Ameren Illinois (AILIN) 10-K 3 Mar 14 2013 FY Annual report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Jan. 31, 2014	Jun. 28, 2013
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Trading Symbol	'AEE	'	'
Entity Registrant Name	'AMEREN CORP	'	'
Entity Central Index Key	'0001002910	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	242,634,671	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Public Float	'	'	$8,356,338,069
Entity Well-known Seasoned Issuer	'Yes	'	'
Union Electric Company	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Trading Symbol	'AEE	'	'
Entity Registrant Name	'UNION ELECTRIC CO	'	'
Entity Central Index Key	'0000100826	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Non-accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	102,123,834	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Well-known Seasoned Issuer	'No	'	'
Ameren Illinois Company	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Trading Symbol	'AEE	'	'
Entity Registrant Name	'Ameren Illinois Co	'	'
Entity Central Index Key	'0000018654	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Filer Category	'Non-accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	25,452,373	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Well-known Seasoned Issuer	'No	'	'

Consolidated_Statement_Of_Inco

Consolidated Statement Of Income (Loss) (USD $)	12 Months Ended
Share data in Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Operating Revenues:	'		'		'
Electric	$4,832,000,000		$4,857,000,000		$5,147,000,000
Gas	1,006,000,000		924,000,000		1,001,000,000
Total operating revenues	5,838,000,000		5,781,000,000		6,148,000,000
Operating Expenses:	'		'		'
Fuel	845,000,000		714,000,000		866,000,000
Purchased power	502,000,000		780,000,000		952,000,000
Gas purchased for resale	526,000,000		472,000,000		570,000,000
Other operations and maintenance	1,617,000,000		1,511,000,000		1,562,000,000
Loss from regulatory disallowance	'		'		89,000,000
Impairment and other charges	'		'		'
Depreciation and amortization	706,000,000		673,000,000		643,000,000
Taxes other than income taxes	458,000,000		443,000,000		433,000,000
Total operating expenses	4,654,000,000		4,593,000,000		5,115,000,000
Operating Income	1,184,000,000		1,188,000,000		1,033,000,000
Other Income and Expenses:	'		'		'
Miscellaneous income	69,000,000	[1]	70,000,000	[1]	68,000,000	[1]
Miscellaneous expense	26,000,000	[1]	37,000,000	[1]	23,000,000	[1]
Total other income (expense)	43,000,000		33,000,000		45,000,000
Interest charges	398,000,000		392,000,000		387,000,000
Income Before Income Taxes	829,000,000		829,000,000		691,000,000
Income taxes	311,000,000	[1]	307,000,000	[1]	254,000,000	[1]
Income from Continuing Operations	518,000,000		522,000,000		437,000,000
Income (Loss) from Discontinued Operations, Net of Tax (Note 16)	-223,000,000		-1,496,000,000		89,000,000
Net Income (Loss)	295,000,000		-974,000,000		526,000,000
Less: Net Income (Loss) Attributable to Noncontrolling Interests:	'		'		'
Continuing Operations	6,000,000		6,000,000		6,000,000
Discontinued Operations	'		-6,000,000		1,000,000
Net Income (Loss):	'		'		'
Net income attributable to Ameren Corporation - continuing operations	512,000,000		516,000,000		431,000,000
Discontinued Operations	-223,000,000		-1,490,000,000		88,000,000
Net income (loss) attributable to Ameren Corporation	289,000,000		-974,000,000		519,000,000
Pension and other postretirement activity, net of income taxes (benefit)	30,000,000		-8,000,000		-19,000,000
Comprehensive Income (Loss)	300,000,000		-932,000,000		486,000,000
Earnings (Loss) per Common Share – Basic:	'		'		'
Continuing Operations - Basic	$2.11		$2.13		$1.79
Discontinued Operations - Basic	($0.92)		($6.14)		$0.36
Earnings (Loss) per Common Share – Basic	$1.19		($4.01)		$2.15
Earnings (Loss) per Common Share – Diluted:	'		'		'
Continuing Operations - Diluted	$2.10		$2.13		$1.79
Discontinued Operations - Diluted	($0.92)		($6.14)		$0.36
Earnings (Loss) per Common Share – Diluted	$1.18		($4.01)		$2.15
Dividends per Common Share	$1.60		$1.60		$1.55
Average Common Shares Outstanding - Basic	242.6		242.6		241.5
Average Common Shares Outstanding - Diluted	244.5		243		242.1
Union Electric Company	'		'		'
Operating Revenues:	'		'		'
Electric	3,379,000,000		3,132,000,000		3,222,000,000
Gas	161,000,000		139,000,000		156,000,000
Other	1,000,000		1,000,000		5,000,000
Total operating revenues	3,541,000,000		3,272,000,000		3,383,000,000
Operating Expenses:	'		'		'
Fuel	845,000,000		714,000,000		866,000,000
Purchased power	127,000,000		78,000,000		104,000,000
Gas purchased for resale	78,000,000		64,000,000		77,000,000
Other operations and maintenance	915,000,000		827,000,000		934,000,000
Loss from regulatory disallowance	'		'		89,000,000
Depreciation and amortization	454,000,000		440,000,000		408,000,000
Taxes other than income taxes	319,000,000		304,000,000		296,000,000
Total operating expenses	2,738,000,000		2,427,000,000		2,774,000,000
Operating Income	803,000,000		845,000,000		609,000,000
Other Income and Expenses:	'		'		'
Miscellaneous income	58,000,000		63,000,000		61,000,000
Miscellaneous expense	11,000,000		14,000,000		10,000,000
Total other income (expense)	47,000,000		49,000,000		51,000,000
Interest charges	210,000,000		223,000,000		209,000,000
Income Before Income Taxes	640,000,000		671,000,000		451,000,000
Income taxes	242,000,000		252,000,000		161,000,000
Net Income (Loss)	398,000,000		419,000,000		290,000,000
Net Income (Loss):	'		'		'
Net income (loss) attributable to Ameren Corporation	398,000,000		419,000,000		290,000,000
Other Comprehensive Income	'		'		'
Comprehensive Income (Loss)	398,000,000		419,000,000		290,000,000
Preferred Stock Dividends	3,000,000		3,000,000		3,000,000
Net Income Available to Common Stockholder	395,000,000		416,000,000		287,000,000
Ameren Illinois Company	'		'		'
Operating Revenues:	'		'		'
Electric	1,461,000,000		1,739,000,000		1,940,000,000
Gas	847,000,000		786,000,000		846,000,000
Other	3,000,000		'		1,000,000
Total operating revenues	2,311,000,000		2,525,000,000		2,787,000,000
Operating Expenses:	'		'		'
Purchased power	380,000,000		705,000,000		853,000,000
Gas purchased for resale	448,000,000		408,000,000		492,000,000
Other operations and maintenance	693,000,000		684,000,000		640,000,000
Depreciation and amortization	243,000,000		221,000,000		215,000,000
Taxes other than income taxes	132,000,000		130,000,000		129,000,000
Total operating expenses	1,896,000,000		2,148,000,000		2,329,000,000
Operating Income	415,000,000		377,000,000		458,000,000
Other Income and Expenses:	'		'		'
Miscellaneous income	10,000,000		7,000,000		7,000,000
Miscellaneous expense	9,000,000		17,000,000		6,000,000
Total other income (expense)	1,000,000		-10,000,000		1,000,000
Interest charges	143,000,000		129,000,000		136,000,000
Income Before Income Taxes	273,000,000		238,000,000		323,000,000
Income taxes	110,000,000		94,000,000		127,000,000
Net Income (Loss)	163,000,000		144,000,000		196,000,000
Net Income (Loss):	'		'		'
Net income (loss) attributable to Ameren Corporation	163,000,000		144,000,000		196,000,000
Pension and other postretirement activity, net of income taxes (benefit)	-3,000,000		-3,000,000		-3,000,000
Comprehensive Income (Loss)	160,000,000		141,000,000		193,000,000
Preferred Stock Dividends	3,000,000		3,000,000		3,000,000
Net Income Available to Common Stockholder	$160,000,000		$141,000,000		$193,000,000
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

Consolidated_Statement_Of_Inco1

Consolidated Statement Of Income (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension and other postretirement activity, tax (benefit)	$16	($6)	($14)
Ameren Illinois Company	'	'	'
Pension and other postretirement activity, tax (benefit)	$2	$2	$2

Consolidated_Statement_Of_Comp

Consolidated Statement Of Comprehensive Income (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income from Continuing Operations	$518	$522	$437
Pension and other postretirement activity, net of income taxes (benefit)	30	-8	-19
Comprehensive Income (Loss) from Continuing Operations	548	514	418
Less: Comprehensive Income from Continuing Operations Attributable to Noncontrolling Interests	6	6	6
Comprehensive Income from Continuing Operations Attributable to Ameren Corporation	542	508	412
Income (Loss) from Discontinued Operations, Net of Tax (Note 16)	-223	-1,496	89
Comprehensive Income from Continuing Operations Attributable to Ameren Corporation	-18	58	-20
Comprehensive Income (Loss) from Discontinued Operations	-241	-1,438	69
Less: Comprehensive Income from Discontinuing Operations Attributable to Noncontrolling Interest	1	2	-5
Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Corporation	-242	-1,440	74
Comprehensive Income (Loss)	300	-932	486
Ameren Illinois Company	'	'	'
Pension and other postretirement activity, net of income taxes (benefit)	-3	-3	-3
Comprehensive Income (Loss)	$160	$141	$193

Consolidated_Statement_Of_Comp1

Consolidated Statement Of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension and other postretirement activity, tax (benefit)	$16	($6)	($14)
Other Comprehensive Income (Loss) from Discontinued Operations Tax (Benefit)	($10)	$40	($14)

Consolidated_Balance_Sheet

Consolidated Balance Sheet (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Current Assets:	'		'
Cash and cash equivalents	$30		$184
Accounts receivable - trade (less allowance for doubtful accounts)	404		354
Unbilled revenue	304		291
Miscellaneous accounts and notes receivable	196		71
Materials and supplies	526		570
Current regulatory assets	156		247
Current accumulated deferred income taxes, net	106		170
Other current assets	85		98
Assets of discontinued operations (Note 16)	165		1,611
Total current assets	1,972		3,596
Property, Plant and Equipment, Net	16,205	[1],[2]	15,348	[1],[2]
Investments and Other Assets:	'		'
Nuclear decommissioning trust fund	494		408
Goodwill	411		411
Intangible assets	22		14
Regulatory assets	1,240		1,786
Other assets	698		667
Total investments and other assets	2,865		3,286
TOTAL ASSETS	21,042		22,230
Current Liabilities:	'		'
Current maturities of long-term debt	534		355
Short-term debt	368		'
Accounts and wages payable	806		533
Taxes accrued	55		49
Interest accrued	86		89
Customer deposits	105		107
Mark-to-market derivative liabilities	52		92
Current regulatory liabilities	216		100
Other current liabilities	194		168
Liabilities of discontinued operations (Note 16)	45		1,193
Total current liabilities	2,461		2,686
Long-term Debt, Net	5,504		5,802
Deferred Credits and Other Liabilities:	'		'
Accumulated deferred income taxes, net	3,166		3,186
Accumulated deferred investment tax credits	63		70
Regulatory liabilities	1,705		1,589
Asset retirement obligations	369		349
Pension and other postretirement benefits	466		1,138
Other deferred credits and liabilities	622		643
Total deferred credits and other liabilities	6,391		6,975
Commitments and Contingencies (Notes 2, 10, 14 and 15)	'		'
Stockholders' Equity:	'		'
Common stock	2		2
Other paid-in capital, principally premium on common stock	5,632		5,616
Preferred stock not subject to mandatory redemption	142		142
Retained earnings	907		1,006
Accumulated other comprehensive income (loss)	3		-8
Total stockholders' equity	6,544		6,616
Noncontrolling Interests	142		151
Total equity	6,686		6,767
TOTAL LIABILITIES AND EQUITY	21,042		22,230
Union Electric Company	'		'
Current Assets:	'		'
Cash and cash equivalents	1		148
Advances to money pool	'		24
Accounts receivable - trade (less allowance for doubtful accounts)	191		161
Accounts receivable - affiliates	1		4
Unbilled revenue	168		145
Miscellaneous accounts and notes receivable	57		48
Materials and supplies	352		397
Current regulatory assets	118		163
Current accumulated deferred income taxes, net	20		26
Other current assets	71		69
Total current assets	959		1,159
Property, Plant and Equipment, Net	10,452	[1]	10,161	[1]
Investments and Other Assets:	'		'
Nuclear decommissioning trust fund	494		408
Intangible assets	22		14
Regulatory assets	534		852
Other assets	443		449
Total investments and other assets	1,493		1,723
TOTAL ASSETS	12,904		13,043
Current Liabilities:	'		'
Current maturities of long-term debt	109		205
Due to Related Parties, Current	105		'
Accounts and wages payable	387		345
Accounts payable - affiliates	30		66
Taxes accrued	220		28
Interest accrued	57		60
Current regulatory liabilities	57		18
Other current liabilities	82		77
Total current liabilities	1,047		799
Long-term Debt, Net	3,648		3,801
Deferred Credits and Other Liabilities:	'		'
Accumulated deferred income taxes, net	2,509		2,443
Accumulated deferred investment tax credits	59		64
Regulatory liabilities	1,041		917
Asset retirement obligations	366		346
Pension and other postretirement benefits	189		461
Other deferred credits and liabilities	52		158
Total deferred credits and other liabilities	4,216		4,389
Commitments and Contingencies (Notes 2, 10, 14 and 15)	'		'
Stockholders' Equity:	'		'
Common stock	511		511
Other paid-in capital, principally premium on common stock	1,560		1,556
Preferred stock not subject to mandatory redemption	80		80
Retained earnings	1,842		1,907
Total stockholders' equity	3,993		4,054
TOTAL LIABILITIES AND EQUITY	12,904		13,043
Ameren Illinois Company	'		'
Current Assets:	'		'
Cash and cash equivalents	1		'
Accounts receivable - trade (less allowance for doubtful accounts)	201		182
Accounts receivable - affiliates	'		10
Unbilled revenue	135		146
Miscellaneous accounts and notes receivable	13		22
Materials and supplies	174		173
Current regulatory assets	38		84
Current accumulated deferred income taxes, net	45		85
Other current assets	26		47
Total current assets	633		749
Property, Plant and Equipment, Net	5,589		5,052
Investments and Other Assets:	'		'
Intercompany tax receivable – Genco	'		39
Goodwill	411		411
Regulatory assets	701		934
Other assets	120		97
Total investments and other assets	1,232		1,481
TOTAL ASSETS	7,454		7,282
Current Liabilities:	'		'
Current maturities of long-term debt	'		150
Borrowings from money pool	56		24
Accounts and wages payable	243		146
Accounts payable - affiliates	18		86
Taxes accrued	23		18
Customer deposits	79		85
Mark-to-market derivative liabilities	36		77
Environmental remediation	43		37
Current regulatory liabilities	159		82
Other current liabilities	114		92
Total current liabilities	771		797
Long-term Debt, Net	1,856		1,577
Deferred Credits and Other Liabilities:	'		'
Accumulated deferred income taxes, net	1,116		1,025
Accumulated deferred investment tax credits	4		5
Regulatory liabilities	664		672
Pension and other postretirement benefits	197		406
Accrued Environmental Loss Contingencies, Noncurrent	232		216
Other deferred credits and liabilities	166		183
Total deferred credits and other liabilities	2,379		2,507
Commitments and Contingencies (Notes 2, 10, 14 and 15)	'		'
Stockholders' Equity:	'		'
Common stock	0		0
Other paid-in capital, principally premium on common stock	1,965		1,965
Preferred stock not subject to mandatory redemption	62		62
Retained earnings	410		360
Accumulated other comprehensive income (loss)	11		14
Total stockholders' equity	2,448		2,401
TOTAL LIABILITIES AND EQUITY	$7,454		$7,282
[1]	(a)Amounts in Ameren and Ameren Missouri include two electric generation CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $228 million at December 31, 2013, and $228 million at December 31, 2012. The total accumulated depreciation associated with the two CTs was $56 million and $52 million at December 31, 2013, and 2012, respectively. In addition, Ameren Missouri has investments in debt securities, which were classified as held-to-maturity, related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2013, and 2012, the carrying value of these debt securities was $299 million and $304 million, respectively.
[2]	(b)Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Consolidated_Balance_Sheet_Par

