Regulatory Matters (Details Textuals) (USD $)	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2012 years	Mar. 31, 2011	Sep. 30, 2011	Dec. 31, 2011
Regulatory Asset and Liability [Line Items]
Accrued Liabilities for RDM Refunds Relating to 2010	$ 56,000,000
Accrued Liabilities for RDM Refunds Relating to 2011	71,000,000
Approved Rate Base Relating to the AMI Program	37,000,000
Expenditures Net of Grant Funds for AMI Program	83,000,000
Matching Grant Funds for the AMI Program	53,000,000
RDM Refund Range Minimum First Pilot	56,000,000
RDM Refund Range Maximum First Pilot	140,000,000
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		9,000,000
Renewable Energy Plan Capital Expenditures Deferred to Future Rate Cases	3,000,000
PSCR Reconciliation Calculating net Under Recovery	148,000,000
Net Under Recovery of Power Suppy Cost Recovery Expense		52,600,000
PSCR Reconciliation Includes an Over-Recovery	3,800,000
Net Over Recovery of Power Supply Cost Recovery Expense			10,500,000
Vulnerable Household Warmth Fund Amount to be Collected				48,000,000
Filed a Rate Case with the MPSC Requesting an Increase in Revenue	77,000,000
Time Period to Implement Requested Revenue Increase	5
Gas Cost Recovery Plan Case Factor Current Year Approved	5.89
UETM Requesting Authority to Refund	7,000,000
Refund Consists of an Over-Recovery	19,000,000
Refund Consists of an Under-Recovery	12,000,000
Electric Utility [Member]
Regulatory Asset and Liability [Line Items]
Requested Recovery of Energy Optimization Expenses for Future Period			294,000,000
Escrowed LIEEF Amounts				22,000,000
Gas Utility [Member]
Regulatory Asset and Liability [Line Items]
Requested Recovery of Energy Optimization Expenses for Future Period			103,000,000
Escrowed LIEEF Amounts				$ 3,000,000