Illinois Power Generating 10-Q 12 Nov 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014	Nov. 03, 2014
Entity Information [Line Items]	'	'
Entity Registrant Name	'ILLINOIS POWER GENERATING COMPANY	'
Entity Central Index Key	'0001135361	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Non-accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	30-Sep-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q3	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	2,000

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets	'	'
Cash and cash equivalents	$186	$190
Accounts receivable, affiliates	51	59
Accounts receivable	14	18
Inventory	69	78
Prepayments and other current assets	10	18
Total Current Assets	330	363
Property, Plant and Equipment	2,937	2,900
Accumulated depreciation	-1,098	-1,027
Property, Plant and Equipment, Net	1,839	1,873
Other Assets	34	28
Total Assets	2,203	2,264
Current Liabilities	'	'
Accounts payable	34	38
Accounts payable, affiliates	6	0
Taxes accrued	9	12
Accrued interest	25	10
Current accumulated deferred income taxes, net	18	19
Accrued liabilities and other current liabilities	13	15
Total Current Liabilities	105	94
Long-term debt	824	824
Other Liabilities	'	'
Accumulated deferred income taxes, net	489	520
Asset retirement obligations	46	43
Other long-term liabilities	25	20
Total Liabilities	1,489	1,501
Commitments and Contingencies (Note 9)	'	'
Stockholder’s Equity	'	'
Common stock, no par value, 10,000 shares authorized – 2,000 shares outstanding	0	0
Additional paid-in capital	551	551
Retained earnings	-11	-11
Accumulated other comprehensive loss, net of tax	166	216
Total Illinois Power Generating Company Stockholder’s Equity	706	756
Noncontrolling interest	8	7
Total Equity	714	763
Total Liabilities and Equity	$2,203	$2,264

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]	'	'
Common stock, no par value	$0	$0
Common stock, shares authorized	10,000	10,000
Common stock, shares outstanding	2,000	2,000

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]	'	'	'	'
Revenues	$165	$278	$483	$653
Cost of sales, excluding depreciation expense	-121	-229	-340	-499
Gross margin	44	49	143	154
Operating and maintenance expense	-37	-36	-120	-126
Impairment and other charges	0	5	0	-197
Depreciation expense	-25	-18	-73	-60
Other income and expense, net	0	1	0	1
Operating income (loss)	-18	1	-50	-228
Interest expense	-10	-10	-30	-31
Loss before income taxes	-28	-9	-80	-259
Income tax benefit	11	4	32	103
Net loss	-17	-5	-48	-156
Less: Net income attributable to noncontrolling interest	0	0	2	0
Net loss attributable to Illinois Power Generating Company	($17)	($5)	($50)	($156)

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Loss) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'	'		'
Net loss	($17)	($5)	($48)		($156)
Other comprehensive loss before reclassifications:	'	'	'		'
Actuarial loss due to pension plan remeasurement (net of tax benefit of zero, zero, $1 million and zero, respectively)	0	0	-2		0
Amounts reclassified from accumulated other comprehensive loss:	'	'	'		'
Reclassification of mark-to-market losses to earnings on interest rate swaps designated as cash flow hedges (net of tax benefit of zero, zero, zero and zero, respectively)	1	1	1	[1]	1	[1]
Settlement loss on pension plan (net of tax benefit of zero, zero, zero and zero, respectively)	0	0	2		0
Amortization of unrecognized prior service credit and actuarial loss (net of tax benefit of zero, zero, zero and $1 million, respectively)	-1	0	-1	[2]	2	[2]
Other comprehensive income, net of tax	0	1	0		3
Comprehensive loss	-17	-4	-48		-153
Less: Comprehensive income attributable to noncontrolling interest	0	0	2		0
Total comprehensive loss attributable to Illinois Power Generating Company	($17)	($4)	($50)		($153)
[1]	Amount related to the reclassification of mark-to-market losses on cash flow hedging activities and was recorded in Interest expense on our unaudited consolidated statements of operations. Please read Note 4—Risk Management, Derivatives and Financial Instruments for further discussion.
[2]	Amounts are associated with our defined benefit pension and other post-employment benefit plans and are included in the computation of net periodic benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Statement of Comprehensive Income [Abstract]	'	'	'		'
Tax on actuarial loss due to pension plan remeasurement	$0	$0	$1		$0
Tax on reclassification of mark-to-market losses to earnings on interest rate swaps designated as cash flow hedges	0	0	0	[1]	0	[1]
Tax on pension plan settlement loss	0	0	0	[2]	0	[2]
Tax on amortization of unrecognized prior service credit and actuarial loss	$0	$0	$0		$1
[1]	Amount related to the reclassification of mark-to-market losses on cash flow hedging activities and was recorded in Interest expense on our unaudited consolidated statements of operations. Please read Note 4—Risk Management, Derivatives and Financial Instruments for further discussion.
[2]	Amount related to the settlement loss on the EEI pension plan and is included in the computation of total benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
CASH FLOWS FROM OPERATING ACTIVITIES:	'	'
Net loss	($48)	($156)
Adjustments to reconcile net loss to net cash flows from operating activities:	'	'
Loss on asset impairment	0	197
Depreciation expense	73	60
Deferred income taxes and investment tax credits, net	-32	-35
Other	4	-2
Changes in working capital:	'	'
Accounts receivable, net	12	9
Inventory	5	23
Prepayments and other current assets	8	-2
Accounts payable and accrued liabilities	11	-9
Other	-1	-7
Net cash provided by operating activities	32	78
CASH FLOWS FROM INVESTING ACTIVITIES:	'	'
Capital expenditures	-36	-40
Proceeds from asset sales, net	0	101
Money pool advances, net	0	-139
Net cash used in investing activities	-36	-78
CASH FLOWS FROM FINANCING ACTIVITIES:	'	'
Net cash provided by financing activities	0	0
Net decrease in cash and cash equivalents	-4	0
Cash and cash equivalents, beginning of year	190	25
Cash and cash equivalents, end of period	$186	$25