Consolidated Balance Sheet (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, except Share data, unless otherwise specified
Accounts receivable - trade, allowance for doubtful accounts	$18	$17
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares outstanding	242,600,000	242,600,000
Union Electric Company	'	'
Accounts receivable - trade, allowance for doubtful accounts	5	5
Common stock, par value	$5	$5
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares outstanding	102,100,000	102,100,000
Ameren Illinois Company	'	'
Accounts receivable - trade, allowance for doubtful accounts	$13	$12
Common Stock, No Par Value	'	'
Common stock, shares authorized	45,000,000	45,000,000
Common stock, shares outstanding	25,500,000	25,500,000

Consolidated_Statement_Of_Cash

Consolidated Statement Of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Cash Flows From Operating Activities:	'		'		'
Net income (loss)	$295		($974)		$526
(Income) Loss from discontinued operations, net of tax	223		1,496		-89
Adjustments to reconcile net income to net cash provided by operating activities:	'		'		'
Depreciation and amortization	666		633		602
Amortization of nuclear fuel	71		83		61
Amortization of debt issuance costs and premium/discounts	24		20		16
Deferred income taxes and investment tax credits, net	410		257		262
Allowance for equity funds used during construction	-37	[1]	-36	[1]	-34	[1]
Share-based Compensation	27		29		17
Loss from regulatory disallowance	'		'		89
Other	23		-7		1
Changes in assets and liabilities:	'		'		'
Receivables	-60		30		200
Materials and supplies	60		-28		-29
Accounts and wages payable	81		-34		-28
Taxes accrued	-195		-4		-5
Assets, other	2		-6		59
Liabilities, other	33		65		-85
Pension and other postretirement benefits	-28		-23		-100
Counterparty collateral, net	41		41		36
Premiums paid on long-term debt repurchases	'		138		'
Net cash provided by operating activities - continuing operations	1,636		1,404		1,499
Net cash provided by operating activities - discontinued operations	57		286		379
Net cash provided by operating activities	1,693		1,690		1,878
Cash Flows From Investing Activities:	'		'		'
Capital expenditures	-1,379		-1,063		-881
Nuclear fuel expenditures	-45		-91		-62
Purchases of securities - nuclear decommissioning trust fund	-214		-403		-220
Sales and maturities of securities - nuclear decommissioning trust fund	196		384		199
Tax grants received related to renewable energy properties	'		18		'
Other	2		2		15
Net cash used in investing activities - continuing operations	-1,440		-1,153		-949
Net cash used in investing activities - discontinued operations	-283		-157		-99
Net cash used in investing activities	-1,723		-1,310		-1,048
Cash Flows From Financing Activities:	'		'		'
Dividends on common stock	-388		-382		-375
Dividends paid to noncontrolling interest holders	-6		-6		-6
Short-term debt and credit facility repayments, net	368		-148		-481
Redemptions, repurchases, and maturities:	'		'		'
Long-term debt	-399		-760		-155
Issuances:	'		'		'
Long-term debt	278		882		'
Common stock	'		'		65
Capital issuance costs	-2		-16		0
Advances received for construction	1		4		5
Repayments of advances received for construction	-1		'		-73
Net cash provided by (used in) financing activities - continuing operations	-149		-426		-1,020
Net cash provided by (used in) financing activities - discontinued operations	'		'		-100
Net cash provided by (used in) financing activities	-149		-426		-1,120
Net change in cash and cash equivalents	-179		-46		-290
Cash and cash equivalents at beginning of year	209		255		545
Cash and cash equivalents at end of year	30		209		255
Less: Cash and cash equivalents of discontinued operations at end of year	'		25		7
Cash and cash equivalents at beginning of year	184		248		'
Cash and cash equivalents at end of year	30		184		248
Noncash financing activity – dividends on common stock	'		7		'
Cash Paid (Refunded) During the Year:	'		'		'
Interest net of capitalized	393		433		453
Income taxes, net	8		1		-61
Union Electric Company	'		'		'
Cash Flows From Operating Activities:	'		'		'
Net income (loss)	398		419		290
Adjustments to reconcile net income to net cash provided by operating activities:	'		'		'
Depreciation and amortization	419		407		377
Amortization of nuclear fuel	71		83		61
FAC prudence review charge	26		'		18
Amortization of debt issuance costs and premium/discounts	7		6		6
Deferred income taxes and investment tax credits, net	65		287		155
Allowance for equity funds used during construction	-31		-31		-30
Loss from regulatory disallowance	'		'		89
Other	1		8		-8
Changes in assets and liabilities:	'		'		'
Receivables	-59		27		66
Materials and supplies	45		-48		-7
Accounts and wages payable	42		-27		12
Taxes accrued	100		-46		-6
Assets, other	47		-35		79
Liabilities, other	10		14		-48
Pension and other postretirement benefits	2		2		2
Premiums paid on long-term debt repurchases	'		62		'
Net cash provided by operating activities	1,143		1,004		1,056
Cash Flows From Investing Activities:	'		'		'
Capital expenditures	-648		-595		-550
Nuclear fuel expenditures	-45		-91		-62
Purchases of securities - nuclear decommissioning trust fund	-214		-403		-220
Sales and maturities of securities - nuclear decommissioning trust fund	196		384		199
Money pool advances, net	24		-24		'
Tax grants received related to renewable energy properties	'		18		'
Other	'		8		6
Net cash used in investing activities	-687		-703		-627
Cash Flows From Financing Activities:	'		'		'
Dividends on common stock	-460		-400		-403
Dividends on preferred stock	-3		-3		-3
Money pool borrowings, net	105		'		'
Redemptions, repurchases, and maturities:	'		'		'
Long-term debt	-249		-427		-5
Issuances:	'		'		'
Long-term debt	'		482		'
Capital issuance costs	'		-7		'
Capital contribution from parent	4		1		'
Repayments of advances received for construction	'		'		-19
Net cash provided by (used in) financing activities	-603		-354		-430
Net change in cash and cash equivalents	-147		-53		-1
Cash and cash equivalents at beginning of year	148		201		202
Cash and cash equivalents at end of year	1		148		201
Cash Paid (Refunded) During the Year:	'		'		'
Interest net of capitalized	212		220		210
Income taxes, net	86		-3		9
Ameren Illinois Company	'		'		'
Cash Flows From Operating Activities:	'		'		'
Net income (loss)	163		144		196
Adjustments to reconcile net income to net cash provided by operating activities:	'		'		'
Depreciation and amortization	238		214		206
Amortization of debt issuance costs and premium/discounts	15		11		8
Deferred income taxes and investment tax credits, net	104		104		155
Allowance for equity funds used during construction	-6		-5		-4
Other	4		-11		-14
Changes in assets and liabilities:	'		'		'
Receivables	50		23		146
Materials and supplies	15		20		-21
Accounts and wages payable	19		-21		-46
Taxes accrued	28		3		-12
Assets, other	-53		22		-3
Liabilities, other	33		72		-30
Pension and other postretirement benefits	-8		-26		-101
Counterparty collateral, net	43		40		20
Premiums paid on long-term debt repurchases	'		76		'
Net cash provided by operating activities	651		519		504
Cash Flows From Investing Activities:	'		'		'
Capital expenditures	-701		-442		-351
Returns from (advances to) ATXI for construction	'		'		49
Other	6		5		6
Net cash used in investing activities	-695		-437		-296
Cash Flows From Financing Activities:	'		'		'
Dividends on common stock	-110		-189		-327
Dividends on preferred stock	-3		-3		-3
Money pool borrowings, net	32		24		'
Redemptions, repurchases, and maturities:	'		'		'
Long-term debt	-150		-333		-150
Issuances:	'		'		'
Long-term debt	278		400		'
Capital issuance costs	-2		-6		'
Capital contribution from parent	'		'		19
Advances received for construction	1		4		5
Repayments of advances received for construction	-1		'		-53
Net cash provided by (used in) financing activities	45		-103		-509
Net change in cash and cash equivalents	1		-21		-301
Cash and cash equivalents at beginning of year	'		21		322
Cash and cash equivalents at end of year	1		'		21
Cash Paid (Refunded) During the Year:	'		'		'
Interest net of capitalized	112		125		137
Income taxes, net	($23)		($22)		($14)
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

Consolidated_Statement_Of_Cash1

Consolidated Statement Of Cash Flows (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Union Electric Company	'	'	'
Capitalized interest	$16	$15	$25
Ameren Illinois Company	'	'	'
Capitalized interest	$4	$2	$2

Consolidated_Statement_Of_Stoc

Consolidated Statement Of Stockholders' Equity (USD $)

Total

Common Stock

Other Paid-In Capital

Retained Earnings

Derivative Financial Instruments

Deferred Retirement Benefit Costs

Accumulated Other Comprehensive Income (Loss)

Noncontrolling Interest

Total Ameren Corporation Stockholders' Equity

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

In Millions, unless otherwise specified

Common Stock

Other Paid-In Capital

Preferred Stock Not Subject To Mandatory Redemption

Retained Earnings

Common Stock

Other Paid-In Capital

Preferred Stock Not Subject To Mandatory Redemption

Retained Earnings

Deferred Retirement Benefit Costs

Accumulated Other Comprehensive Income (Loss)

Beginning of year at Dec. 31, 2010

'

$2

$5,520

$2,225

$0

($17)

'

$154

'

'

'

$1,555

'

$2,007

'

'

$1,952

$62

$542

$20

'

Beginning of year (shares) at Dec. 31, 2010

240.4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

526

'

'

'

'

'

'

'

'

290

'

'

'

290

196

'

'

'

196

'

'

Net income (loss) attributable to Ameren Corporation

519

'

'

519

'

'

'

'

'

290

'

'

'

'

196

'

'

'

'

'

'

Shares issued (value)

'

'

65

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares issued (number of shares)

2.2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock-based compensation activity

'

'

13

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capital contribution from parent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

19

'

13

'

'

'

'

Common stock dividends

'

'

'

-375

'

'

'

'

'

'

'

'

'

-403

'

'

'

'

-327

'

'

Preferred stock dividends

'

'

'

'

'

'

'

'

'

'

'

'

'

-3

'

'

'

'

-3

'

'

Change in derivative financial instruments

'

'

'

'

7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Divestiture of derivative financial instruments

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Change in deferred retirement benefit costs

19

'

'

'

'

-40

'

'

'

'

'

'

'

'

3

'

'

'

'

'

-3

Divestiture of deferred retirement benefit costs

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to noncontrolling interest holder

'

'

'

'

'

'

'

7

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends paid to noncontrolling interest holders

'

'

'

'

'

'

'

-6

'

'

'

'

'

'

'

'

'

'

'

'

'

Divestiture of noncontrolling interest

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Other

'

'

'

'

'

'

'

-6

'

'

'

'

'

'

'

'

'

'

'

'

'

Total stockholders' equity

'

'

'

'

'

'

'

'

7,919

4,037

'

'

'

'

2,452

'

'

'

'

'

'

Stockholders' equity, end of year at Dec. 31, 2011

'

'

'

'

'

'

'

'

7,919

4,037

'

'

'

'

2,452

'

'

'

'

'

'

End of year at Dec. 31, 2011

8,068

2

5,598

2,369

7

-57

-50

149

'

'

511

1,555

80

1,891

'

'

1,965

62

408

17

17

End of year (shares) at Dec. 31, 2011

242.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

-403

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Ameren Corporation

-403

'

'

'

'

'

'

'

'

22

'

'

'

'

28

'

'

'

'

'

'

Stockholders' equity, end of year at Mar. 31, 2012

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Beginning of year at Dec. 31, 2011

8,068

2

5,598

2,369

7

-57

-50

149

'

'

511

1,555

80

1,891

'

'

1,965

62

408

17

17

Beginning of year (shares) at Dec. 31, 2011

242.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

-974

'

'

'

'

'

'

'

'

419

'

'

'

419

144

'

'

'

144

'

'

Net income (loss) attributable to Ameren Corporation

-974

'

'

-974

'

'

'

'

'

419

'

'

'

'

144

'

'

'

'

'

'

Shares issued (value)

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares issued (number of shares)

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock-based compensation activity

'

'

18

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capital contribution from parent

'

'

'

'

'

'

'

'

'

1

'

1

'

'

'

'

0

'

'

'

'

Common stock dividends

'

'

'

-389

'

'

'

'

'

'

'

'

'

-400

'

'

'

'

-189

'

'

Preferred stock dividends

'

'

'

'

'

'

'

'

'

'

'

'

'

-3

'

'

'

'

-3

'

'

Change in derivative financial instruments

'

'

'

'

18

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Divestiture of derivative financial instruments

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Change in deferred retirement benefit costs

8

'

'

'

'

24

'

'

'

'

'

'

'

'

3

'

'

'

'

