
Proposed Refund of Restoration and Line Clearance Expense		16,000,000
Requested Recovery of Restoration Expenses	19,500,000
MPSC Authorized Surcharges to Recover Restoration Expenses			19,500,000
Period to Recover Surcharges for RETM and LCT			3
Requested net recovery of RETM and LCT			44,000,000
Requested Authority to Refund Revenue Decoupling Mechanism		56,000,000
RDM Refund Range Minimum First Pilot				56,000,000
RDM Refund Range Maximum First Pilot				140,000,000
Possible Refund Calculations for Revenue Decoupling Mechanism Maximum			71,000,000
RDM Refund Range Minimum Second Pilot				10,000,000
RDM Refund Range Maximum Second Pilot				130,000,000
Requesting Authority to Refund Uncollectible Expense to Customers	7,000,000
MPSC Authorized Refund to Customer Bills			7,000,000
Requested Recovery of Electric Utility Choice Incentive Mechanism					105,000,000
Approved Recovery of Electric Utility Choice Incentive Mechanism				105,000,000
Period to Apply Approved Electric Utility Choice Icentive Mechanism Surcharges				12
Requested Recovery Net of the Self Implementation Credit Applied per MPSC Order			73,000,000
Net Under Recovery of Power Suppy Cost Recovery Expense	52,600,000
Net Over Recovery of Power Supply Cost Recovery Expense			15,600,000
Under Recovery for the Pension Equalization Mechanism			7,100,000
Overy Recovery on Refund for Self Implemented Rates			3,800,000
Power Supply Cost Recovery Plan Case Factor Current Year			2.98
Power Supply Cost Recovery Expense Forecast For Current Year			1,200,000,000
Power Supply Cost Recovery Under Collection One Year Prior			36,000,000
Power Supply cost Recovery Plan Case Factor Next Year			4.18
Power Supply Cost Recovery Expense Forecast Next Year			1,400,000,000
Projected Power Supply Cost Recovery Under Recovery for Current Year			158,000,000
Escrowed LIEEF Amounts							23,000,000	3,000,000
Vulnerable household warmth fund amount to be collected				48,000,000
MPSC Authorized Recovery of Uncollectibe Expense	31,000,000
Uncollectibe Expense Prior Year			7,000,000
Uncollectible Expense Tracking Mechanism Under Collection Three Years Prior			24,000,000
Requested Recovery for Revenue Decoupling Mechanism			20,000,000
Period of Gas Cost Recovery Reconciliation				12
Disallowed Recovery Related fo the Pricing of Certain Gas Purchases				3,000,000
Gas Cost Reconciliation Over Recovery				9,000,000
GCR Plan Case Factor Current Year and Next Year			5.89
GCR Plan Case Factor Next Year and Following Year				5
Gas Main Renewal Program Implentation Time Period			10
Gas Main Renewal Program Capital Expenditures			17,000,000
Gas Meter Move Out Program Implementation Time Period			10
Gas Meter Move Out Program Capital Expenditures			$ 22,000,000