Basis_of_Presentation_and_Orga

Basis of Presentation and Organization	9 Months Ended
	Sep. 30, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Basis of Presentation and Organization	'
	Note 1—Basis of Presentation and Organization
	The accompanying unaudited consolidated financial statements have been prepared in accordance with the instructions to interim financial reporting as prescribed by the SEC. The year-end consolidated balance sheet data was derived from audited consolidated financial statements but does not include all disclosures required by GAAP.  The unaudited consolidated financial statements contained in this report include all material adjustments of a normal recurring nature that, in the opinion of management, are necessary for a fair presentation of the results for the interim periods. Certain prior period amounts in our consolidated statements of operations have been reclassified to conform to current year presentation. These interim financial statements should be read together with the consolidated financial statements and notes thereto included in our annual report on Form 10-K for the year ended December 31, 2013, filed with the SEC on March 28, 2014, which we refer to as our “Form 10-K.” Unless the context indicates otherwise, throughout this report, the terms “Genco,” “the Company,” “we,” “us,” “our,” and “ours” are used to refer to Illinois Power Generating Company and its direct and indirect subsidiaries.
	We are an electric generation subsidiary of Illinois Power Resources, LLC (“IPR”), which is an indirect wholly-owned subsidiary of Dynegy Inc. (“Dynegy”). We are headquartered in Houston, Texas and were incorporated in Illinois in March 2000. We own and operate a merchant generation business in Illinois and have an 80 percent ownership interest in Electric Energy, Inc. (“EEI”). EEI operates merchant electric generation facilities and FERC-regulated transmission facilities in Illinois and Kentucky. We also consolidate our wholly-owned subsidiary, Coffeen and Western Railroad Company, for financial reporting purposes. All significant intercompany transactions have been eliminated.
	On December 2, 2013 (the “Acquisition Date”), we were acquired indirectly by Illinois Power Holdings, LLC (“IPH”), an indirect wholly-owned subsidiary of Dynegy. On the Acquisition Date, pursuant to the terms of the definitive agreement dated as of March 14, 2013 and as amended on the Acquisition Date (the “AER Transaction Agreement”) by and between IPH and Ameren Corporation (“Ameren”), IPH completed its acquisition from Ameren of 100 percent of the equity interests of New Ameren Energy Resources, LLC (“New AER”) and its subsidiaries (the “AER Acquisition”).  “Push-down accounting” was not applied as a result of the AER Acquisition, which would require the adjustment of the assets and liabilities to fair value recognized by Dynegy to be shown in our consolidated financial statements.
	IPH and its direct and indirect subsidiaries, including Genco, are organized into ring-fenced groups to maintain corporate separateness from Dynegy and its other subsidiaries, for the purpose of minimizing risk of claims against Dynegy for IPH’s and our obligations. We have an independent director whose consent is required for certain corporate actions, including material transactions with affiliates. We maintain separate books, records and bank accounts and separately appoint officers.  Furthermore, we pay liabilities from our own funds, conduct business in our own name and have restrictions on pledging our assets for the benefit of certain other persons.

Accounting_Policies

Accounting Policies	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Accounting Policies	'
	Note 2—Accounting Policies
	The accounting policies followed by the Company are set forth in Note 1—Summary of Significant Accounting Policies of the Notes to Consolidated Financial Statements in our Form 10-K. There have been no significant changes to these policies during the nine months ended September 30, 2014.
	The preparation of consolidated financial statements in conformity with GAAP requires management to make informed estimates and judgments that affect our reported financial position and results of operations based on currently available information.  Actual results could differ materially from our estimates. The results of operations for the interim periods presented in this Form 10-Q are not necessarily indicative of the results to be expected for the full year or any other interim period due to seasonal fluctuations in demand for our energy products and services, changes in commodity prices, timing of maintenance and other expenditures and other factors.
	Accounting Standards Adopted During the Current Period
	Presentation of Unrecognized Tax Benefits. In July 2013, the FASB issued ASU 2013-11-Income Taxes (Topic 740): Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. The provisions of the rule require an unrecognized tax benefit to be presented as a reduction to a deferred tax asset in the financial statements for an NOL carryforward, a similar tax loss, or a tax credit carryforward except in circumstances when the carryforward or tax loss is not available at the reporting date under the tax laws of the applicable jurisdiction to settle any additional income taxes or the tax law does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purposes. When those circumstances exist, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. The new financial statement presentation provisions relating to this ASU are prospective and effective for interim and annual periods beginning after December 15, 2013. The adoption of this ASU did not have a material impact on our consolidated financial statements.
	Accounting Standards Not Yet Adopted
	Reporting Discontinued Operations and Asset Disposals. In April 2014, the FASB issued ASU 2014-08-Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosure of Disposals of Components of an Entity. The amendments in this ASU change the requirements for reporting discontinued operations in Subtopic 205-20. An entity is required to report within discontinued operations on the statement of operations the results of a component or group of components of an entity if the disposal represents a strategic shift that has, or will have, a major effect on an entity’s operations and financial results. Additionally, the associated assets and liabilities are required to be presented separately from other assets and liabilities on the balance sheet for all comparative periods. The ASU includes updated guidance regarding what meets the definition of a component of an entity. The new financial statement presentation provisions relating to this ASU are prospective and effective for interim and annual periods beginning after December 15, 2014, with early adoption permitted. We do not anticipate the adoption of this ASU having a material impact on our consolidated financial statements.
	Revenue from Contracts with Customers. In May 2014, the FASB and IASB jointly issued ASU 2014-09-Revenue from Contracts with Customers (Topic 606). The amendments in this ASU develop a common revenue standard for U.S. GAAP and IFRS by removing inconsistencies and weaknesses in revenue requirements, providing a more robust framework for addressing revenue issues, improving comparability of revenue recognition practices, providing more useful information to users of financial statements and simplifying the preparation of financial statements. The guidance in this ASU is effective for interim and annual periods beginning after December 15, 2016. We are currently assessing this ASU; however, we do not anticipate the adoption of this ASU having a material impact on our consolidated financial statements.

Asset_Sales

Asset Sales	9 Months Ended
	Sep. 30, 2014
Property, Plant and Equipment Impairment or Disposal [Abstract]	'
Asset Sales	'
	Note 3—Asset Sales
	In October 2013, we divested our Elgin, Gibson City and Grand Tower gas-fired facilities (the “Gas-Fired Facilities”) to Ameren Energy Medina Valley Cogen L.L.C. (“Medina Valley”), an affiliate of Ameren Energy Resources Company, LLC (“AER”) that IPH did not acquire in the AER Acquisition, under a put option agreement that was assumed by Medina Valley and exercised by us in March 2013 (the “Put Option”). As a result of our exercise of the Put Option, the Gas-Fired Facilities qualified for held for sale accounting and we recorded a pretax charge to earnings of $207 million during the three months ended March 31, 2013 to reflect the impairment of the Gas-Fired Facilities as the carrying value of the facilities exceeded their fair value. Fair value was based on the purchase agreement with Medina Valley. The impairment charge decreased by $5 million during the three months ended June 30, 2013, as the carrying value of the Gas-Fired Facilities decreased primarily as a result of derivative market value losses. The impairment charge decreased by an additional $5 million during the three months ended September 30, 2013, primarily as a result of the increase in the fair value of the disposal group based on the average of the three independent appraisers’ valuation of the Gas-Fired Facilities. As a result, we recorded a cumulative pretax charge to earnings of $197 million during the nine months ended September 30, 2013 to reflect the impairment of the Gas-Fired Facilities.