'

-3

Divestiture of deferred retirement benefit costs

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to noncontrolling interest holder

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends paid to noncontrolling interest holders

'

'

'

'

'

'

'

-6

'

'

'

'

'

'

'

'

'

'

'

'

'

Divestiture of noncontrolling interest

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Other

'

'

'

'

'

'

'

8

'

'

'

'

'

'

'

'

'

'

'

'

'

Total stockholders' equity

6,616

'

'

'

'

'

'

'

6,616

4,054

'

'

'

'

2,401

'

'

'

'

'

'

Stockholders' equity, end of year at Dec. 31, 2012

6,616

'

'

'

'

'

'

'

6,616

4,054

'

'

'

'

2,401

'

'

'

'

'

'

End of year at Dec. 31, 2012

6,767

2

5,616

1,006

25

-33

-8

151

'

'

511

1,556

80

1,907

'

'

1,965

62

360

14

14

End of year (shares) at Dec. 31, 2012

242.6

'

'

'

'

'

'

'

'

102.1

'

'

'

'

25.5

'

'

'

'

'

'

Beginning of year at Sep. 30, 2012

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

-1,155

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Ameren Corporation

-1,156

'

'

'

'

'

'

'

'

16

'

'

'

'

12

'

'

'

'

'

'

Total stockholders' equity

6,616

'

'

'

'

'

'

'

6,616

4,054

'

'

'

'

2,401

'

'

'

'

'

'

Stockholders' equity, end of year at Dec. 31, 2012

6,616

'

'

'

'

'

'

'

6,616

4,054

'

'

'

'

2,401

'

'

'

'

'

'

End of year at Dec. 31, 2012

6,767

2

'

'

'

'

-8

'

'

'

511

'

80

'

'

'

'

62

'

14

'

End of year (shares) at Dec. 31, 2012

242.6

'

'

'

'

'

'

'

'

102.1

'

'

'

'

25.5

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

-143

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Ameren Corporation

-145

'

'

'

'

'

'

'

'

41

'

'

'

'

32

'

'

'

'

'

'

Stockholders' equity, end of year at Mar. 31, 2013

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Beginning of year at Dec. 31, 2012

6,767

2

5,616

1,006

25

-33

-8

151

'

'

511

1,556

80

1,907

'

'

1,965

62

360

14

14

Beginning of year (shares) at Dec. 31, 2012

242.6

'

'

'

'

'

'

'

'

102.1

'

'

'

'

25.5

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

295

'

'

'

'

'

'

'

'

398

'

'

'

398

163

'

'

'

163

'

'

Net income (loss) attributable to Ameren Corporation

289

'

'

289

'

'

'

'

'

398

'

'

'

'

163

'

'

'

'

'

'

Shares issued (value)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares issued (number of shares)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock-based compensation activity

'

'

16

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capital contribution from parent

'

'

'

'

'

'

'

'

'

4

'

4

'

'

'

'

'

'

'

'

'

Common stock dividends

'

'

'

-388

'

'

'

'

'

'

'

'

'

-460

'

'

'

'

-110

'

'

Preferred stock dividends

'

'

'

'

'

'

'

'

'

'

'

'

'

-3

'

'

'

'

-3

'

'

Change in derivative financial instruments

'

'

'

'

-21

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Divestiture of derivative financial instruments

'

'

'

'

-4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Change in deferred retirement benefit costs

-30

'

'

'

'

29

'

'

'

'

'

'

'

'

3

'

'

'

'

'

-3

Divestiture of deferred retirement benefit costs

'

'

'

'

'

7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to noncontrolling interest holder

'

'

'

'

'

'

'

6

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends paid to noncontrolling interest holders

'

'

'

'

'

'

'

-6

'

'

'

'

'

'

'

'

'

'

'

'

'

Divestiture of noncontrolling interest

'

'

'

'

'

'

'

9

'

'

'

'

'

'

'

'

'

'

'

'

'

Other

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Total stockholders' equity

6,544

'

'

'

'

'

'

'

6,544

3,993

'

'

'

'

2,448

'

'

'

'

'

'

Stockholders' equity, end of year at Dec. 31, 2013

6,544

'

'

'

'

'

'

'

6,544

3,993

'

'

'

'

2,448

'

'

'

'

'

'

End of year at Dec. 31, 2013

6,686

2

5,632

907

0

3

3

142

'

'

511

1,560

80

1,842

'

'

1,965

'

410

11

11

End of year (shares) at Dec. 31, 2013

242.6

'

'

'

'

'

'

'

'

102.1

'

'

'

'

25.5

'

'

'

'

'

'

Beginning of year at Sep. 30, 2013

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Increase (Decrease) in Stockholders' Equity [Roll Forward]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss)

38

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) attributable to Ameren Corporation

37

'

'

'

'

'

'

'

'

33

'

'

'

'

22

'

'

'

'

'

'

Total stockholders' equity

6,544

'

'

'

'

'

'

'

6,544

3,993

'

'

'

'

2,448

'

'

'

'

'

'

Stockholders' equity, end of year at Dec. 31, 2013

6,544

'

'

'

'

'

'

'

6,544

3,993

'

'

'

'

2,448

'

'

'

'

'

'

End of year at Dec. 31, 2013

$6,686

$2

'

'

'

'

$3

'

'

'

$511

'

$80

'

'

'

'

'

'

$11

'

End of year (shares) at Dec. 31, 2013

242.6

'

'

'

'

'

'

'

'

102.1

'

'

'

'

25.5

'

'

'

'

'

'

