Regulatory Matters (Details Textuals) (USD $)	12 Months Ended	0 Months Ended	3 Months Ended
	Dec. 31, 2014	Dec. 19, 2014	Mar. 31, 2013	Dec. 31, 2013	Sep. 30, 2014	Jul. 30, 2012	Jan. 01, 2014	Sep. 30, 2012	Sep. 26, 2014	Aug. 31, 2013	Nov. 30, 2014
Regulatory Assets [Line Items]
Time period required by non-bypassable securitization bond surcharge to recover securitized regulatory asset	14 years
Amortization period of cost to achieve deferral	10 years
Deferral of investigation and remediation of costs associated with gas utilities former MGP sites	10 years
Regulatory liabilities	$ 820,000,000			$ 1,164,000,000
Refundable Revenue Decoupling [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	67,000,000			127,000,000
Electric [Member]
Regulatory Assets [Line Items]
Fermi 2 production level of full capacity						68.00%
Maximum of challenged Fermi 2 outage charges					32,000,000
Electric [Member] | Refundable Revenue Decoupling [Member]
Regulatory Assets [Line Items]
Regulatory liabilities								127,000,000
Monthly amount to amortize from liability to income							10,600,000
MPSC [Member] | Electric [Member]
Regulatory Assets [Line Items]
Public utilities, requested rate increase (decrease)		370,000,000
Rate increase previously authorized by the MPSC challenged by Court of Appeals reopened by the MPSC										11,000,000
Approved recovery amount for customer 360									215,000,000
Approved amortization period for customer 360 recovery	15 years
PSCR under-recovery from 2 plan years prior			87,000,000
PSCR under-recovery from 3 plan years prior			148,000,000
MPSC [Member] | Gas [Member]
Regulatory Assets [Line Items]
Infrastructure recovery mechanism surcharge											$ 47,000,000