Risk_Management_Derivatives_an

Risk Management, Derivatives and Financial Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Instrument Detail [Abstract]	'
Risk Management, Derivatives and Financial Instruments	'
	Note 4—Risk Management, Derivatives and Financial Instruments
	Derivatives on the Balance Sheet. We did not have a material amount of derivative instruments as of September 30, 2014 and December 31, 2013.
	Impact of Derivatives on the Consolidated Statements of Operations
	The cumulative amount of pretax net losses on interest rate derivative instruments in AOCI was $5 million and $6 million as of September 30, 2014 and December 31, 2013, respectively. These interest rate swaps were executed in 2007 as a partial hedge of interest rate risks associated with our April 2008 debt issuance. The loss on the interest rate swaps is being amortized over a 10-year period that began in April 2008, $1.4 million of which will be amortized through 2014.
	Financial Instruments Not Designated as Hedges. In 2014 and 2013, we elected not to designate derivatives related to our power generation business and interest rate instruments as cash flow or fair value hedges.  Thus, we account for changes in the fair value of these derivatives within the consolidated statements of operations (herein referred to as “mark-to-market” accounting treatment).
	There was no material impact of mark-to-market gains (losses) on our unaudited consolidated statements of operations for the three and nine months ended September 30, 2014. Revenues on our unaudited consolidated statements of operations for the three and nine months ended September 30, 2013 include mark-to-market gains of $1 million and $3 million, respectively, related to our commodity derivatives.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Note 5—Fair Value Measurements
	We apply the market approach for recurring fair value measurements, employing valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs.  We have consistently used this valuation technique for all periods presented.  Please read Note 9—Fair Value Measurements in our Form 10-K for further discussion and definitions of the fair value hierarchy.
	We did not have material amounts of outstanding derivative positions as of September 30, 2014 and December 31, 2013.
	Fair Value of Financial Instruments.  We have determined the estimated fair value amounts using available market information and selected valuation methodologies.  Considerable judgment is required in interpreting market data to develop the estimates of fair value.  The use of different market assumptions or valuation methodologies could have a material effect on the estimated fair value amounts.
	The carrying values of financial assets and liabilities (cash and cash equivalents, accounts receivable, restricted cash and accounts payable) not presented in the table below approximate fair values due to the short-term maturities of these instruments.  Unless otherwise noted, the fair value of debt as reflected in the table has been calculated based on the average of certain available broker quotes as of September 30, 2014 and December 31, 2013, respectively. All fair values presented below are classified within Level 2 of the fair value hierarchy.
			September 30, 2014				December 31, 2013
	(amounts in millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	7.95% Senior Notes Series F, due 2032 (1)		$	274	$	274	$	274	$	216
	7.00% Senior Notes Series H, due 2018		$	300	$	287	$	300	$	252
	6.30% Senior Notes Series I, due 2020		$	250	$	235	$	250	$	196
	__________________________________________
	-1	Carrying amount includes unamortized discount of $1 million as of September 30, 2014 and December 31, 2013. Please read Note 8—Debt for further discussion.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Accumulated Other Comprehensive Income (Loss)	'
	Note 6—Accumulated Other Comprehensive Income (Loss)
	Changes in accumulated other comprehensive income (loss), net of tax, by component are as follows:
			Nine Months Ended September 30,
	(amounts in millions)		2014			2013
	Beginning of period		$	(11	)	$	(40	)
	Other comprehensive loss before reclassifications:
	Actuarial loss due to pension plan remeasurement (net of tax benefit of $1 million and zero, respectively)		(2		)	—
	Amounts reclassified from accumulated other comprehensive loss:
	Reclassification of mark-to-market losses to earnings on interest rate swaps designated as cash flow hedges (net of tax benefit of zero and zero, respectively) (1)		1			1
	Settlement loss on pension plan (net of tax benefit of zero and zero, respectively) (2)		2			—
	Amortization of unrecognized prior service credit and actuarial loss (net of tax benefit of zero and $1 million, respectively) (3)		(1		)	2
	Net current period other comprehensive income, net of tax		—			3
	End of period		$	(11	)	$	(37	)
	_______________________________________
	-1	Amount related to the reclassification of mark-to-market losses on cash flow hedging activities and was recorded in Interest expense on our unaudited consolidated statements of operations. Please read Note 4—Risk Management, Derivatives and Financial Instruments for further discussion.
	-2	Amount related to the settlement loss on the EEI pension plan and is included in the computation of total benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.
	-3	Amounts are associated with our defined benefit pension and other post-employment benefit plans and are included in the computation of net periodic benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.

Inventory

Inventory	9 Months Ended
	Sep. 30, 2014
Inventory Disclosure [Abstract]	'
Inventory	'
	Note 7—Inventory
	A summary of our inventories is as follows:
	(amounts in millions)	September 30, 2014		31-Dec-13
	Materials and supplies	$	30	$	33
	Coal	37		43
	Fuel oil	2		2
	Total	$	69	$	78

Debt

Debt	9 Months Ended
	Sep. 30, 2014
Long-term Debt, Unclassified [Abstract]	'
Debt	'
	Note 8—Debt
	A summary of our long-term debt is as follows:
	(amounts in millions)		September 30, 2014			December 31, 2013
	Unsecured notes:
	7.95% Senior Notes Series F, due 2032		$	275		$	275
	7.00% Senior Notes Series H, due 2018		300			300
	6.30% Senior Notes Series I, due 2020		250			250
			825			825
	Unamortized discount		(1		)	(1		)
	Total Long-term debt		$	824		$	824
	Indenture Provisions and Other Covenants
	At September 30, 2014, we were in compliance with the provisions and covenants contained within our indenture. Our indenture includes provisions that require us to maintain certain interest coverage and debt-to-capital ratios in order for us to pay dividends, to make principal or interest payments on subordinated borrowings, to make loans to or investments in affiliates or to incur additional external, third-party indebtedness. The following table summarizes these required ratios as of September 30, 2014:
			Required Ratio
	Restricted payment interest coverage ratio (1)		≥1.75
	Additional indebtedness interest coverage ratio (2)		≥2.50
	Additional indebtedness debt-to-capital ratio (2)		≤60%
	_______________________________________
	-1	As of the date of a restricted payment, as defined, the minimum ratio must have been achieved for the most recently ended four fiscal quarters and projected by management to be achieved for each of the subsequent four six-month periods.
	-2	Ratios must be computed on a pro forma basis considering the additional indebtedness to be incurred and the related interest expense. Other borrowings from third-party external sources are included in the definition of indebtedness and are subject to these incurrence tests.
	Our debt incurrence-related ratio restrictions under the indenture may be disregarded if both Moody's and S&P reaffirm the ratings in place at the time of the debt incurrence after considering the additional indebtedness.
	Our indenture provides that dividends cannot be paid unless the actual interest coverage ratio for our most recently ended four fiscal quarters and the interest coverage ratios projected by management for each of the subsequent four six-month periods are greater than a specified minimum level. Based on September 30, 2014 calculations, our interest coverage ratios are less than the minimum ratios required to pay dividends and borrow additional funds from external, third-party sources. As a result, we were restricted from paying dividends as of September 30, 2014.
	In order for us to issue securities in the future, we will have to comply with all applicable indenture requirements in effect at the time of any such issuances.