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	'
	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
	General
	Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005, administered by FERC. Ameren’s primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of other expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below.
	•	Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri. This area has an estimated population of 2.8 million and includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 127,000 customers.
	•	Ameren Illinois Company, doing business as Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business in Illinois. Ameren Illinois was created by the merger of CILCO and IP with and into CIPS in 2010. CIPS was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to portions of central and southern Illinois having an estimated population of 3.1 million in an area of 40,000 square miles. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 767,000 customers.
	Ameren has various other subsidiaries responsible for activities such as the provision of shared services. Ameren also has a subsidiary, ATXI, that operates a FERC rate-regulated electric transmission business and is developing the Illinois Rivers project.
	On March 14, 2013, Ameren entered into a transaction agreement to divest New AER to IPH. On December 2, 2013, Ameren completed the divestiture of New AER to IPH. On January 31, 2014, Medina Valley completed its sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers to Rockland Capital. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information.
	As a result of the transaction agreement with IPH and Ameren’s plan to sell its Elgin, Gibson City, and Grand Tower gas-fired energy centers, Ameren determined that New AER and the gas-fired energy centers qualified for discontinued operations presentation beginning March 14, 2013. In addition, as of December 2, 2013, Ameren abandoned the Meredosia and Hutsonville energy centers upon the completion of the divestiture of New AER to IPH. Ameren is prohibited from operating these energy centers through December 31, 2020, as a provision of the Illinois Pollution Control Board's November 2013 order granting IPH a variance of the MPS. As a result, Ameren determined that the Meredosia and Hutsonville energy centers qualified for discontinued operations presentation as of December 2, 2013. The Meredosia and Hutsonville energy centers ceased operations at December 31, 2011, and therefore 2011 was the last year those energy centers had a material effect on Ameren's consolidated financial statements. As a result of these events, Ameren has segregated New AER’s and the Elgin, Gibson City, Grand Tower, Meredosia, and Hutsonville energy centers’ operating results, assets, and liabilities and presented them separately as discontinued operations for all periods presented in this report. Unless otherwise stated, these notes to the financial statements exclude discontinued operations for all periods presented. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information regarding that presentation.
	The financial statements of Ameren are prepared on a consolidated basis, and therefore include the accounts of its majority-owned subsidiaries. Ameren Missouri and Ameren Illinois have no subsidiaries and therefore their financial statements are not prepared on a consolidated basis. All significant intercompany transactions have been eliminated. All tabular dollar amounts are in millions, unless otherwise indicated.
	Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.
	Regulation
	Certain Ameren subsidiaries are regulated by the MoPSC, the ICC, and FERC. In accordance with authoritative accounting guidance regarding accounting for the effects of certain types of regulation, Ameren Missouri and Ameren Illinois defer certain costs as assets pursuant to actions of rate regulators or because of expectations that the companies will be able to recover such costs in rates charged to customers. Ameren Missouri and Ameren Illinois also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be returned to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. In addition to the cost recovery mechanisms discussed in the Purchased Gas, Power and Fuel Rate-adjustment Mechanisms section below, Ameren Missouri and Ameren Illinois have approvals from regulators to use other cost recovery mechanisms. Ameren Missouri has a vegetation management and infrastructure inspection cost tracker, a pension and postretirement benefit cost tracker, an uncertain tax positions tracker, a renewable energy standards cost tracker, a storm restoration cost tracker, and the MEEIA energy efficiency rider. In addition to participating in the IEIMA's formula rate regulatory framework, Ameren Illinois has an environmental cost rider, an asbestos-related litigation rider, an energy efficiency rider, and a bad debt rider. See Note 2 – Rate and Regulatory Matters for additional information on regulatory assets and liabilities. In addition, other costs that Ameren Missouri and Ameren Illinois expect to recover from customers are recorded as construction work in progress and property and plant, net. See Note 3 – Property and Plant, Net.
	Cash and Cash Equivalents
	Cash and cash equivalents include cash on hand and temporary investments purchased with an original maturity of three months or less.
	Allowance for Doubtful Accounts Receivable
	The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has a rate mechanism that adjusts rates for net write-offs of customer accounts receivable above or below those being collected in rates.
	Materials and Supplies
	Materials and supplies are recorded at the lower of cost or market. Cost is determined using the average-cost method. Materials and supplies are capitalized as inventory when purchased and then expensed or capitalized as plant assets when installed, as appropriate. The following table presents a breakdown of materials and supplies for each of the Ameren Companies at December 31, 2013, and 2012:
			Ameren Missouri				Ameren Illinois				Ameren
	2013
	Fuel(a)		$	144			$	—			$	144
	Gas stored underground		17				110				127
	Other materials and supplies		191				64				255
			$	352			$	174			$	526
	2012
	Fuel(a)		$	198			$	—			$	198
	Gas stored underground		18				113				131
	Other materials and supplies		181				60				241
			$	397			$	173			$	570
	(a)	Consists of coal, oil, and propane.
	Property and Plant
	We capitalize the cost of additions to and betterments of units of property and plant. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures, including nuclear refueling and maintenance outages, are expensed as incurred. When units of depreciable property are retired, the original costs, less salvage values, are charged to accumulated depreciation. Asset removal costs accrued by our rate-regulated operations that do not constitute legal obligations are classified as a regulatory liability. See Asset Retirement Obligations below and Note 3 – Property and Plant, Net, for additional information.
	Depreciation
	Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The provision for depreciation for the Ameren Companies in 2013, 2012 and 2011 ranged from 3% to 4% of the average depreciable cost.
	Allowance for Funds Used During Construction
	We capitalize allowance for funds used during construction, or the cost of borrowed funds and the cost of equity funds (preferred and common stockholders’ equity) applicable to rate-regulated construction expenditures, in accordance with the utility industry's accounting practice. Allowance for funds used during construction does not represent a current source of cash funds. This accounting practice offsets the effect on earnings of the cost of financing during construction, and it treats such financing costs in the same manner as construction charges for labor and materials.
	Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates. The following table presents the annual allowance for funds used during construction rates that were utilized during 2013, 2012 and 2011:
		2013			2012			2011
	Ameren Missouri	8	%		8	%		8	%
	Ameren Illinois	8	%		9	%		9	%
	Goodwill and Intangible Assets
	Goodwill. Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had recorded goodwill of $411 million at December 31, 2013, and 2012.
	Ameren has two reporting units, which also represent Ameren’s reportable segments. Ameren's reporting units are Ameren Missouri and Ameren Illinois. Ameren Illinois has one reporting unit, Ameren Illinois. Ameren’s and Ameren Illinois' reporting units have been defined and goodwill has been evaluated at the operating segment level in accordance with authoritative accounting guidance. Our reporting units represent businesses for which discrete financial information is available and reviewed regularly by management. All of Ameren's and Ameren Illinois' goodwill at December 31, 2013, and 2012, has been assigned to the Ameren Illinois reporting unit.
	We evaluate goodwill for impairment as of October 31 of each year, or more frequently if events and circumstances indicate that the asset might be impaired. Ameren and Ameren Illinois applied a qualitative goodwill evaluation model for their annual goodwill impairment test conducted as of October 31, 2013. Based on the results of Ameren’s and Ameren Illinois’ qualitative assessment, Ameren and Ameren Illinois believe it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value as of October 31, 2013, indicating no impairment of Ameren’s or Ameren Illinois’ goodwill. The following factors, among others, were considered by Ameren and Ameren Illinois when assessing whether it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value for the October 31, 2013, test:
	•	macroeconomic conditions, including those conditions within Ameren Illinois’ service territory;
	•	pending rate case outcomes and projections of future rate case outcomes;
	•	changes in laws and potential law changes;
	•	observable industry market multiples;
	•	achievement of IEIMA performance metrics and the yield of the 30-year United States treasury bonds; and
	•	actual and forecasted financial performance.
	The goodwill assigned to the Ameren Illinois reporting unit on the December 31, 2013, balance sheets of Ameren and Ameren Illinois had no accumulated goodwill impairment losses. Ameren and Ameren Illinois will continue to monitor the actual and forecasted operating results, cash flows, market capitalization, and observable industry market multiples of the Ameren Illinois reporting unit for signs of possible declines in estimated fair value and potential goodwill impairment.
	Intangible Assets. Ameren and Ameren Missouri classify emission allowances and renewable energy credits as intangible assets. Ameren Illinois consumes renewable energy credits as they are purchased through the IPA procurement process and expenses them immediately. We evaluate intangible assets for impairment if events or changes in circumstances indicate that their carrying amount might be impaired.
	At December 31, 2013, Ameren’s and Ameren Missouri’s intangible assets consisted of renewable energy credits obtained through wind and solar power purchase agreements. The book value of Ameren’s and Ameren Missouri’s renewable energy credits was $22 million and $22 million at December 31, 2013, respectively. The book value of Ameren's and Ameren Missouri's renewable energy credits was $14 million and $14 million at December 31, 2012, respectively.
	Renewable energy credits and emission allowances are charged to purchased power expense and fuel expense, respectively, as they are used in operations. In accordance with the MoPSC's 2012 electric rate order, most of Ameren Missouri's amortization of intangible assets is deferred as a regulatory asset pending future recovery from customers through rates. The following table presents amortization expense based on usage of renewable energy credits and emission allowances, net of gains from sales, for Ameren, Ameren Missouri, and Ameren Illinois during the years ended December 31, 2013, 2012, and 2011.
			2013			2012			2011
	Ameren Missouri	$	(a)		$	(a)		$	(a)
	Ameren Illinois		13			4			3
	Ameren	$	13		$	4		$	3
	(a)	Less than $1 million.
	Impairment of Long-lived Assets
	We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets with the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount of the carrying value that exceeds the estimated fair value of the assets. In the period in which we determine an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its fair value less cost to sell.
	During 2011, the MoPSC issued an electric rate order that disallowed the recovery of all costs of enhancements, or costs that would have been incurred absent the breach, related to the rebuilding of the Taum Sauk energy center in excess of the amount recovered from property insurance. Consequently, Ameren and Ameren Missouri each recorded a pretax charge to earnings of $89 million, which is reflected as "Taum Sauk regulatory disallowance" on each company's statement of income.
	Investments
Ameren and Ameren Missouri evaluate for impairment the investments held in Ameren Missouri’s nuclear decommissioning trust fund. Losses on assets in the trust fund could result in higher funding requirements for decommissioning costs, which Ameren Missouri believes would be recovered in electric rates paid by its customers. Accordingly, Ameren and Ameren Missouri recognize a regulatory asset on their balance sheets for losses on investments held in the nuclear decommissioning trust fund. See Note 9 – Nuclear Decommissioning Trust Fund Investments for additional information.
Environmental Costs
Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates. If environmental expenditures are related to facilities currently in use, such as pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset.
Unamortized Debt Discount, Premium, and Expense
Discount, premium, and expense associated with long-term debt are amortized over the lives of the related issues.
Revenue
Operating Revenues
The Ameren Companies record operating revenue for electric or natural gas service when it is delivered to customers. We accrue an estimate of electric and natural gas revenues for service rendered but unbilled at the end of each accounting period.
Beginning in 2012, Ameren Illinois elected to participate in the performance-based formula ratemaking framework pursuant to the IEIMA. The IEIMA provides for an annual reconciliation of Ameren Illinois' electric distribution revenue requirement. As of each balance sheet date, Ameren Illinois records its estimate of the electric distribution revenue impact resulting from the reconciliation of the revenue requirement necessary to reflect the actual costs incurred for that year with the revenue requirement that was in effect for billing purposes for that year. If the current year's revenue requirement is greater than the revenue requirement customer rates were based upon, an increase to electric operating revenues with an offset to a regulatory asset is recorded to reflect the expected recovery of those additional costs from customers within the next two years. If the current year's revenue requirement is less than the revenue requirement customer rates were based upon, a reduction to electric operating revenues with an offset to a regulatory liability is recorded to reflect the expected refund to customers within the next two years. See Note 2 – Rate and Regulatory Matters for information regarding Ameren Illinois' revenue requirement reconciliation pursuant to the IEIMA.
Similar to the IEIMA process described above, Ameren Illinois and ATXI record the impact of a revenue requirement reconciliation for each company's electric transmission jurisdiction, pursuant to FERC-approved rate treatment.
Nuclear Fuel
Ameren Missouri’s cost of nuclear fuel is capitalized and then amortized to fuel expense on a unit-of-production basis. Spent fuel disposal cost is based on net kilowatthours generated and sold. That cost is charged to "Operating Expenses – Fuel" in the statement of income.
Purchased Gas, Power and Fuel Rate-adjustment Mechanisms
Ameren Missouri and Ameren Illinois have various rate-adjustment mechanisms in place that provide for the recovery of purchased natural gas and electric fuel and purchased power costs. See Note 2 – Rate and Regulatory Matters for the regulatory assets and liabilities recorded at December 31, 2013, and 2012, related to the rate-adjustment mechanisms discussed below.
In Ameren Missouri’s and Ameren Illinois’ retail natural gas utility jurisdictions, changes in natural gas costs are reflected in billings to their natural gas utility customers through PGA clauses. The differences between actual natural gas costs and costs billed to customers in a given period are deferred as regulatory assets or liabilities. The deferred amounts are either billed or refunded to natural gas utility customers in a subsequent period.
In Ameren Illinois’ retail electric utility jurisdictions, changes in purchased power and transmission service costs are reflected in billings to their electric utility customers through pass-through rate-adjustment clauses. The differences between actual purchased power and transmission service costs and costs billed to customers in a given period are deferred as regulatory assets or liabilities. The deferred amounts are either billed or refunded to electric utility customers in a subsequent period.
Ameren Missouri has a FAC that allows an adjustment of electric rates three times per year for a pass-through to customers of 95% of changes in fuel, certain fuel additives, emission allowances, purchased power costs, transmission costs and revenues, and MISO costs and revenues, net of off-system sales revenues, greater or less than the amount set in base rates without a traditional rate proceeding, subject to MoPSC prudency review. The differences between the cost of fuel incurred and the cost of fuel recovered from Ameren Missouri customers' base rates are deferred as regulatory assets or liabilities. The deferred amounts are either billed or refunded to Ameren Missouri’s electric utility customers in a subsequent period.
Accounting for MISO Transactions
MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri and Ameren Illinois using settlement information provided by MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses - Purchased power” and net sales in a single hour in “Operating Revenues - Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses - Purchased Power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri and Ameren Illinois prior-period transactions will be resettled outside the routine settlement process because of a change in MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated, and the Ameren Companies recognize revenues once the resettlement amount is received.
Stock-based Compensation
Stock-based compensation cost is measured at the grant date based on the fair value of the award. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite service period. See Note 12 – Stock-based Compensation for additional information.
Excise Taxes
Excise taxes levied on us are reflected on Ameren Missouri electric customer bills and on Ameren Missouri and Ameren Illinois natural gas customer bills. They are recorded gross in “Operating Revenues – Electric,” “Operating Revenues – Gas” and “Operating Expenses – Taxes other than income taxes” on the statement of income (loss). Excise taxes reflected on Ameren Illinois electric customer bills are imposed on the customer and are therefore not included in revenues and expenses. They are included in “Taxes accrued” on the balance sheet. The following table presents excise taxes recorded in “Operating Revenues – Electric,” “Operating Revenues – Gas,” and “Operating Expenses – Taxes other than income taxes” for the years ended 2013, 2012 and 2011:
	2013				2012				2011
Ameren Missouri	$	152			$	139			$	137
Ameren Illinois	61				54				57
Ameren	$	213			$	193			$	194
Income Taxes
Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes, in accordance with authoritative accounting guidance. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates.
We recognize that regulators will probably reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in the deferred tax liability, which were recorded because of decreases in the statutory rate, have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery in rates of future income taxes, resulting from the reversal of the equity portion of the allowance for funds used during construction that was an unrecognized temporary difference prior to the adoption of the authoritative accounting guidance for income taxes.
Investment tax credits used on tax returns for prior years have been deferred in accordance with GAAP. The credits are being amortized over the useful lives of the related investment. Deferred income taxes were recorded on the temporary difference represented by the deferred investment tax credits and a corresponding regulatory liability. This recognizes the expected reduction in rate revenue for future lower income taxes associated with the amortization of the investment tax credits. See Note 13 – Income Taxes.
For certain renewable energy construction projects placed in service, Ameren Missouri elected to seek federal tax grants in lieu of the investment tax credits for which the projects also qualified. These grants were accounted for using a grant recognition accounting model. Ameren Missouri elected to reduce the basis of property as grants were received, which will reduce the amount of depreciation expense recognized in future periods. In 2012, Ameren Missouri received $18 million in federal tax grants.
Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax similar to that which would be owed had the party been separately subject to tax. Any net benefit attributable to the parent is reallocated to other members. That allocation is treated as a contribution of capital to the party receiving the benefit.
Noncontrolling Interests
As of December 31, 2013, Ameren’s noncontrolling interests included the preferred stock not subject to mandatory redemption of Ameren Missouri and Ameren Illinois. As of December 31, 2012, Ameren's noncontrolling interests also included the 20% of EEI not owned by Ameren. All noncontrolling interests are classified as a component of equity separate from Ameren’s equity in its consolidated balance sheet.
Earnings per Share
Basic earnings per share is computed by dividing net income attributable to Ameren Corporation by the weighted-average number of common shares outstanding during the period. Diluted earnings per share is computed by dividing net income attributable to Ameren Corporation by the diluted weighted-average number of common shares outstanding during the period. Diluted earnings per share reflects the potential dilution that would occur if certain stock-based performance share units were settled.
The following table presents Ameren’s basic and diluted earnings per share calculations and reconciles the weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the years ended December 31, 2013, 2012 and 2011:
	2013				2012				2011
Net income (loss) attributable to Ameren Corporation:
Continuing operations	$	512			$	516			$	431
Discontinued operations	(223		)		(1,490		)		88
Net income (loss) attributable to Ameren Corporation	$	289			$	(974	)		$	519
Average common shares outstanding – basic	242.6				242.6				241.5
Assumed settlement of performance share units	1.9				0.4				0.6
Average common shares outstanding – diluted	244.5				243				242.1
Earnings (loss) per common share – basic:
Continuing operations	$	2.11			$	2.13			$	1.79
Discontinued operations	(0.92		)		(6.14		)		0.36
Earnings (loss) per common share – basic	$	1.19			$	(4.01	)		$	2.15
Earnings (loss) per common share – diluted:
Continuing operations	$	2.1			$	2.13			$	1.79
Discontinued operations	(0.92		)		(6.14		)		0.36
Earnings (loss) per common share – diluted	$	1.18			$	(4.01	)		$	2.15
Average performance share units excluded from calculation(a)	0.1				0.7				—
(a)	Weighted-average number of performance share units that were excluded from the “Assumed settlement of performance share units” provided above because the performance or market conditions related to the awards had not yet been met.
Supplemental Cash Flow Information
The following table presents additional information regarding Ameren's consolidated statement of cash flows for the years ended December 31, 2013, 2012 and 2011:
	2013				2012				2011
Cash paid (refunded) during the year:
Interest
Continuing operations(a)	$	362			$	384			$	393
Discontinued operations(b)	31				49				60
	$	393			$	433			$	453
Income taxes, net
Continuing Operations	$	116			$	10			$	(47	)
Discontinued Operations	(108		)		(9		)		(14		)
	$	8			$	1			$	(61	)
(a)	Net of $20 million, $17 million, and $27 million capitalized, respectively.
(b)	Net of $17 million, $13 million, and $3 million capitalized, respectively.
See Note 3 – Property and Plant, Net, for information on accrued capital expenditures.
Accounting Changes and Other Matters
The following is a summary of recently adopted authoritative accounting guidance, as well as guidance issued but not yet adopted, that could affect the Ameren Companies.
Presentation of Comprehensive Income
In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance changed the presentation of comprehensive income in the financial statements. It requires entities to report components of comprehensive income either in a continuous statement of comprehensive income or in two separate but consecutive statements. This guidance was effective for the Ameren Companies beginning in the first quarter of 2012 with retroactive application required. The implementation of the amended guidance did not affect the Ameren Companies’ results of operations, financial position, or liquidity.
In February 2013, FASB amended this guidance to require an entity to provide information about the amounts reclassified out of accumulated OCI by component. In addition, an entity is required to present significant amounts reclassified out of accumulated OCI by the respective line items of net income either on the face of the statement where net income is presented or in the footnotes. This guidance was effective for the Ameren Companies beginning in the first quarter of 2013. The implementation of this amended guidance did not affect the Ameren Companies’ results of operations, financial position, or liquidity. The amounts reclassified out of accumulated OCI for the Ameren Companies corresponding to continuing operations related to pension and other postretirement plan activity. These amounts were immaterial for the year ended December 31, 2013, and therefore no additional disclosures were required.
Disclosures about Offsetting Assets and Liabilities
In December 2011, FASB issued additional authoritative accounting guidance to improve information disclosed about financial and derivative instruments. The guidance requires an entity to disclose information about offsetting and related arrangements to enable users of the financial statements to understand the effect of those arrangements on its financial position. In January 2013, FASB amended this guidance to limit the scope to derivative instruments, repurchase agreements and reverse repurchase agreements, and securities borrowing and securities lending transactions. The Ameren Companies adopted this guidance for the first quarter of 2013. The implementation of this additional guidance did not affect the Ameren Companies’ results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. See Note 7 – Derivative Financial Instruments for the required additional disclosures.
Presentation of an Unrecognized Tax Benefit
In July 2013, FASB issued additional authoritative accounting guidance to provide clarity for the financial statement presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. It requires entities to present an unrecognized tax benefit as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward to the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is available under the tax law. Currently, any unrecognized tax benefit is recorded in “Other deferred credits and liabilities” on Ameren's, Ameren Missouri's, and Ameren Illinois' balance sheets. After this guidance becomes effective, any unrecognized tax benefit will be recorded in “Accumulated deferred income taxes, net” as a reduction to the deferred tax assets for net operating loss, a similar tax loss, and tax credit carryforwards on the respective balance sheets. At December 31, 2013, unrecognized tax benefits of $48 million and $15 million would have been recorded in “Accumulated deferred income taxes, net” at Ameren and Ameren Missouri, respectively under this new guidance. To the extent that an unrecognized tax benefit exceeds these carryforwards, the excess would continue to be recorded in “Other deferred credits and liabilities” on the respective balance sheets, consistent with current authoritative accounting guidance. The amended guidance will not affect the Ameren Companies' results of operations or liquidity, as this guidance is presentation-related only. This guidance will be effective for the Ameren Companies beginning in the first quarter of 2014.
Asset Retirement Obligations
Authoritative accounting guidance requires us to record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and to capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we are required to make adjustments to AROs based on changes in the estimated fair values of the obligations. Corresponding increases in asset book values are depreciated over the remaining useful life of the related asset. Uncertainties as to the probability, timing, or amount of cash flows associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with Ameren Missouri’s Callaway energy center decommissioning costs, asbestos removal, CCR storage facilities, and river structures. Also, Ameren and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal. In addition, Ameren, Ameren Missouri and Ameren Illinois have recorded AROs for the disposal of certain transformers.
Asset removal costs accrued by our rate-regulated operations that do not constitute legal obligations are classified as a regulatory liability. See Note 2 – Rate and Regulatory Matters.
The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2013, and 2012:
	Ameren				Ameren				Ameren(a)
	Missouri(a)				Illinois(b)
Balance at December 31, 2011	$	328			$	3			$	331
Liabilities incurred	—				—				—
Liabilities settled	(1		)		(c)				(1		)
Accretion in 2012(d)	18				(c)				18
Change in estimates(e)	1				(c)				1
Balance at December 31, 2012	$	346			$	3			$	349
Liabilities incurred	—				—				—
Liabilities settled	(1		)		(c)				(1		)
Accretion in 2013(d)	19				(c)				19
Change in estimates(e)	2				(c)				2
Balance at December 31, 2013	$	366			$	3			$	369
(a)	The nuclear decommissioning trust fund assets of $494 million and $408 million as of December 31, 2013, and 2012, respectively, are restricted for decommissioning of the Callaway energy center.
(b)	Balance included in “Other deferred credits and liabilities” on the balance sheet.
(c)	Less than $1 million.
(d)	Accretion expense was recorded as an increase to regulatory assets at Ameren Missouri and Ameren Illinois.
(e)	Ameren Missouri changed its fair value estimates for asbestos removal in 2012 and 2013, and for certain CCR storage facilities in 2013.
See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the AROs related to the abandoned Meredosia and Hutsonville energy centers, which are presented as discontinued operations and therefore not included in the table above.
Employee Separation Charges
During the fourth quarter of 2011, Ameren Missouri and Ameren Services extended voluntary separation offers consistent with Ameren’s standard management separation program to eligible management and labor union-represented employees. Approximately 340 employees of Ameren Missouri and Ameren Services accepted the offers and left their employment by December 31, 2011. Ameren and Ameren Missouri recorded a pretax charge to earnings of $28 million and $27 million, respectively, for the severance costs related to these offers. These charges were recorded in “Other operations and maintenance" expense in each company’s statement of income for the year ended December 31, 2011. Substantially all of the severance costs were paid in the first quarter of 2012. The severance costs related to participating Ameren Services employees were allocated to affiliates consistent with the terms of its support services agreement, which is described in Note 14 – Related Party Transactions.

