BENEFITS Benefits - Narrative (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended					12 Months Ended				12 Months Ended			9 Months Ended	3 Months Ended	12 Months Ended		9 Months Ended	3 Months Ended	12 Months Ended		9 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Supplemental Employee Retirement Plans, Defined Benefit	Dec. 31, 2012 Savings Plan	Dec. 31, 2012 Pension Plans, Defined Benefit	Dec. 31, 2011 Pension Plans, Defined Benefit	Dec. 31, 2012 Other Postretirement Benefit Plans, Defined Benefit	Dec. 31, 2012 Successor Other Postretirement Benefit Plans, Defined Benefit	Mar. 25, 2012 Predecessor Other Postretirement Benefit Plans, Defined Benefit	Dec. 31, 2011 Predecessor Other Postretirement Benefit Plans, Defined Benefit	Dec. 31, 2012 Equity Securities Pension Plans, Defined Benefit	Dec. 31, 2012 Fixed Income Securities Pension Plans, Defined Benefit	Dec. 31, 2012 Supplemental Employee Retirement Plans, Defined Benefit Missouri Gas Energy	Dec. 31, 2012 Supplemental Employee Retirement Plans, Defined Benefit Successor	Mar. 25, 2012 Supplemental Employee Retirement Plans, Defined Benefit Predecessor	Dec. 31, 2011 Supplemental Employee Retirement Plans, Defined Benefit Predecessor	Dec. 31, 2010 Supplemental Employee Retirement Plans, Defined Benefit Predecessor	Dec. 31, 2012 Savings Plan Successor	Mar. 25, 2012 Savings Plan Predecessor	Dec. 31, 2011 Savings Plan Predecessor	Dec. 31, 2010 Savings Plan Predecessor	Dec. 31, 2012 Pension Plans, Defined Benefit Successor	Mar. 25, 2012 Pension Plans, Defined Benefit Predecessor	Dec. 31, 2011 Pension Plans, Defined Benefit Predecessor
Defined Benefit Plan Disclosure
Defined Contribution Plan Employers Matching Contribution Percentage to Participants Percentage Conribution	100.00%
Large Cap US Equitiies					19.00%	17.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum										25.00%	65.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum										35.00%	75.00%
Pretax curtailment gain	$ 70
Noncurrent refund liability	59
Curtailment recognition (1)	11																				(75)	0	0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Arising During Period, before Tax						1
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate							3.51%	4.24%	4.26%
Defined Benefit Plan, Target Allocation Percentage, Cash Maximum				10.00%
Small Cap US Equities					2.00%	3.00%
International Equities					10.00%	10.00%
Fixed Income Securities					55.00%	53.00%
Cash Fund Investments					8.00%	10.00%
Other Investments - Plan Asset Allocation					6.00%	7.00%
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year				8		8
Defined Contribution Plan, Employer Matching Contribution, Percent	5.00%
Company Contributions Vested		100.00%	100.00%
Company Contributions Years			five									five
Defined Contribution Plan, Cost Recognized													$ 2	$ 1	$ 6	$ 5	$ 3	$ 1	$ 5	$ 5