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Note 9—Commitments and Contingencies
	Legal Proceedings
	Set forth below is a summary of our material ongoing legal proceedings. We record accruals for estimated losses from contingencies when available information indicates that a loss is probable and the amount of the loss, or range of loss, can be reasonably estimated.  In addition, we disclose matters for which management believes a material loss is reasonably possible.  In all instances, management has assessed the matters below based on current information and made judgments concerning their potential outcome, giving consideration to the nature of the claim, the amount, if any, and nature of damages sought and the probability of success.  Management regularly reviews all new information with respect to such contingency and adjusts its assessment and estimates of such contingencies accordingly.  Because litigation is subject to inherent uncertainties including unfavorable rulings or developments, it is possible that the ultimate resolution of our legal proceedings could involve amounts that are different from our currently recorded accruals and that such differences could be material.
	In addition to the matters discussed below, we are party to other routine proceedings arising in the ordinary course of business or related to discontinued business operations.  Any accruals or estimated losses related to these matters are not material. In management’s judgment, the ultimate resolution of these matters will not have a material effect on our financial condition, results of operations or cash flows.
	Variance. In January 2014, an environmental group filed a petition for review in the Illinois Fourth District Appellate Court of the IPCB’s November 2013 decision and order granting IPH a variance extending the applicable compliance dates for MPS SO2 emission limits. On January 17, 2014, IPH filed a Motion to Dismiss. On February 24, 2014, the Fourth District Appellate Court granted the motion and dismissed the appeal. On April 1, 2014, the environmental group filed a petition for leave to appeal the Appellate Court’s decision with the Illinois Supreme Court. On May 5, 2014, we filed an answer opposing review by the Illinois Supreme Court. On September 24, 2014, the Illinois Supreme Court denied the petition for leave to appeal.
	New Source Review and Clean Air Litigation
	Since 1999, the EPA has been engaged in a nationwide enforcement initiative to determine whether coal-fired power plants failed to comply with the requirements of the NSR and NSPS provisions under the CAA when the plants implemented modifications. The EPA’s initiative focuses on whether projects performed at power plants triggered various permitting requirements, including the need to install pollution control equipment.
	Commencing in 2005, we received a series of information requests from the EPA pursuant to Section 114(a) of the CAA. The requests sought detailed operating and maintenance history data with respect to our Coffeen, Newton and Joppa facilities. In August 2012, the EPA issued a Notice of Violation alleging that projects performed in 1997, 2006 and 2007 at our Newton facility violated PSD, Title V permitting and other requirements. We believe our defenses to the allegations described in the Notice of Violation are meritorious. A recent decision by the U.S. Court of Appeals for the Seventh Circuit held that similar claims older than five years were barred by the statute of limitations. If not overturned, this decision may provide an additional defense to the allegations in the Newton facility Notice of Violation. Ultimate resolution of these matters could have a material adverse impact on our future financial condition, results of operations and cash flows. A resolution could result in increased capital expenditures for the installation of pollution control equipment, increased operations and maintenance expenses, and penalties. At this time we are unable to make a reasonable estimate of the possible costs, or range of costs, that might be incurred to resolve these matters.
	Groundwater
	Hydrogeologic investigations of the CCR surface impoundments have been performed at our facilities.  Groundwater monitoring results indicate that the CCR surface impoundments at each of our facilities potentially impact onsite groundwater.
	In 2012, the Illinois EPA issued violation notices with respect to groundwater conditions at our Coffeen and Newton facilities’ CCR surface impoundments. In February 2013, the Illinois EPA provided written notice that it may pursue legal action with respect to each of these matters through referral to the Illinois Office of the Attorney General. In September 2014, the Illinois EPA issued a permit modification for the Newton facility’s active CCR landfill that requires us to perform assessment monitoring concerning previously reported groundwater quality standard exceedances and to submit the findings of that assessment, including proposed courses of action, in April 2015.
	In April 2013, AER filed a proposed rulemaking with the IPCB which, if approved, would provide for the systematic and eventual closure of our CCR surface impoundments. In October 2013, the Illinois EPA filed a proposed rulemaking with the IPCB that would establish processes governing monitoring, preventative response, corrective action and closure of CCR surface impoundments at all power generating facilities in Illinois. The AER rulemaking (now IPH) has been stayed to allow the Illinois EPA proposed rulemaking to proceed.
	At this time we cannot reasonably estimate the costs or range of costs of resolving the Newton and Coffeen groundwater matters, but resolution of these matters may cause us to incur significant costs that could have a material adverse effect on our financial condition, results of operations and cash flows. During the first quarter 2013, we revised our ARO fair value estimates relating to CCR surface impoundments.
	Guaranty Agreement
	In connection with the AER Acquisition, Genco has provided an uncapped Guaranty Agreement of certain obligations of IPH under the AER Transaction Agreement. Concurrently with the closing of the AER Transaction Agreement on the Acquisition Date, Genco entered into the Guaranty Agreement in favor of Ameren, pursuant to which Genco guaranteed certain of IPH’s credit support obligations and tax and environmental indemnification obligations under the AER Transaction Agreement.

Related_Party_Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Related Party Transactions	'
	Note 10—Related Party Transactions
	We have engaged in, and may in the future engage in, affiliate transactions in the normal course of business. These transactions primarily consist of power purchases and sales, services received or rendered, and borrowings and lendings. For a discussion of our material related party agreements, please read Note 2—Related Party Transactions of the Form 10-K.
	The following table summarizes the affiliate accounts receivable and payable on our unaudited consolidated balance sheets.
		September 30, 2014								December 31, 2013
	(amounts in millions)	Accounts Receivable, Affiliates				Accounts Payable, Affiliates				Accounts Receivable, Affiliates				Accounts Payable, Affiliates
	Power supply agreements	$	50			$	—			$	58			$	—
	Other	1				6				1				—
	Total	$	51			$	6			$	59			$	—
	The following table presents the impact of related party transactions on our unaudited consolidated statements of operations for the three and nine months ended September 30, 2014 and 2013. It is based primarily on the agreements discussed below and in Note 2—Related Party Transactions of the Form 10-K.
				Three Months Ended September 30,								Nine Months Ended September 30,
	(amounts in millions)	Income Statement Line Item		2014				2013				2014				2013
	Power supply agreements	Revenues		$	162			$	219			$	480			$	557
	Services provided to AER affiliates	Revenues		$	—			$	1			$	—			$	5
	Services agreement	Operating and maintenance expense		$	10			$	2			$	31			$	8
	EEI power supply agreement	Cost of sales		$	—			$	47			$	—			$	65
	Power Supply Agreements
	Genco has a PSA with Illinois Power Marketing Company (“IPM”), whereby Genco agreed to sell and IPM agreed to purchase all of the capacity and energy available from Genco’s generation fleet. IPM entered into a similar PSA with Illinois Power Resources Generating LLC (“IPRG”). Under the PSAs, revenues allocated between Genco and IPRG are based on reimbursable expenses and generation of each entity. Each PSA will continue through December 31, 2022, and from year to year thereafter. Either party to the respective PSA may elect to terminate the PSA by providing the other party with no less than six months advance written notice.
	EEI has a PSA with IPM, whereby EEI agreed to sell and IPM agreed to purchase all of the capacity and energy available from EEI’s generation fleet. The price that IPM pays for capacity is set annually based upon prevailing market prices. IPM pays spot market prices for the associated energy. In addition, EEI will at times purchase energy from IPM to fulfill obligations to a non-affiliated party. This PSA will continue through May 31, 2016. Subsequent to September 30, 2014, EEI executed an extension to the PSA agreement through December 31, 2022. There were no other changes to the terms and conditions.
	Collateral Agreement
	On February 26, 2014, Genco entered into a collateral agreement with IPM pursuant to which IPM may require Genco to provide collateral to IPM to secure obligations of IPM applicable to Genco’s assets. The initial collateral limit for Genco is $15 million and IPM can demand an additional $7.5 million for a total limit not to exceed $22.5 million. There have been no amounts provided under this agreement to date.
	Services Agreements
	Prior to the AER Acquisition, Ameren Services Company (“Ameren Services”), an Ameren subsidiary, provided support services to its affiliates, including us. The costs of services, including wages, employee benefits, professional services and other expenses, were based on, or were an allocation of, actual costs incurred. In addition, we provided affiliates, primarily Ameren Services, with access to our facilities for administrative purposes. The cost of the rent and facility services were based on, or were an allocation of, actual costs incurred.
	Upon the AER Acquisition, Dynegy and certain of its subsidiaries (collectively, the “Providers”) began providing certain services (the “Services”) to IPH, and certain of its consolidated subsidiaries (collectively, the “Recipients”), which includes us and EEI.
	The Providers act as agents for the Recipients for the limited purpose of providing the Services set forth in the service agreements. Prior to the beginning of each fiscal year in which Services are to be provided pursuant to the Service Agreements, the Providers and the Recipients agree on a budget for the Services, outlining, among other items, the contemplated scope of the Services to be provided in the following fiscal year and the cost of providing the Services. The Recipients will pay the Providers an annual management fee as agreed in the budget. We believe this is a reasonable method of allocating the costs of the Services to us and provides an appropriate reflection of the costs we would have incurred if we operated as an unaffiliated entity.
	Tax Sharing Agreement
	We are included in the consolidated tax returns of Dynegy. Under U.S. federal income tax law, Dynegy files consolidated income tax returns for itself and its subsidiaries. Dynegy is responsible for the federal tax liabilities of its subsidiaries which include the income and business activities of the ring-fenced entities and Dynegy’s other affiliates.  Genco and Dynegy have entered into a tax sharing agreement that also provides that we recognize taxes based on a separate company income tax return basis, as defined in the agreement.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Note 11—Income Taxes
	We compute our quarterly taxes under the effective tax rate method based on applying an anticipated annual effective rate to our year-to-date income or loss, except for significant unusual or extraordinary transactions.  Income taxes for significant unusual or extraordinary transactions are computed and recorded in the period that the specific transaction occurs.