Rate_And_Regulatory_Matters

Rate And Regulatory Matters	12 Months Ended
	Dec. 31, 2013
Public Utilities, General Disclosures [Abstract]	'
RATE AND REGULATORY MATTERS	'
	RATE AND REGULATORY MATTERS
	Below is a summary of significant regulatory proceedings and related lawsuits. We are unable to predict the ultimate outcome of these matters, the timing of the final decisions of the various agencies and courts, or the impact on our results of operations, financial position, or liquidity.
	Missouri
	FAC Prudence Review
	In April 2011, the MoPSC issued an order with respect to its review of Ameren Missouri's FAC for the period from March 1, 2009, to September 30, 2009. In this order, the MoPSC ruled that Ameren Missouri should have included in the FAC calculation all revenues and costs associated with certain long-term partial requirements sales that were made by Ameren Missouri because of the loss of Noranda's load caused by a severe ice storm in January 2009. As a result of the order, Ameren Missouri recorded a pretax charge to earnings of $18 million, including $1 million for interest, in 2011 for its obligation to refund to its electric customers the earnings associated with these sales previously recognized by Ameren Missouri during the period from March 1, 2009, to September 30, 2009. In May 2012, upon appeal by Ameren Missouri, the Cole County Circuit Court reversed the MoPSC's April 2011 order. In June 2012, the MoPSC and a group of large industrial customers filed an appeal of the Cole County Circuit Court's ruling to the Missouri Court of Appeals, Western District. In May 2013, the Missouri Court of Appeals upheld the MoPSC’s April 2011 order and reversed the Cole County Circuit Court’s May 2012 decision.
	Ameren Missouri’s FAC calculation for the period from October 1, 2009, to May 31, 2011, excluded all revenues and costs associated with certain long-term partial requirements sales that were made by Ameren Missouri because of the loss of Noranda’s load caused by a severe ice storm in January 2009, similar to the FAC calculation for the period from March 1, 2009, to September 30, 2009. The MoPSC issued an order in July 2013, which was similar to the MoPSC's April 2011 order, as a result of which Ameren Missouri recorded a pretax charge to earnings of $26 million, including $1 million for interest, in 2013 for its estimated obligation to refund to Ameren Missouri’s electric customers the earnings associated with these sales previously recognized by Ameren Missouri for the period from October 1, 2009, to May 31, 2011. Ameren Missouri recorded the charge to “Operating Revenues – Electric” and the related interest to “Interest Charges” with a corresponding offset to “Current regulatory liabilities.” No similar revenues were excluded from FAC calculations after May 2011.
	Separately, in July 2011, Ameren Missouri filed a request with the MoPSC for an accounting authority order that would allow Ameren Missouri to defer fixed costs totaling $36 million that were not previously recovered from Noranda as a result of the loss of load caused by the severe 2009 ice storm for potential recovery in a future electric rate case. In November 2013, the MoPSC issued an order approving Ameren Missouri's request for an accounting authority order. Ameren Missouri will seek to recover these fixed costs in its next electric rate case. In February 2014, MIEC filed an appeal of the accounting authority order to the Missouri Court of Appeals, Western District.
	2012 Electric Rate Order
	In December 2012, the MoPSC issued an order approving an increase for Ameren Missouri in annual revenues for electric service of $260 million. The revenue increase was based on a 9.8% return on equity, a capital structure composed of 52.3% common equity, and a rate base of $6.8 billion. Rate changes consistent with the order became effective on January 2, 2013. In January 2013, Ameren Missouri appealed the order with respect to the amount of property taxes included in the order to the Missouri Court of Appeals, Western District. Later in 2013, Ameren Missouri withdrew this appeal. In February 2013, the MoOPC, MIEC, and other parties filed separate appeals to the Missouri Court of Appeals, Western District, relating to the order's treatment of transmission costs in the FAC. In October 2013, the Missouri Court of Appeals, Western District, upheld the order. MoOPC, MIEC, and other parties filed a request to transfer their appeal to the Missouri Supreme Court, which was subsequently denied.
	MEEIA Order
	The MoPSC's December 2012 electric rate order approved Ameren Missouri's implementation of MEEIA megawatthour savings targets, energy efficiency programs, and associated cost recovery mechanisms and incentive awards. A MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the projected amounts collected from customers for the MEEIA program costs and its projected lost revenues.
	In addition to the program costs and lost revenues discussed above, the terms of Ameren Missouri's MoPSC-approved MEEIA programs offer an incentive award that would allow Ameren Missouri to earn additional revenues by achieving certain energy efficiency goals, including approximately $19 million if 100% of its energy efficiency goals are achieved during the three-year period, with the potential to earn more if Ameren Missouri's energy savings exceed those goals. Ameren Missouri must achieve at least 70% of its energy efficiency goals before it earns any incentive award. The recovery of an incentive award from customers, if the energy efficiency goals are achieved, is expected in 2017 through the above-mentioned rider.
	Rate Design and Earnings Complaint Cases
	On February 13, 2014, Ameren Missouri’s largest customer, Noranda, and 37 residential customers filed an earnings complaint case and a rate design complaint case with the MoPSC. In the earnings complaint case, Noranda and the residential customers asserted that Ameren Missouri’s electric delivery service business is earning more than the 9.8% return on equity authorized in the MoPSC's December 2012 electric rate order and requested the MoPSC to approve a reduction of the authorized return on equity to 9.4%. The rate design complaint case seeks to reduce Noranda’s electricity cost with an offsetting increase in electricity cost for Ameren Missouri’s other customers. The rate design complaint case asks the MoPSC to expedite its decision and grant relief by August 1, 2014.
	The MoPSC has ordered Ameren Missouri to file a response to these two complaints by March 17, 2014. The MoPSC has no time requirement by which it must issue an order in these cases. Ameren Missouri opposes both requests filed by Noranda and the residential customers and will vigorously defend itself.
	Illinois
	IEIMA
	Under the provisions of the IEIMA, Ameren Illinois' electric delivery service rates effective for customers' billings in 2013 were subject to an annual revenue requirement reconciliation to its actual 2013 costs. The 2013 revenue requirement reconciliation will be filed with the ICC in 2014. The approved annual revenue requirement reconciliation adjustment relating to 2013 will be reflected in customer rates beginning in January 2015. Throughout the year, Ameren Illinois records a regulatory asset or a regulatory liability and a corresponding increase or decrease to operating revenues for any differences between the revenue requirement in effect for that year and its estimate of the probable increase or decrease in the revenue requirement expected to ultimately be approved by the ICC based on that year's actual costs incurred. As of December 31, 2013, Ameren Illinois recorded a $65 million regulatory asset to reflect its expected 2013 revenue requirement reconciliation adjustment, which will be recovered from customers in 2015. Ameren Illinois also recorded a regulatory liability of $65 million and $55 million as of December 31, 2013, and December 31, 2012, respectively, to reflect its 2012 revenue requirement reconciliation adjustment, with interest, which will be refunded to customers in 2014.
	In May 2013, Illinois enacted into law certain amendments to the IEIMA that modified its implementation. The law clarified that the IEIMA requires that the year-end rate base must be used to calculate the revenue requirement reconciliation and that the interest applied to the revenue requirement reconciliation and return on equity collar adjustments must be equal to a company's weighted-average return calculated under the formula rate.
	In September 2012, the ICC issued an order in Ameren Illinois' initial filing under the IEIMA's performance-based formula rate framework, which Ameren Illinois appealed to the Appellate Court of the Fourth District of Illinois. In December 2012, the ICC issued an order in Ameren Illinois' update filing approving an Ameren Illinois electric delivery service revenue requirement of $765 million, based on 2011 recoverable costs and expected net plant additions in 2012. The delivery service rates became effective on January 1, 2013. In January 2013, Ameren Illinois filed an appeal of the ICC's update filing order to the Appellate Court of the Fourth District of Illinois. Both orders were consolidated for appeal with the primary issues being the treatment of accumulated deferred income taxes and vacation obligations as well as the calculation of Ameren Illinois' capital structure. In December 2013, the appellate court rendered its decision upholding the ICC's September and December 2012 orders. Ameren Illinois expects to file an appeal to the Illinois Supreme Court in March 2014.
	In December 2013, the ICC issued an order in Ameren Illinois' annual update filing, which was based on 2012 recoverable costs and expected net plant additions for 2013, approving an Ameren Illinois electric delivery service revenue requirement of $788 million, before consideration of the 2012 revenue requirement reconciliation refund. The ICC order resulted in a net $45 million decrease in Ameren Illinois' electric delivery service revenue requirement. The calculation included a refund to customers of the 2012 revenue requirement reconciliation of $68 million, which included an estimate for interest through the end of 2014. However, this refund is partially offset by an annual revenue requirement increase of $23 million primarily due to higher recoverable costs in 2012 compared to 2011. The ICC order establishes rates for all of 2014. In January 2014, Ameren Illinois filed a request for rehearing with the ICC regarding the electric delivery service rate order, which the ICC denied. In February 2014, Ameren Illinois filed an appeal with the Appellate Court of the Fourth District of Illinois regarding the calculation of its capital structure and the treatment of accumulated deferred income taxes related to the transfer of former Ameren Missouri assets in Illinois to Ameren Illinois.
	In the December 2013 order, the ICC disallowed, in part, the recovery from customers of the debt premium costs paid by Ameren Illinois for a tender offer in August 2012 to repurchase outstanding senior secured notes. At the time of the tender offer, Ameren Illinois recorded this loss on the reacquired debt as a regulatory asset. As a result of the ICC order, Ameren and Ameren Illinois each recorded in 2013 a pretax charge to earnings of $15 million relating to the partial disallowance of the premium costs. This charge was recorded in the statement of income for Ameren and Ameren Illinois as “Interest charges” with a corresponding decrease to “Regulatory assets.”
	2013 Natural Gas Delivery Service Rate Order
	In December 2013, the ICC issued a rate order that approved an increase in revenues for natural gas delivery service of $32 million. The revenue increase was based on a 9.1% return on equity, a capital structure composed of 51.7% common equity, and a rate base of $1.1 billion. The rate order was based on a 2014 future test year. The rate changes became effective January 1, 2014. In January 2014, Ameren Illinois filed a request for rehearing with the ICC regarding the natural gas delivery service rate order, which the ICC denied. Ameren Illinois expects to file an appeal of the ICC's order in March 2014.
	Similar to the December 2013 electric rate order discussed above, this natural gas rate order included a partial disallowance relating to the August 2012 costs for the tender offer to repurchase outstanding senior secured notes. The pretax loss of $15 million discussed above includes the impact of both the December 2013 ICC electric and natural gas delivery service rate orders.
	Natural Gas Consumer, Safety and Reliability Act
	In July 2013, Illinois enacted the Natural Gas Consumer, Safety and Reliability Act, which encourages Illinois natural gas utilities to accelerate modernization of the state’s natural gas infrastructure and provides additional ICC oversight of natural gas utility performance. The law allows natural gas utilities the option to file for, and requires the ICC to approve, a rate rider mechanism to recover costs of certain natural gas infrastructure investments made between rate cases. The law does not require a minimum level of investment. Ameren Illinois expects to begin including investments under this regulatory framework in 2015. Ameren Illinois' decision to accelerate modernization of its natural gas infrastructure under this regulatory framework is dependent upon multiple considerations, including the allowed return on equity under this framework compared with other Ameren and Ameren Illinois investment options.
	ATXI Transmission Project
	ATXI's Illinois Rivers project is a MISO-approved project to build a 345-kilovolt line from western Indiana across the state of Illinois to eastern Missouri at an estimated cost of $1.1 billion. In August 2013, the ICC granted a certificate of public convenience and necessity and approved seven of a total of nine sections of the route and three of the proposed nine substations for the Illinois Rivers project. The ICC order indicated the project is necessary to address transmission and reliability needs in an efficient and equitable manner and that the project will benefit the development of a competitive electricity market. The order also indicated that ATXI is capable of constructing, managing and financing the project. In October 2013, the ICC granted ATXI's request for a rehearing to consider additional evidence regarding the two segments of the route and six substations that were not approved, as well as the requests for rehearing of certain other parties regarding two of the approved segments of the route. In February 2014, the ICC issued a final order on rehearing approving the remaining substations and routes for the Illinois Rivers project.
	Federal
	2011 Wholesale Distribution Rate Case
	In January 2011, Ameren Illinois filed a request with FERC to increase its annual revenues for electric delivery service for its wholesale customers. These wholesale distribution revenues are treated as a deduction from Ameren Illinois' revenue requirement in retail rate filings with the ICC. In March 2011, FERC issued an order authorizing the proposed rates to take effect, subject to refund when the final rates are determined. Ameren Illinois reached an agreement with four of its nine wholesale customers. FERC has approved these settlement agreements, and any refund obligations related thereto have been made. The impasse with the remaining five wholesale customers has resulted in FERC litigation. In November 2012, a FERC administrative law judge issued an initial decision, which is now pending before FERC. The timing of a FERC decision is uncertain. In accordance with the administrative law judge's initial decision, Ameren and Ameren Illinois have both included on their balance sheets in "Current regulatory liabilities" an estimate of $13 million and $8 million as of December 31, 2013, and December 31, 2012, respectively, for the refund due to wholesale customers relating to billings for the period from March 2011 through December 2013.
	Ameren Illinois Electric Transmission Rate Refund
	In July 2012, FERC issued an order concluding that Ameren Illinois improperly included acquisition premiums, primarily goodwill, in determining the common equity used in its electric transmission formula rate, and thereby inappropriately recovered a higher amount from its electric transmission customers. The order required Ameren Illinois to make refunds to customers for such improperly included amounts. In August 2012, Ameren Illinois filed a request for a rehearing of this order. It is unknown when FERC will rule on Ameren's rehearing request, as it is under no deadline to do so.
	Ameren Illinois submitted a refund report in November 2012 and concluded that no refund was warranted. Several wholesale customers filed a protest with FERC regarding Ameren's conclusion that no refund was warranted. In June 2013, FERC issued an order that rejected Ameren Illinois' November 2012 refund report and provided guidance as to the filing of a new refund report. In July 2013, Ameren Illinois filed a revised refund report based on the guidance provided in the June 2013 order, as well as a request for a rehearing of that order. Ameren Illinois' July 2013 refund report also concluded that no refund was warranted. Ameren Illinois estimated the maximum pretax charge to earnings for this possible refund obligation through December 31, 2013, would be $15 million, before interest charges. If Ameren Illinois were to determine that a refund to its electric transmission customers is probable, a charge to earnings would be recorded for the refund in the period in which that determination was made.
	FERC Complaint Case
	In November 2013, a customer group filed a complaint case with FERC seeking a reduction in the allowed return on common equity, as well as a limit on the common equity ratio, under the MISO tariff. Currently, the FERC-allowed return on common equity for MISO transmission owners is 12.38%. This complaint case could result in a reduction to Ameren Illinois' and ATXI's allowed return on common equity. That reduction could also result in a refund for transmission service revenues earned after the filing of the complaint case in November 2013. FERC has not issued an order in this case, and it is under no deadline to do so. Ameren is not able to predict when or how FERC will rule on this complaint case.
	Ameren Missouri Power Purchase Agreement with Entergy
	Beginning in 2005, FERC issued a series of orders addressing a complaint filed in 2001 by the Louisiana Public Service Commission (LPSC) against Entergy and certain of its affiliates. The complaint alleged unjust and unreasonable cost allocations. As a result of the FERC orders, Entergy began billing Ameren Missouri in 2007 for additional charges under a 165-megawatt power purchase agreement, which expired August 31, 2009. In May 2012, FERC issued an order stating that Entergy should not have included additional charges to Ameren Missouri under the power purchase agreement. Pursuant to the order, in June 2012, Entergy paid Ameren Missouri $31 million, with $24 million recorded as a reduction to “Purchased power” expense and $5 million for interest recorded as “Miscellaneous income” in the statement of income. The remaining $2 million was recorded as an offset to the FAC under-recovered regulatory asset for the amount refundable to customers. The amount of the Entergy refund recorded to the FAC regulatory asset related to the period when the FAC was effective; therefore, such costs were previously included in customer rates. In July 2012, Entergy filed an appeal of FERC's January 2010 and May 2012 orders to the United States Court of Appeals for the District of Columbia Circuit, which was subsequently dismissed on a procedural issue. In November 2013, Entergy refiled the appeal of FERC's May 2012 order with the United States Court of Appeals for the District of Columbia Circuit. Ameren is not able to predict when or how the court will rule on Entergy's appeal.
	The LPSC appealed FERC’s orders regarding LPSC’s complaint against Entergy Services, Inc. to the United States Court of Appeals for the District of Columbia Circuit. In April 2008, that court ordered further FERC proceedings regarding LPSC’s complaint. The court ordered FERC to explain its previous denial of retroactive refunds and the implementation of prospective charges. FERC’s decision on remand of the retroactive impact of these issues could have a financial impact on Ameren Missouri. Ameren Missouri is unable to predict when or how FERC will respond to the court’s decisions. Ameren Missouri estimates that it could incur an additional expense of up to $25 million if FERC orders retroactive application for the years 2001 to 2005. Ameren Missouri believes that the likelihood of incurring any expense is not probable, and therefore no liability has been recorded as of December 31, 2013.
	Combined Construction and Operating License
	In 2008, Ameren Missouri filed an application with the NRC for a COL for a new nuclear unit at Ameren Missouri's existing Callaway County, Missouri, energy center site. In 2009, Ameren Missouri suspended its efforts to build a new nuclear unit at its existing Missouri nuclear energy center site, and the NRC suspended review of the COL application.
	In March 2012, the DOE announced the availability of investment funds for the design, engineering, manufacturing, and sale of American-made small modular nuclear reactors. In April 2012, Ameren Missouri entered into an exclusive agreement to support Westinghouse's application for the first installment of DOE's small modular nuclear reactor investment funds. The DOE investment funding is intended to support engineering and design certifications and a COL for up to two small modular reactor designs over five years. A COL is issued by the NRC to permit construction and operation of a nuclear energy center at a specific site in accordance with established laws and regulations. Obtaining a COL from the NRC would not obligate Ameren Missouri to build a small modular reactor at the Callaway site; however, it would preserve the option to move forward in a timely fashion should conditions be right to build a small modular reactor in the future. A COL is valid for at least 40 years. In November 2012, the DOE awarded the first installment of investment funds for only one small modular reactor design, which was not the Westinghouse design. The DOE stated that a second installment of investment funds would be awarded during 2013. In December 2013, the DOE did not award Westinghouse the second installment of investment funds. Ameren Missouri's agreement to exclusively support Westinghouse's application expired in January 2014.
	Ameren Missouri estimated the total cost that would be required to obtain the small modular reactor COL to be $80 million to $100 million. As of December 31, 2013, Ameren Missouri had capitalized investments of $69 million for the development of a new nuclear energy center. Ameren is currently evaluating all potential nuclear technologies in order to maintain an option for nuclear power in the future.
	All of Ameren Missouri's capitalized investments for the development of a new nuclear energy center will remain capitalized while management pursues options to maximize the value of its investment. If efforts to license additional nuclear generation are abandoned or management concludes it is probable the costs incurred will be disallowed in rates, a charge to earnings would be recognized in the period in which that determination is made.
	Pumped-storage Hydroelectric Energy Center Relicensing
	In June 2008, Ameren Missouri filed a relicensing application with FERC to operate its Taum Sauk pumped-storage hydroelectric energy center for another 40 years. The existing FERC license expired on June 30, 2010. In July 2010, Ameren Missouri received a license extension that allows Taum Sauk to continue operations until FERC issues a new license. A FERC order is expected in 2014. Ameren Missouri cannot predict the ultimate outcome of FERC's review of the application.
	Regulatory Assets and Liabilities
	In accordance with authoritative accounting guidance regarding accounting for the effects of certain types of regulation, Ameren Missouri and Ameren Illinois defer certain costs as regulatory assets pursuant to actions of regulators or based on the expected ability to recover such costs in rates charged to customers. Ameren Missouri and Ameren Illinois also defer certain amounts as regulatory liabilities because of actions of regulators or because of the expectation that such amounts will be returned to customers in future rates. The following table presents Ameren’s, Ameren Missouri’s and Ameren Illinois’ regulatory assets and regulatory liabilities at December 31, 2013, and 2012:
			2013						2012
			Ameren		Ameren		Ameren			Ameren		Ameren		Ameren
			Missouri		Illinois					Missouri		Illinois
	Current regulatory assets:
	Under-recovered FAC(a)(b)		$	104	$	—	$	104		$	145	$	—	$	145
	Under-recovered Illinois electric power costs(c)		—		1		1			—		—		—
	Under-recovered PGA(c)		—		1		1			5		7		12
	MTM derivative losses(d)		14		36		50			13		77		90
	Total current regulatory assets		$	118	$	38	$	156		$	163	$	84	$	247
	Noncurrent regulatory assets:
	Pension and postretirement benefit costs(e)		$	44	$	140	$	184		$	348	$	424	$	772
	Income taxes(f)		230		7		237			231		4		235
	Asset retirement obligations(g)		—		5		5			—		5		5
	Callaway costs(a)(h)		40		—		40			44		—		44
Unamortized loss on reacquired debt(a)(i)		77		74		151			81		100		181
Recoverable costs – contaminated facilities(j)		—		271		271			—		248		248
MTM derivative losses(d)		8		118		126			7		128		135
Storm costs(k)		5		3		8			9		—		9
Demand-side costs before MEEIA implementation(a)(l)		58		—		58			73		—		73
Reserve for workers’ compensation liabilities(m)		6		6		12			6		6		12
Credit facilities fees(n)		5		—		5			6		—		6
Common stock issuance costs(o)		4		—		4			7		—		7
Construction accounting for pollution control equipment(a)(p)		22		—		22			23		—		23
Solar rebate program(a)(q)		27		—		27			5		—		5
IEIMA revenue requirement reconciliation(r)		—		65		65			—		—		—
Other(s)(t)		8		12		25			12		19		31
Total noncurrent regulatory assets		$	534	$	701	$	1,240		$	852	$	934	$	1,786
Current regulatory liabilities:
Over-recovered FAC(b)		$	26	$	—	$	26		$	—	$	—	$	—
Over-recovered Illinois electric power costs(c)		—		51		51			—		58		58
Over-recovered PGA(c)		5		29		34			—		15		15
MTM derivative gains(d)		26		1		27			18		1		19
Wholesale distribution refund(u)		—		13		13			—		8		8
IEIMA revenue requirement reconciliation(r)		—		65		65			—		—		—
Total current regulatory liabilities		$	57	$	159	$	216		$	18	$	82	$	100
Noncurrent regulatory liabilities:
Income taxes(v)		$	38	$	3	$	41		$	42	$	4	$	46
Removal costs(w)		828		610		1,438			766		581		1,347
Asset retirement obligation(g)		146		—		146			80		—		80
MTM derivative gains(d)		1		—		1			2		—		2
Bad debt riders(x)		—		8		8			—		12		12
Pension and postretirement benefit costs tracker(y)		15		—		15			23		—		23
Energy efficiency riders(z)		3		33		36			—		20		20
IEIMA revenue requirement reconciliation(r)		—		—		—			—		55		55
FERC transmission revenue requirement reconciliation(aa)		—		10		10			—		—		—
Other(ab)		10		—		10			4		—		4
Total noncurrent regulatory liabilities		$	1,041	$	664	$	1,705		$	917	$	672	$	1,589
(a)	These assets earn a return.
(b)	Under-recovered or over-recovered fuel costs to be recovered through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from customers that occurs over the next eight months.
(c)	Costs under- or over-recovered from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.
(d)	Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.
(e)	These costs are being amortized in proportion to the recognition of prior service costs (credits), transition obligations (assets), and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 11 – Retirement Benefits for additional information.
(f)	Offset to certain deferred tax liabilities for expected recovery of future income taxes when paid. This will be recovered over the expected life of the related assets.
(g)	Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.
(h)	Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the remaining life of the energy center's current operating license, which expires in 2024.
(i)	Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.
(j)	The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 15 – Commitments and Contingencies for additional information.
(k)	Actual storm costs in a test year that exceed the MoPSC staff’s normalized storm costs for rate purposes. As approved by the December 2012 MoPSC electric rate order, the 2006, 2007, and 2008 storm costs are being amortized through December 2014. As approved by the May 2010 MoPSC electric rate order, the 2009 storm costs are being amortized through June 2015. The Ameren Illinois total includes 2013 storm costs deferred in accordance with the IEIMA. These costs are being amortized over a five-year period beginning in 2013.
(l)	Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized over a six-year period that began in July 2010. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013.
(m)	Reserve for workers’ compensation claims. The period of recovery will depend on the timing of actual expenditures.
(n)	Ameren Missouri’s costs incurred to enter into and maintain the 2012 Ameren Missouri Credit Agreement. These costs are being amortized over five years, beginning in November 2012. These costs are being amortized to construction work in progress, which will be depreciated when assets are placed into service.
(o)	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to recover its portion of Ameren’s September 2009 common stock issuance costs. These costs are being amortized over five years, beginning in July 2010.
(p)	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment could be included in customer rates. These costs will be amortized over the expected life of the Sioux energy center, which is currently through 2033.
(q)	Costs associated with Ameren Missouri's solar rebate program beginning in August 2012 to fulfill Ameren Missouri's renewable energy portfolio requirement. The amortization period for these costs will be three years, commencing with the next Ameren Missouri electric rate case order.
(r)	The asset balance relates to the difference between Ameren Illinois' 2013 revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework, and the revenue requirement included in customer rates for 2013. Subject to ICC approval, this asset will be collected from customers in 2015. The liability balance relates to the difference between Ameren Illinois' 2012 revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for 2012. This liability will be refunded to customers in 2014.
(s)	The Ameren Illinois total includes Ameren Illinois Merger integration and optimization costs, which are amortized over four years, beginning in January 2012. The Ameren Illinois total also includes costs related to the 2013 natural gas delivery service rate case costs, which are being amortized over a two-year period that began in January 2014. The Ameren Illinois total also includes a portion of the unamortized debt fair value adjustment recorded upon Ameren's acquisition of IP. This portion is being amortized over the remaining life of the related debt. At Ameren Missouri, the balance primarily includes the cost of renewable energy credits to fulfill its renewable energy portfolio requirement. Costs incurred from January 2010 through July 2012 are being amortized over three years, beginning in January 2013.
(t)	The Ameren total includes $5 million for ATXI's revenue requirement reconciliation adjustments for 2012 and 2013 calculated pursuant to the FERC's electric transmission formula ratemaking framework. These adjustments will be collected from customers in 2014 for the 2012 revenue requirement reconciliation and in 2015 for the 2013 revenue requirement reconciliation.
(u)	Estimated refund to wholesale electric customers. See 2011 Wholesale Distribution Rate Case above.
(v)	Unamortized portion of investment tax credits, federal excess deferred taxes, and uncertain tax position tracker. The tracker is being amortized over three years, beginning in January 2013. The unamortized portion of investment tax credit is being amortized over the expected life of the underlying assets.
(w)	Estimated funds collected for the eventual dismantling and removal of plant from service, net of salvage value, upon retirement related to our rate-regulated operations.
(x)	A regulatory tracking mechanism for the difference between the level of bad debt expense incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2011 was refunded to customers from June 2012 through May 2013. The over-recovery relating to 2012 is being refunded to customers from June 2013 through May 2014. The over-recovery relating to 2013 will be refunded to customers from June 2013 through May 2014.
(y)	A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs built into rates. For periods prior to August 2012, the MoPSC's December 2012 electric rate order directed the amortization to occur over five years, beginning in January 2013. For periods after August 2012, the amortization period will be determined in a future Ameren Missouri electric rate case.
(z)	The Ameren Illinois balance relates its regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. This over-recovery will be refunded to customers over the following 12 months after the plan year. The Ameren Missouri balance relates to its MEEIA program costs incurred and projected lost revenues compared to the amount previously collected from customers. Beginning in January 2014, a MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the projected amounts collected from customers for the MEEIA program costs and its projected lost revenues. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs and projected lost revenues are incurred.
(aa)	Ameren Illinois' 2013 revenue requirement reconciliation adjustment calculated pursuant to the FERC's electric transmission formula ratemaking framework. This liability will be refunded to customers in 2015.
(ab)	Balance primarily includes the costs of renewable energy credits to fulfill Ameren Missouri's renewable energy portfolio requirement from August 2012 through December 2013, which were less than the amount included in rates. The amortization period for this over-recovery will be determined in a future Ameren Missouri electric rate case.
Ameren Missouri and Ameren Illinois continually assess the recoverability of their regulatory assets. Under current accounting standards, regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that payments of regulatory liabilities are no longer probable, the amounts are credited to earnings.