Pension_and_Other_PostEmployme

Pension and Other Post-Employment Benefits Pension and Other Post-Employment Benefits	9 Months Ended
	Sep. 30, 2014
Postemployment Benefits [Abstract]	'
Pension and Other Post-Employment Benefits	'
	Note 12—Pension and Other Post-Employment Benefits
	We offer defined benefit pension and other post-employment benefit plans covering our employees. Separately, our EEI employees and retirees participate in EEI’s single-employer pension and other post-employment plans. We consolidate EEI; therefore, EEI’s plans are reflected in our pension and other post-employment balances and disclosures. Please read Note 6—Retirement Benefits in our Form 10-K for further discussion.
	Components of Net Periodic Benefit Cost.  The following table presents the components of our net periodic benefit cost of the EEI pension and other post-employment benefit plans for the three and nine months ended September 30, 2014 and 2013. Also reflected is an allocation of net periodic benefit costs from our participation in Dynegy’s single-employer pension and other post-employment plans for the three and nine months ended September 30, 2014 and Ameren’s single-employer pension and other post-employment plans for the three and nine months ended September 30, 2013.
		Pension Benefits						Other Benefits
		Three Months Ended September 30,
	(amounts in millions)	2014			2013			2014			2013
	Service cost benefits earned during the period	$	1		$	1		$	1		$	—
	Interest cost on projected benefit obligation	1			2			1			1
	Expected return on plan assets	(1		)	(3		)	(1		)	(1		)
	Amortization of:
	Prior service credit	—			—			(1		)	(2		)
	Actuarial loss	—			2			—			1
	Net periodic benefit cost (gain)	$	1		$	2		$	—		$	(1	)
		Pension Benefits						Other Benefits
		Nine Months Ended September 30,
	(amounts in millions)	2014			2013			2014			2013
	Service cost benefits earned during the period	$	2		$	3		$	1		$	1
	Interest cost on projected benefit obligation	3			7			2			3
	Expected return on plan assets	(3		)	(10		)	(3		)	(4		)
	Amortization of:
	Prior service credit	—			—			(3		)	(6		)
	Actuarial loss	—			6			2			3
	Net periodic benefit cost (gain)	2			6			(1		)	(3		)
	Settlements	2			—			—			—
	Total benefit cost (gain)	$	4		$	6		$	(1	)	$	(3	)
	In addition to the above net periodic benefit cost for pension and other post-employment plans, we were allocated approximately $1 million and $2 million in net periodic benefit costs for pension and other post-employment plans from Ameren Services employees doing work on our behalf during the three and nine months ended September 30, 2013, respectively.

Accounting_Policies_Policies

Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2014
Accounting Policies [Abstract]	'
Basis of Presentation	'
	The accompanying unaudited consolidated financial statements have been prepared in accordance with the instructions to interim financial reporting as prescribed by the SEC. The year-end consolidated balance sheet data was derived from audited consolidated financial statements but does not include all disclosures required by GAAP.  The unaudited consolidated financial statements contained in this report include all material adjustments of a normal recurring nature that, in the opinion of management, are necessary for a fair presentation of the results for the interim periods. Certain prior period amounts in our consolidated statements of operations have been reclassified to conform to current year presentation. These interim financial statements should be read together with the consolidated financial statements and notes thereto included in our annual report on Form 10-K for the year ended December 31, 2013, filed with the SEC on March 28, 2014, which we refer to as our “Form 10-K.” Unless the context indicates otherwise, throughout this report, the terms “Genco,” “the Company,” “we,” “us,” “our,” and “ours” are used to refer to Illinois Power Generating Company and its direct and indirect subsidiaries.
	We are an electric generation subsidiary of Illinois Power Resources, LLC (“IPR”), which is an indirect wholly-owned subsidiary of Dynegy Inc. (“Dynegy”). We are headquartered in Houston, Texas and were incorporated in Illinois in March 2000. We own and operate a merchant generation business in Illinois and have an 80 percent ownership interest in Electric Energy, Inc. (“EEI”). EEI operates merchant electric generation facilities and FERC-regulated transmission facilities in Illinois and Kentucky. We also consolidate our wholly-owned subsidiary, Coffeen and Western Railroad Company, for financial reporting purposes. All significant intercompany transactions have been eliminated.
	On December 2, 2013 (the “Acquisition Date”), we were acquired indirectly by Illinois Power Holdings, LLC (“IPH”), an indirect wholly-owned subsidiary of Dynegy. On the Acquisition Date, pursuant to the terms of the definitive agreement dated as of March 14, 2013 and as amended on the Acquisition Date (the “AER Transaction Agreement”) by and between IPH and Ameren Corporation (“Ameren”), IPH completed its acquisition from Ameren of 100 percent of the equity interests of New Ameren Energy Resources, LLC (“New AER”) and its subsidiaries (the “AER Acquisition”).  “Push-down accounting” was not applied as a result of the AER Acquisition, which would require the adjustment of the assets and liabilities to fair value recognized by Dynegy to be shown in our consolidated financial statements.
	IPH and its direct and indirect subsidiaries, including Genco, are organized into ring-fenced groups to maintain corporate separateness from Dynegy and its other subsidiaries, for the purpose of minimizing risk of claims against Dynegy for IPH’s and our obligations. We have an independent director whose consent is required for certain corporate actions, including material transactions with affiliates. We maintain separate books, records and bank accounts and separately appoint officers.  Furthermore, we pay liabilities from our own funds, conduct business in our own name and have restrictions on pledging our assets for the benefit of certain other persons.
Use of Estimates	'
	The preparation of consolidated financial statements in conformity with GAAP requires management to make informed estimates and judgments that affect our reported financial position and results of operations based on currently available information.  Actual results could differ materially from our estimates. The results of operations for the interim periods presented in this Form 10-Q are not necessarily indicative of the results to be expected for the full year or any other interim period due to seasonal fluctuations in demand for our energy products and services, changes in commodity prices, timing of maintenance and other expenditures and other factors.
Accounting Standards Adopted and Not Yet Adopted During the Current Period	'
	Accounting Standards Adopted During the Current Period
	Presentation of Unrecognized Tax Benefits. In July 2013, the FASB issued ASU 2013-11-Income Taxes (Topic 740): Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists. The provisions of the rule require an unrecognized tax benefit to be presented as a reduction to a deferred tax asset in the financial statements for an NOL carryforward, a similar tax loss, or a tax credit carryforward except in circumstances when the carryforward or tax loss is not available at the reporting date under the tax laws of the applicable jurisdiction to settle any additional income taxes or the tax law does not require the entity to use, and the entity does not intend to use, the deferred tax asset for such purposes. When those circumstances exist, the unrecognized tax benefit should be presented in the financial statements as a liability and should not be combined with deferred tax assets. The new financial statement presentation provisions relating to this ASU are prospective and effective for interim and annual periods beginning after December 15, 2013. The adoption of this ASU did not have a material impact on our consolidated financial statements.
	Accounting Standards Not Yet Adopted
	Reporting Discontinued Operations and Asset Disposals. In April 2014, the FASB issued ASU 2014-08-Presentation of Financial Statements (Topic 205) and Property, Plant, and Equipment (Topic 360): Reporting Discontinued Operations and Disclosure of Disposals of Components of an Entity. The amendments in this ASU change the requirements for reporting discontinued operations in Subtopic 205-20. An entity is required to report within discontinued operations on the statement of operations the results of a component or group of components of an entity if the disposal represents a strategic shift that has, or will have, a major effect on an entity’s operations and financial results. Additionally, the associated assets and liabilities are required to be presented separately from other assets and liabilities on the balance sheet for all comparative periods. The ASU includes updated guidance regarding what meets the definition of a component of an entity. The new financial statement presentation provisions relating to this ASU are prospective and effective for interim and annual periods beginning after December 15, 2014, with early adoption permitted. We do not anticipate the adoption of this ASU having a material impact on our consolidated financial statements.
	Revenue from Contracts with Customers. In May 2014, the FASB and IASB jointly issued ASU 2014-09-Revenue from Contracts with Customers (Topic 606). The amendments in this ASU develop a common revenue standard for U.S. GAAP and IFRS by removing inconsistencies and weaknesses in revenue requirements, providing a more robust framework for addressing revenue issues, improving comparability of revenue recognition practices, providing more useful information to users of financial statements and simplifying the preparation of financial statements. The guidance in this ASU is effective for interim and annual periods beginning after December 15, 2016. We are currently assessing this ASU; however, we do not anticipate the adoption of this ASU having a material impact on our consolidated financial statements.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Liabilities	'
	The carrying values of financial assets and liabilities (cash and cash equivalents, accounts receivable, restricted cash and accounts payable) not presented in the table below approximate fair values due to the short-term maturities of these instruments.  Unless otherwise noted, the fair value of debt as reflected in the table has been calculated based on the average of certain available broker quotes as of September 30, 2014 and December 31, 2013, respectively. All fair values presented below are classified within Level 2 of the fair value hierarchy.
			September 30, 2014				December 31, 2013
	(amounts in millions)		Carrying Amount		Fair Value		Carrying Amount		Fair Value
	7.95% Senior Notes Series F, due 2032 (1)		$	274	$	274	$	274	$	216
	7.00% Senior Notes Series H, due 2018		$	300	$	287	$	300	$	252
	6.30% Senior Notes Series I, due 2020		$	250	$	235	$	250	$	196
	__________________________________________
	-1	Carrying amount includes unamortized discount of $1 million as of September 30, 2014 and December 31, 2013. Please read Note 8—Debt for further discussion.

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]	'
Schedule of Accumulated Other Comprehensive Income (Loss)	'
	Changes in accumulated other comprehensive income (loss), net of tax, by component are as follows:
			Nine Months Ended September 30,
	(amounts in millions)		2014			2013
	Beginning of period		$	(11	)	$	(40	)
	Other comprehensive loss before reclassifications:
	Actuarial loss due to pension plan remeasurement (net of tax benefit of $1 million and zero, respectively)		(2		)	—
	Amounts reclassified from accumulated other comprehensive loss:
	Reclassification of mark-to-market losses to earnings on interest rate swaps designated as cash flow hedges (net of tax benefit of zero and zero, respectively) (1)		1			1
	Settlement loss on pension plan (net of tax benefit of zero and zero, respectively) (2)		2			—
	Amortization of unrecognized prior service credit and actuarial loss (net of tax benefit of zero and $1 million, respectively) (3)		(1		)	2
	Net current period other comprehensive income, net of tax		—			3
	End of period		$	(11	)	$	(37	)
	_______________________________________
	-1	Amount related to the reclassification of mark-to-market losses on cash flow hedging activities and was recorded in Interest expense on our unaudited consolidated statements of operations. Please read Note 4—Risk Management, Derivatives and Financial Instruments for further discussion.
	-2	Amount related to the settlement loss on the EEI pension plan and is included in the computation of total benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.
	-3	Amounts are associated with our defined benefit pension and other post-employment benefit plans and are included in the computation of net periodic benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.

Inventory_Tables

Inventory (Tables)	9 Months Ended
	Sep. 30, 2014
Inventory Disclosure [Abstract]	'
Schedule of Inventory, Current	'
	A summary of our inventories is as follows:
	(amounts in millions)	September 30, 2014		31-Dec-13
	Materials and supplies	$	30	$	33
	Coal	37		43
	Fuel oil	2		2
	Total	$	69	$	78

Debt_Tables

Debt (Tables)	9 Months Ended
	Sep. 30, 2014
Long-term Debt, Unclassified [Abstract]	'
Schedule of Long-term Debt Instruments	'
	A summary of our long-term debt is as follows:
	(amounts in millions)		September 30, 2014			December 31, 2013
	Unsecured notes:
	7.95% Senior Notes Series F, due 2032		$	275		$	275
	7.00% Senior Notes Series H, due 2018		300			300
	6.30% Senior Notes Series I, due 2020		250			250
			825			825
	Unamortized discount		(1		)	(1		)
	Total Long-term debt		$	824		$	824
Schedule of Required Ratios	'
	The following table summarizes these required ratios as of September 30, 2014:
			Required Ratio
	Restricted payment interest coverage ratio (1)		≥1.75
	Additional indebtedness interest coverage ratio (2)		≥2.50
	Additional indebtedness debt-to-capital ratio (2)		≤60%
	_______________________________________
	-1	As of the date of a restricted payment, as defined, the minimum ratio must have been achieved for the most recently ended four fiscal quarters and projected by management to be achieved for each of the subsequent four six-month periods.
	-2	Ratios must be computed on a pro forma basis considering the additional indebtedness to be incurred and the related interest expense. Other borrowings from third-party external sources are included in the definition of indebtedness and are subject to these incurrence tests.