Property_And_Plant_Net

Property And Plant, Net	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
PROPERTY AND PLANT, NET	'
	PROPERTY AND PLANT, NET
	The following table presents property and plant, net, for each of the Ameren Companies at December 31, 2013, and 2012:
			Ameren			Ameren			Other		Ameren(a)(b)
			Missouri(a)			Illinois
	2013
	Property and plant, at original cost:
	Electric		$	15,964		$	5,426		$	336	$	21,726
	Natural gas		413			1,562			—		1,975
			16,377			6,988			336		23,701
	Less: Accumulated depreciation and amortization		6,766			1,627			251		8,644
			9,611			5,361			85		15,057
	Construction work in progress:
	Nuclear fuel in process		246			—			—		246
	Other		595			228			79		902
	Property and plant, net		$	10,452		$	5,589		$	164	$	16,205
	2012
	Property and plant, at original cost:
	Electric		$	15,638		$	4,985		$	319	$	20,942
	Natural gas		393			1,461			—		1,854
			16,031			6,446			319		22,796
	Less: Accumulated depreciation and amortization		6,614			1,495			237		8,346
			9,417			4,951			82		14,450
	Construction work in progress:
	Nuclear fuel in process		317			—			—		317
	Other		427			101			53		581
	Property and plant, net		$	10,161		$	5,052		$	135	$	15,348
	(a)	Amounts in Ameren and Ameren Missouri include two electric generation CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $228 million at December 31, 2013, and $228 million at December 31, 2012. The total accumulated depreciation associated with the two CTs was $56 million and $52 million at December 31, 2013, and 2012, respectively. In addition, Ameren Missouri has investments in debt securities, which were classified as held-to-maturity, related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2013, and 2012, the carrying value of these debt securities was $299 million and $304 million, respectively.
	(b)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
	The following table provides accrued capital and nuclear fuel expenditures at December 31, 2013, 2012, and 2011, which represent noncash investing activity excluded from the accompanying statements of cash flows:
		Ameren(a)			Ameren			Ameren
					Missouri			Illinois
	Accrued capital expenditures:
	2013	$	175		$	74		$	86
	2012	107			63			37
	2011	97			73			18
	Accrued nuclear fuel expenditures:
	2013	8			8			(b)
	2012	8			8			(b)
	2011	36			36			(b)
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
	(b)	Not applicable.

ShortTerm_Debt_And_Liquidity

Short-Term Debt And Liquidity	12 Months Ended
	Dec. 31, 2013
Line of Credit Facility [Abstract]	'
SHORT-TERM DEBT AND LIQUIDITY	'
	SHORT-TERM DEBT AND LIQUIDITY
	The liquidity needs of the Ameren Companies are typically supported through the use of available cash, short-term intercompany borrowings, drawings under committed bank credit agreements, or commercial paper issuances.
	2012 Credit Agreements
	On November 14, 2012, Ameren and Ameren Missouri entered into the $1 billion 2012 Missouri Credit Agreement. The 2010 Missouri Credit Agreement was terminated when the 2012 Missouri Credit Agreement when into effect. Also on November 14, 2012, Ameren and Ameren Illinois entered into the $1.1 billion 2012 Illinois Credit Agreement. The 2010 Illinois Credit Agreement was terminated when the 2012 Illinois Credit Agreement went into effect. These facilities cumulatively provide $2.1 billion of credit through November 14, 2017, which may be extended with the agreement of the lenders, subject to the terms of such agreements, for two additional one-year periods. The facilities currently include 24 international, national, and regional lenders, with no lender providing more than $125 million of credit in aggregate.
	The obligations of each borrower under the respective 2012 Credit Agreements to which it is a party are several and not joint, and, except under limited circumstances relating to expenses and indemnities, the obligations of Ameren Missouri and Ameren Illinois under the respective 2012 Credit Agreements are not guaranteed by Ameren or any other subsidiary of Ameren. The maximum aggregate amount available to each borrower under each facility is shown in the following table (such amount being such borrower's "Borrowing Sublimit"):
			2012 Missouri Credit Agreement		2012 Illinois
					Credit Agreement
	Ameren	$	500		$	300
	Ameren Missouri		800		(a)
	Ameren Illinois		(a)		800
	(a)	Not applicable.
	Ameren has the option to seek additional commitments from existing or new lenders to increase the total facility size of the 2012 Credit Agreements up to a maximum amount of $1.2 billion for the 2012 Missouri Credit Agreement and $1.3 billion for the 2012 Illinois Credit Agreement. The 2012 Credit Agreements, as well as the Borrowing Sublimits of Ameren and Ameren Missouri, will mature and expire on November 14, 2017. The Borrowing Sublimit of Ameren Illinois will mature and expire on September 30, 2014, subject to extension on a 364-day basis or for a longer period upon notice by the borrower of receipt of any and all required federal or state regulatory approvals, as permitted under the credit agreement, but in no event later than November 14, 2017. In October 2013, Ameren Illinois filed a petition seeking state regulatory approval necessary to extend the maturity date of its Borrowing Sublimit under the 2012 Illinois Credit Agreement to November 14, 2017. If and when regulatory approval is received, no lender approval will be required to effect the extension. The principal amount of each revolving loan owed by a borrower under any of the 2012 Credit Agreements to which it is a party will be due and payable no later than the final maturity date relating to such borrower under such 2012 Credit Agreements.
	The obligations of all borrowers under the 2012 Credit Agreements are unsecured. Loans are available on a revolving basis under each of the 2012 Credit Agreements. Funds borrowed may be repaid and, subject to satisfaction of the conditions to borrowing, reborrowed from time to time. At the election of each borrower, the interest rates on such loans will be the alternate base rate ("ABR") plus the margin applicable to the particular borrower and/or the Eurodollar rate plus the margin applicable to the particular borrower. The applicable margins will be determined by the borrower's long-term unsecured credit ratings or, if no such ratings are then in effect, the borrower's corporate/issuer ratings then in effect. Letters of credit in an aggregate undrawn face amount not to exceed 25% of the applicable aggregate commitment under the respective 2012 Credit Agreements are also available for issuance for the account of the borrowers thereunder (but within the $2.1 billion overall combined facility borrowing limitations of the 2012 Credit Agreements).
	The borrowers will use the proceeds from any borrowings under the 2012 Credit Agreements for general corporate purposes, including working capital, commercial paper liquidity support, loan funding under the Ameren money pool arrangements or other short-term intercompany loan arrangements, or paying fees and expenses incurred in connection with the 2012 Credit Agreements.
	The 2012 Credit Agreements are used to borrow cash, to issue letters of credit, and to support issuances under Ameren's $500 million commercial paper program and Ameren Missouri's $500 million commercial paper program. Either of the 2012 Credit Agreements are available to Ameren to support issuances under Ameren's commercial paper program, subject to borrowing sublimits. The 2012 Missouri Credit Agreement is available to support issuances under Ameren Missouri's commercial paper program. Ameren Illinois' $500 million commercial paper program, under which no commercial paper was ever issued, was terminated in 2013. As of December 31, 2013, based on commercial paper outstanding and letters of credit issued under the 2012 Credit Agreements, the aggregate amount of credit capacity available to Ameren (parent), Ameren Missouri and Ameren Illinois, collectively, at December 31, 2013, was $1.7 billion.
	Ameren, Ameren Missouri, and Ameren Illinois did not borrow under the 2012 Credit Agreements for the years ended December 31, 2013, and 2012.
	Commercial Paper
	The following table summarizes the borrowing activity and relevant interest rates under Ameren's commercial paper program, for the years ended December 31, 2013, and 2012:
			2013				2012
	Average daily borrowings outstanding		$	54			$	49
	Outstanding borrowings at period-end		368				—
	Weighted-average interest rate		0.56		%		0.92		%
	Peak borrowings during period		$	368			$	229
	Peak interest rate		0.85		%		1.25		%
	Indebtedness Provisions and Other Covenants
	The information below presents a summary of the Ameren Companies’ compliance with indebtedness provisions and other covenants.
	The 2012 Credit Agreements contain conditions to borrowings and issuances of letters of credit, including the absence of default or unmatured default, material accuracy of representations and warranties (excluding any representation after the closing date as to the absence of material adverse change and material litigation, and the absence of any notice of violation, liability or requirement under any environmental laws that could have a material adverse effect), and obtaining required regulatory authorizations. In addition, as it relates to borrowings under the 2012 Illinois Credit Agreement, it is a condition for any such borrowing that, at the time of and after giving effect to such borrowing, the borrower not be in violation of any limitation on its ability to incur unsecured indebtedness contained in its articles of incorporation.
	The 2012 Credit Agreements also contain nonfinancial covenants, including restrictions on the ability to incur liens, to transact with affiliates, to dispose of assets, to make investments in or transfer assets to its affiliates, and to merge with other entities. The 2012 Credit Agreements require each of Ameren, Ameren Missouri and Ameren Illinois to maintain consolidated indebtedness of not more than 65% of its consolidated total capitalization pursuant to a defined calculation set forth in the agreements. As of December 31, 2013, the ratios of consolidated indebtedness to total consolidated capitalization, calculated in accordance with the provisions of the 2012 Credit Agreements, were 48%, 47% and 44%, for Ameren, Ameren Missouri and Ameren Illinois, respectively. In addition, under the 2012 Illinois Credit Agreement and, by virtue of the cross-default provisions of the 2012 Missouri Credit Agreement, Ameren is required to maintain a ratio of consolidated funds from operations plus interest expense to consolidated interest expense of 2.0 to 1.0, to be calculated quarterly, as of the end of the most recent four fiscal quarters then ending, in accordance with the 2012 Illinois Credit Agreement. Ameren’s ratio as of December 31, 2013, was 5.3 to 1.0. Failure of a borrower to satisfy a financial covenant constitutes an immediate default under the applicable 2012 Credit Agreement.
	The 2012 Credit Agreements contain default provisions that apply separately to each borrower, provided, however, that a default of Ameren Missouri or Ameren Illinois under the applicable 2012 Credit Agreement will also be deemed to constitute a default of Ameren under such agreement. Defaults include a cross-default to a default of such borrower under any other agreement covering outstanding indebtedness of such borrower and certain subsidiaries (other than project finance subsidiaries and nonmaterial subsidiaries) in excess of $50 million in the aggregate (including under the other 2012 Credit Agreement). However, under the default provisions of the 2012 Credit Agreements, any default of Ameren under any such 2012 Credit Agreements that results solely from a default of Ameren Missouri or Ameren Illinois thereunder does not result in a cross-default of Ameren under the other 2012 Credit Agreement. Further, the 2012 Credit Agreement default provisions provide that an Ameren default under any of the 2012 Credit Agreements does not trigger a default by Ameren Missouri or Ameren Illinois.
	None of the Ameren Companies' credit agreements or financing arrangements contain credit rating triggers that would cause a default or acceleration of repayment of outstanding balances. Management believes that the Ameren Companies were in compliance with the provisions and covenants of their credit agreements at December 31, 2013.
	Money Pools
	Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. Ameren Services is responsible for the operation and administration of the money pool agreements.
	Ameren Missouri, Ameren Illinois, and Ameren Services may participate in the utility money pool as both lenders and borrowers. Ameren may participate in the money pool only as a lender. Internal funds are surplus funds contributed to the money pool from participants. The primary sources of external funds for the money pool are the 2012 Credit Agreements and the commercial paper programs. The total amount available to the pool participants from the money pool at any given time is reduced by the amount of borrowings made by participants, but it is increased to the extent that the pool participants advance surplus funds to the money pool or remit funds from other external sources. The availability of funds is also determined by funding requirement limits established by regulatory authorizations. The money pool was established to coordinate and to provide short-term cash and working capital for the participants. Participants receiving a loan under the money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the money pool. The average interest rate for borrowing under the money pool for the year ended December 31, 2013, was 0.14% (2012 - 0.13%).
	See Note 14 – Related Party Transactions for the amount of interest income and expense from the money pool arrangements recorded by the Ameren Companies for the years ended December 31, 2013, 2012, and 2011.
	Unilateral Borrowing Agreement
	In addition, a unilateral borrowing agreement exists among Ameren, Ameren Illinois, and Ameren Services, which enables Ameren Illinois to make short-term borrowings directly from Ameren. The aggregate amount of borrowings outstanding at any time by Ameren Illinois under the unilateral borrowing agreement and the utility money pool agreement, together with any outstanding Ameren Illinois external credit facility borrowings, may not exceed $500 million, pursuant to authorization from the ICC. Ameren Illinois is not currently borrowing under the unilateral borrowing agreement.