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2014
Related Party Transactions [Abstract]	'
Schedule of Related Party Transactions	'
	The following table summarizes the affiliate accounts receivable and payable on our unaudited consolidated balance sheets.
		September 30, 2014								December 31, 2013
	(amounts in millions)	Accounts Receivable, Affiliates				Accounts Payable, Affiliates				Accounts Receivable, Affiliates				Accounts Payable, Affiliates
	Power supply agreements	$	50			$	—			$	58			$	—
	Other	1				6				1				—
	Total	$	51			$	6			$	59			$	—
	The following table presents the impact of related party transactions on our unaudited consolidated statements of operations for the three and nine months ended September 30, 2014 and 2013. It is based primarily on the agreements discussed below and in Note 2—Related Party Transactions of the Form 10-K.
				Three Months Ended September 30,								Nine Months Ended September 30,
	(amounts in millions)	Income Statement Line Item		2014				2013				2014				2013
	Power supply agreements	Revenues		$	162			$	219			$	480			$	557
	Services provided to AER affiliates	Revenues		$	—			$	1			$	—			$	5
	Services agreement	Operating and maintenance expense		$	10			$	2			$	31			$	8
	EEI power supply agreement	Cost of sales		$	—			$	47			$	—			$	65

Pension_and_Other_PostEmployme1

Pension and Other Post-Employment Benefits (Tables)	9 Months Ended
	Sep. 30, 2014
Postemployment Benefits [Abstract]	'
Schedule of Net Periodic Benefit Costs	'
	The following table presents the components of our net periodic benefit cost of the EEI pension and other post-employment benefit plans for the three and nine months ended September 30, 2014 and 2013. Also reflected is an allocation of net periodic benefit costs from our participation in Dynegy’s single-employer pension and other post-employment plans for the three and nine months ended September 30, 2014 and Ameren’s single-employer pension and other post-employment plans for the three and nine months ended September 30, 2013.
		Pension Benefits						Other Benefits
		Three Months Ended September 30,
	(amounts in millions)	2014			2013			2014			2013
	Service cost benefits earned during the period	$	1		$	1		$	1		$	—
	Interest cost on projected benefit obligation	1			2			1			1
	Expected return on plan assets	(1		)	(3		)	(1		)	(1		)
	Amortization of:
	Prior service credit	—			—			(1		)	(2		)
	Actuarial loss	—			2			—			1
	Net periodic benefit cost (gain)	$	1		$	2		$	—		$	(1	)
		Pension Benefits						Other Benefits
		Nine Months Ended September 30,
	(amounts in millions)	2014			2013			2014			2013
	Service cost benefits earned during the period	$	2		$	3		$	1		$	1
	Interest cost on projected benefit obligation	3			7			2			3
	Expected return on plan assets	(3		)	(10		)	(3		)	(4		)
	Amortization of:
	Prior service credit	—			—			(3		)	(6		)
	Actuarial loss	—			6			2			3
	Net periodic benefit cost (gain)	2			6			(1		)	(3		)
	Settlements	2			—			—			—
	Total benefit cost (gain)	$	4		$	6		$	(1	)	$	(3	)

Basis_of_Presentation_and_Orga1

Basis of Presentation and Organization Basis of Presentation and Organization (Details)	Dec. 02, 2013	Sep. 30, 2014
		Electric Energy, Inc
Schedule of Equity Method Investments [Line Items]	'	'
Noncontrolling Interest, Ownership Percentage by Parent	'	80.00%
Percentage of Voting Interests Acquired	100.00%	'

Asset_Sales_Narrative_Details

Asset Sales (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended			9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2013
					Put Option [Member]	Put Option [Member]	Put Option [Member]	Put Option [Member]
					Gas-Fired Facilities [Member]	Gas-Fired Facilities [Member]	Gas-Fired Facilities [Member]	Gas-Fired Facilities [Member]
Impaired Long-Lived Assets Held and Used [Line Items]	'	'	'	'	'	'	'	'
Asset impairment	$0	($5)	$0	$197	($5)	($5)	$207	$197

Risk_Management_Derivatives_an1

Risk Management, Derivatives and Financial Instruments (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Apr. 30, 2008	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013
	Not Designated as Hedging Instrument	Not Designated as Hedging Instrument	Not Designated as Hedging Instrument	Not Designated as Hedging Instrument	Interest Rate Derivatives	Interest Rate Derivatives	Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent	Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
							Interest Rate Derivatives	Interest Rate Derivatives
Derivative [Line Items]	'	'	'	'	'	'	'	'
Cumulative deferred pretax losses	'	'	'	'	'	'	$5	$6
Cash Flow Hedge Gain (Loss) Reclassified to Revenue, Amortization Period	'	'	'	'	'10 years	'	'	'
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	'	'	'	'	'	1.4	'	'
Derivative Instruments, Mark-to-Market Gain (Loss) Recognized in Income, Net	$0	$1	$0	$3	'	'	'	'

Fair_Value_Measurements_Schedu

Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt) (Details) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
7.95% Senior Notes Series F, due 2032 | Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Unamortized Discount	$1		$1
Unsecured Debt | 7.95% Senior Notes Series F, due 2032	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Interest Rate, Stated Percentage	7.95%		'
Unsecured Debt | 7.95% Senior Notes Series F, due 2032 | Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Fair Value Disclosure	274	[1]	274	[1]
Unsecured Debt | 7.95% Senior Notes Series F, due 2032 | Fair Value	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Fair Value Disclosure	274	[1]	216	[1]
Unsecured Debt | 7.00% Senior Notes Series H, due 2018	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Interest Rate, Stated Percentage	7.00%		'
Unsecured Debt | 7.00% Senior Notes Series H, due 2018 | Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Fair Value Disclosure	300		300
Unsecured Debt | 7.00% Senior Notes Series H, due 2018 | Fair Value	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Fair Value Disclosure	287		252
Unsecured Debt | 6.30% Senior Notes Series I, due 2020	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Interest Rate, Stated Percentage	6.30%		'
Unsecured Debt | 6.30% Senior Notes Series I, due 2020 | Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Fair Value Disclosure	250		250
Unsecured Debt | 6.30% Senior Notes Series I, due 2020 | Fair Value	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Debt Instrument, Fair Value Disclosure	$235		$196
[1]	Carrying amount includes unamortized discount of $1 million as of September 30, 2014 and December 31, 2013. Please read Note 8—Debt for further discussion.

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]	'	'	'		'
Beginning of period	'	'	($11)		($40)
Other comprehensive loss before reclassifications:	'	'	'		'
Actuarial loss due to pension plan remeasurement (net of tax benefit of zero, zero, $1 million and zero, respectively)	0	0	-2		0
Amounts reclassified from accumulated other comprehensive loss:	'	'	'		'
Reclassification of mark-to-market losses to earnings on interest rate swaps designated as cash flow hedges (net of tax benefit of zero and zero, respectively) (1)	1	1	1	[1]	1	[1]
Settlement loss on pension plan (net of tax benefit of zero and zero, respectively) (2)	'	'	2	[2]	0	[2]
Amortization of unrecognized prior service credit and actuarial loss (net of tax benefit of zero, zero, zero and $1 million, respectively)	-1	0	-1	[3]	2	[3]
Net current period other comprehensive income, net of tax	'	'	0		3
End of period	($11)	($37)	($11)		($37)
[1]	Amount related to the reclassification of mark-to-market losses on cash flow hedging activities and was recorded in Interest expense on our unaudited consolidated statements of operations. Please read Note 4—Risk Management, Derivatives and Financial Instruments for further discussion.
[2]	Amount related to the settlement loss on the EEI pension plan and is included in the computation of total benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.
[3]	Amounts are associated with our defined benefit pension and other post-employment benefit plans and are included in the computation of net periodic benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Equity [Abstract]	'	'	'		'
Tax on actuarial loss due to pension plan remeasurement	'	'	$1		$0
Tax on reclassification of mark-to-market losses to earnings on interest rate swaps designated as cash flow hedges	0	0	0	[1]	0	[1]
Tax on pension plan settlement loss	0	0	0	[2]	0	[2]
Tax on amortization of unrecognized prior service credit and actuarial loss	'	'	$0	[3]	$1	[3]
[1]	Amount related to the reclassification of mark-to-market losses on cash flow hedging activities and was recorded in Interest expense on our unaudited consolidated statements of operations. Please read Note 4—Risk Management, Derivatives and Financial Instruments for further discussion.
[2]	Amount related to the settlement loss on the EEI pension plan and is included in the computation of total benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.
[3]	Amounts are associated with our defined benefit pension and other post-employment benefit plans and are included in the computation of net periodic benefit cost (gain). Please read Note 12—Pension and Other Post-Employment Benefits for further discussion.

Inventory_Details

Inventory (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Inventory Disclosure [Abstract]	'	'
Materials and supplies	$30	$33
Coal	37	43
Fuel oil	2	2
Total	$69	$78

Debt_Schedule_of_Longterm_Debt

Debt (Schedule of Long-term Debt Outstanding (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Debt Instrument [Line Items]	'		'
Total long-term debt, gross	$825		$825
Unamortized discount	-1		-1
Total Long-term Debt	824		824
Genco restricted payment interest coverage ratio minimum	1.75%	[1]	'
Genco additional indebtedness interest coverage ratio minimum	2.50%	[2]	'
Genco additional indebtedness debt-to-capital ratio maximum	60.00%	[2]	'
Debt Instrument, Covenant Compliance, Dividend Restrictions, Interest Coverage Ratio Determination Period	'1 year		'
Debt Instrument, Covenant Compliance, Dividend Restrictions, Projected Interest Coverage Ratio Determination Period	'2 years		'
Unsecured Debt | 7.95% Senior Notes Series F, due 2032	'		'
Debt Instrument [Line Items]	'		'
Face Amount	275		275
Debt Instrument, Interest Rate, Stated Percentage	7.95%		'
Unsecured Debt | 7.00% Senior Notes Series H, due 2018	'		'
Debt Instrument [Line Items]	'		'
Face Amount	300		300
Debt Instrument, Interest Rate, Stated Percentage	7.00%		'
Unsecured Debt | 6.30% Senior Notes Series I, due 2020	'		'
Debt Instrument [Line Items]	'		'
Face Amount	$250		$250
Debt Instrument, Interest Rate, Stated Percentage	6.30%		'
[1]	As of the date of a restricted payment, as defined, the minimum ratio must have been achieved for the most recently ended four fiscal quarters and projected by management to be achieved for each of the subsequent four six-month periods.
[2]	Ratios must be computed on a pro forma basis considering the additional indebtedness to be incurred and the related interest expense. Other borrowings from third-party external sources are included in the definition of indebtedness and are subject to these incurrence tests.

Related_Party_Transactions_Sch

Related Party Transactions (Schedule of Related Party Transactions) (Details) (USD $)

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Feb. 26, 2014

Feb. 26, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

In Millions, unless otherwise specified

Power Supply Agreements

Power Supply Agreements

Power Supply Agreements

Power Supply Agreements

Other affiliates

Other affiliates

Other affiliates

Other affiliates

Services Agreement

Services Agreement

Services Agreement

Services Agreement

Collateral Agreement with IPM

Collateral Agreement with IPM

Collateral Agreement with IPM

EEI Power Supply Agreement

EEI Power Supply Agreement

EEI Power Supply Agreement

EEI Power Supply Agreement

Accounts Receivable, Affiliates

Accounts Receivable, Affiliates

Accounts Receivable, Affiliates

Accounts Receivable, Affiliates

Accounts Payable, Affiliates

Accounts Payable, Affiliates

Accounts Payable, Affiliates

Accounts Payable, Affiliates

Revenues

Revenues

Revenues

Revenues

Revenues

Revenues

Revenues

Revenues

Operating and Maintenance Expense

Operating and Maintenance Expense

Operating and Maintenance Expense

Operating and Maintenance Expense

Maximum

Cost of Sales

Cost of Sales

Cost of Sales

Cost of Sales

Power Supply Agreements

Power Supply Agreements

Other affiliates

Other affiliates

Power Supply Agreements

Power Supply Agreements

Other affiliates

Other affiliates

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Accounts receivable, affiliates

$51

$59

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$50

$58

$1

$1

'

'

'

'

Accounts payable, affiliates

6

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

6

0

Revenues

'

'

162

219

480

557

0

1

0

5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expenses

'

'

'

'

'

'

'

'

'

'

10

2

31

8

'

'

'

0

47

0

65

'

'

'

'

'

'

'

'

Collateral amount, if any

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

15

22.5

'

'

'

'

'

'

'

'

'

'

'

'

Collateral amount, additional demand

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$7.50

'

'

'

'

'

'

'

'

'

'

'

'

'

Pension_and_Other_PostEmployme2

Pension and Other Post-Employment Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits	'	'	'	'
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'	'
Service cost benefits earned during the period	$1	$1	$2	$3
Interest cost on projected benefit obligation	1	2	3	7
Expected return on plan assets	-1	-3	-3	-10
Amortization of:	'	'	'	'
Prior service credit	0	0	0	0
Actuarial loss	0	2	0	6
Net periodic benefit cost (gain)	1	2	2	6
Settlements	'	'	2	0
Total benefit cost (gain)	'	'	4	6
Other post-employment Benefits	'	'	'	'
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]	'	'	'	'
Service cost benefits earned during the period	1	0	1	1
Interest cost on projected benefit obligation	1	1	2	3
Expected return on plan assets	-1	-1	-3	-4
Amortization of:	'	'	'	'
Prior service credit	-1	-2	-3	-6
Actuarial loss	0	1	2	3
Net periodic benefit cost (gain)	0	-1	-1	-3
Settlements	'	'	0	0
Total benefit cost (gain)	'	'	-1	-3
Ameren Services Company	'	'	'	'
Amortization of:	'	'	'	'
Net periodic benefit cost (gain)	'	$1	'	$2