LongTerm_Debt_And_Equity_Finan

Long-Term Debt And Equity Financings	12 Months Ended
	Dec. 31, 2013
Long-Term Debt And Equity Financings [Abstract]	'
LONG-TERM DEBT AND EQUITY FINANCINGS	'
	LONG-TERM DEBT AND EQUITY FINANCINGS
	The following table presents long-term debt outstanding, including maturities due within one year, for the Ameren Companies as of December 31, 2013, and 2012:
		2013				2012
	Ameren (Parent):
	8.875% Senior unsecured notes due 2014	$	425			$	425
	Less: Unamortized discount and premium	—				(1		)
	Less: Maturities due within one year	(425		)		—
	Long-term debt, net	$	—			$	424
	Ameren Missouri:
	Senior secured notes:(a)
	4.65% Senior secured notes due 2013	—				200
	5.50% Senior secured notes due 2014	104				104
	4.75% Senior secured notes due 2015	114				114
	5.40% Senior secured notes due 2016	260				260
	6.40% Senior secured notes due 2017	425				425
	6.00% Senior secured notes due 2018(b)	179				179
	5.10% Senior secured notes due 2018	199				199
	6.70% Senior secured notes due 2019(b)	329				329
	5.10% Senior secured notes due 2019	244				244
	5.00% Senior secured notes due 2020	85				85
	5.50% Senior secured notes due 2034	184				184
	5.30% Senior secured notes due 2037	300				300
	8.45% Senior secured notes due 2039(b)	350				350
	3.90% Senior secured notes due 2042(b)	485				485
	Environmental improvement and pollution control revenue bonds:
	1992 Series due 2022(c)(d)	47				47
	1993 5.45% Series due 2028(e)	(e)				44
	1998 Series A due 2033(c)(d)	60				60
	1998 Series B due 2033(c)(d)	50				50
	1998 Series C due 2033(c)(d)	50				50
	Capital lease obligations:
	City of Bowling Green capital lease (Peno Creek CT) through 2022	59				64
	Audrain County capital lease (Audrain County CT) due 2023	240				240
	Total long-term debt, gross	3,764				4,013
	Less: Unamortized discount and premium	(7		)		(7		)
	Less: Maturities due within one year	(109		)		(205		)
	Long-term debt, net	$	3,648			$	3,801
		2013				2012
	Ameren Illinois:
	Senior secured notes:
	8.875% Senior secured notes due 2013(f)	$	—			$	150
	6.20% Senior secured notes due 2016(f)	54				54
	6.25% Senior secured notes due 2016(g)	75				75
	6.125% Senior secured notes due 2017(g)(h)	250				250
	6.25% Senior secured notes due 2018(g)(h)	144				144
	9.75% Senior secured notes due 2018(g)(h)	313				313
	2.70% Senior secured notes due 2022(g)(h)	400				400
	6.125% Senior secured notes due 2028(g)	60				60
	6.70% Senior secured notes due 2036(g)	61				61
	6.70% Senior secured notes due 2036(f)	42				42
	4.80% Senior secured notes due 2043(g)	280				—
	Environmental improvement and pollution control revenue bonds:
	5.90% Series 1993 due 2023(i)	32				32
	5.70% 1994A Series due 2024(j)	36				36
	1993 Series C-1 5.95% due 2026(k)	35				35
	1993 Series C-2 5.70% due 2026(k)	8				8
	1993 Series B-1 due 2028(d)(k)	17				17
	5.40% 1998A Series due 2028(j)	19				19
	5.40% 1998B Series due 2028(j)	33				33
	Fair-market value adjustments	4				4
	Total long-term debt, gross	1,863				1,733
	Less: Unamortized discount and premium	(7		)		(6		)
	Less: Maturities due within one year	—				(150		)
Long-term debt, net	$	1,856			$	1,577
Ameren consolidated long-term debt, net	$	5,504			$	5,802
(a)	These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.
(b)	Ameren Missouri has agreed, during the life of these notes, not to optionally redeem, purchase or otherwise retire in full its first mortgage bonds. Ameren Missouri has also agreed to prevent a first mortgage bond release date from occurring as long as any of the 8.45% senior secured notes due 2039 and any of the 3.90% senior secured notes due 2042 remain outstanding.
(c)	These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri's senior secured notes. The bonds are also backed by an insurance guarantee policy.
(d)	Interest rates, and periods during which such rates apply, vary depending on our selection of defined rate modes. Maximum interest rates could range up to 18% depending on the series of bonds. The average interest rates for 2013 and 2012 were as follows:
	2013		2012
Ameren Missouri 1992 Series	0.17%		0.30%
Ameren Missouri 1998 Series A	0.34%		0.65%
Ameren Missouri 1998 Series B	0.33%		0.64%
Ameren Missouri 1998 Series C	0.34%		0.64%
Ameren Illinois 1993 Series B-1	0.14%		0.22%
(e)	These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.
(f)	These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the CILCO mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the CILCO first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2023.
(g)	These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.
(h)	Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.
(i)	These bonds are first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture and are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value.
(j)	These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy.
(k)	The bonds are callable at 100% of par value.
The following table presents the aggregate maturities of long-term debt, including current maturities, for the Ameren Companies at December 31, 2013:
	Ameren				Ameren				Ameren				Ameren
	(Parent)(a)				Missouri(a)				Illinois(a)(b)				Consolidated
2014	$	425			$	109			$	—			$	534
2015	—				120				—				120
2016	—				266				129				395
2017	—				431				250				681
2018	—				383				457				840
Thereafter	—				2,455				1,023				3,478
Total	$	425			$	3,764			$	1,859			$	6,048
(a)	Excludes unamortized discount and premium of $7 million and $7 million at Ameren Missouri and Ameren Illinois, respectively.
(b)	Excludes $4 million related to Ameren Illinois’ long-term debt fair-market value adjustments, which are being amortized to interest expense over the remaining life of the debt.
All classes of Ameren Missouri’s and Ameren Illinois’ preferred stock are entitled to cumulative dividends and have voting rights. Preferred stock not subject to mandatory redemption of Ameren's subsidiaries was included in "Noncontrolling Interests" on Ameren's consolidated balance sheet. The following table presents the outstanding preferred stock of Ameren Missouri and Ameren Illinois that is not subject to mandatory redemption. The preferred stock is redeemable, at the option of the issuer, at the prices shown below as of December 31, 2013, and 2012:
			Redemption Price(per share)				2013				2012
Ameren Missouri:
Without par value and stated value of $100 per share, 25 million shares authorized
$3.50 Series	130,000 shares		$	110			$	13			$	13
$3.70 Series	40,000 shares		104.75				4				4
$4.00 Series	150,000 shares		105.625				15				15
$4.30 Series	40,000 shares		105				4				4
$4.50 Series	213,595 shares		110			(a)	21				21
$4.56 Series	200,000 shares		102.47				20				20
$4.75 Series	20,000 shares		102.176				2				2
$5.50 Series A	14,000 shares		110				1				1
Total							$	80			$	80
Ameren Illinois:
With par value of $100 per share, 2 million shares authorized
4.00% Series	144,275 shares		$	101			$	14			$	14
4.08% Series	45,224 shares		103				5				5
4.20% Series	23,655 shares		104				2				2
4.25% Series	50,000 shares		102				5				5
4.26% Series	16,621 shares		103				2				2
4.42% Series	16,190 shares		103				2				2
4.70% Series	18,429 shares		103				2				2
4.90% Series	73,825 shares		102				7				7
4.92% Series	49,289 shares		103.5				5				5
5.16% Series	50,000 shares		102				5				5
6.625% Series	124,274 shares		100				12				12
7.75% Series	4,542 shares		100				1				1
Total							$	62			$	62
Total Ameren							$	142			$	142
(a)	In the event of voluntary liquidation, $105.50.
Ameren has 100 million shares of $0.01 par value preferred stock authorized, with no shares outstanding. Ameren Missouri has 7.5 million shares of $1 par value preference stock authorized, with no such preference stock outstanding. Ameren Illinois has 2.6 million shares of no par value preferred stock authorized, with no shares outstanding.
Ameren
Ameren filed a Form S-8 registration statement with the SEC in October 2013, authorizing the offering of 4 million additional shares of its common stock under its 401(k) plan. Shares of common stock sold under the 401(k) plan are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated transactions.
Ameren filed a Form S-3 registration statement with the SEC in June 2011, authorizing the offering of 6 million additional shares of its common stock under DRPlus. Shares of common stock sold under DRPlus are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated transactions. In 2013 and 2012, Ameren shares were purchased in the open market for DRPlus and its 401(k) plan. Under DRPlus and its 401(k) plan, Ameren issued 2.2 million shares of common stock in 2011, which were valued at $65 million.
Ameren Missouri
In October 2013, $44 million of Ameren Missouri’s 1993 5.45% Series tax-exempt first mortgage bonds were redeemed at par value plus accrued interest, and $200 million of Ameren Missouri’s 4.65% senior secured notes matured and were retired.
On September 11, 2012, Ameren Missouri issued $485 million principal amount of 3.90% senior secured notes due September 15, 2042, with interest payable semiannually on March 15 and September 15 of each year, beginning March 15, 2013. These notes are secured by first mortgage bonds. Ameren Missouri received net proceeds of $478 million. The proceeds were used, together with other available cash, to provide the funds necessary to complete Ameren Missouri's tender offer on September 20, 2012, including the payment of interest and all related fees and expenses, and to retire the $173 million principal amount 5.25% senior secured notes that matured in September 2012.
On September 20, 2012, Ameren Missouri completed its tender offer to purchase for cash its outstanding 6.00% senior secured notes due 2018, 6.70% senior secured notes due 2019, 5.10% senior secured notes due 2018, and 5.10% senior secured notes due 2019. Any notes that were not tendered and purchased in the tender offer remain outstanding and continue to be obligations of Ameren Missouri. The following table sets forth the aggregate principal amount of each series of notes repurchased, along with certain other items related to the tender offer:
Senior Secured Notes	Principal Amount Repurchased				Premium Plus Accrued				Principal Amount Outstanding After Tender Offer
					and Unpaid Interest(a)
6.00% senior secured notes due 2018	$	71			$	19			$	179
6.70% senior secured notes due 2019	121				35				329
5.10% senior secured notes due 2018	1				(b)				199
5.10% senior secured notes due 2019	56				12				244
(a)	The premiums paid in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $485 million 3.90% senior secured notes due 2042.
(b)	Amount is less than $1 million.
Ameren Illinois
In January 2014, Ameren Illinois redeemed the following environmental improvement and pollution control revenue bonds at par value plus accrued interest:
Senior Secured Notes	Principal Amount
5.90% Series 1993 due 2023(a)	$	32
5.70% 1994A Series due 2024(a)	36
1993 Series C-1 5.95% due 2026	35
1993 Series C-2 5.70% due 2026	8
5.40% 1998A Series due 2028	19
5.40% 1998B Series due 2028	33
Total amount redeemed	$	163
(a)	Less than $1 million principal amount of the bonds remain outstanding as of January 31, 2014.
In December 2013, Ameren Illinois issued $280 million principal amount of 4.80% senior secured notes due December 15, 2043, with interest payable semiannually on June 15 and December 15 of each year, beginning June 15, 2014. These notes are secured by first mortgage bonds. Ameren Illinois received net proceeds of $276 million. The proceeds were used, together with other available cash, to repay at maturity $150 million aggregate principal amount of its 8.875% senior secured notes due December 15, 2013, and to repay its short-term debt.
On August 20, 2012, Ameren Illinois issued $400 million principal amount of 2.70% senior secured notes due September 1, 2022, with interest payable semiannually on March 1 and September 1 of each year, beginning March 1, 2013. These notes are secured by first mortgage bonds. Ameren Illinois received net proceeds of $397 million. The proceeds were used, together with other available cash, to provide the funds necessary to complete Ameren Illinois' tender offer on August 27, 2012, including the payment of interest and all related fees and expenses, and to redeem $51 million principal amount of 5.50% pollution control revenue bonds at par value plus accrued interest.
On August 27, 2012, Ameren Illinois completed its tender offer to purchase for cash its outstanding 9.75% senior secured notes due 2018 and 6.25% senior secured notes due 2018. Any notes that were not tendered and purchased in the tender offer remain outstanding and continue to be obligations of Ameren Illinois. The following table sets forth the aggregate principal amount of each series of notes repurchased, along with certain other items related to the tender offer:
Senior Secured Notes	Principal Amount Repurchased				Premium Plus Accrued				Principal Amount Outstanding After Tender Offer
					and Unpaid Interest(a)
9.75% senior secured notes due 2018	$	87			$	36			$	313
6.25% senior secured notes due 2018	194				47				144
(a)	Premiums paid in the amount of $21 million in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $400 million 2.70% senior secured notes due 2022. Premiums of $15 million were expensed in 2013 as a result of disallowances in the ICC's December 2013 electric and natural gas rate orders. See Note 2 – Rate and Regulatory Matters for further information regarding the disallowances.
In November 2012, $1 million principal amount of Ameren Illinois' 6.20% Series 1992B Pollution Control revenue bonds matured and were retired.
Indenture Provisions and Other Covenants
Ameren Missouri’s and Ameren Illinois’ indentures and articles of incorporation include covenants and provisions related to issuances of first mortgage bonds and preferred stock. Ameren Missouri and Ameren Illinois are required to meet certain ratios to issue additional first mortgage bonds and preferred stock. A failure to achieve these ratios would not result in a default under these covenants and provisions but would restrict the companies’ ability to issue bonds or preferred stock. The following table summarizes the required and actual interest coverage ratios for interest charges and dividend coverage ratios and bonds and preferred stock issuable as of December 31, 2013, at an assumed interest rate of 6% and dividend rate of 7%.
	Required Interest	Actual Interest		Bonds Issuable(b)				Required Dividend	Actual Dividend		Preferred Stock
	Coverage Ratio(a)	Coverage Ratio						Coverage Ratio(c)	Coverage Ratio		Issuable
Ameren Missouri	>2.0	4.5		$	3,831			>2.5	116.5		$	2,228
Ameren Illinois	>2.0	6.8		3,565			(d)	>1.5	2.4		203
(a)	Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.
(b)	Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $729 million and $365 million at Ameren Missouri and Ameren Illinois, respectively.
(c)	Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.
(d)	Amount of bonds issuable by Ameren Illinois based on unfunded property additions and retired bonds solely under the former IP mortgage indenture.
Ameren’s indenture does not require Ameren to comply with any quantitative financial covenants. The indenture does, however, include certain cross-default provisions. Specifically, either (1) the failure by Ameren to pay when due and upon expiration of any applicable grace period any portion of any Ameren indebtedness in excess of $25 million or (2) the acceleration upon default of the maturity of any Ameren indebtedness in excess of $25 million under any indebtedness agreement, including the 2012 Credit Agreements, constitutes a default under the indenture, unless such past due or accelerated debt is discharged or the acceleration is rescinded or annulled within a specified period.
Ameren Missouri and Ameren Illinois and certain other nonregistrant Ameren subsidiaries are subject to Section 305(a) of the Federal Power Act, which makes it unlawful for any officer or director of a public utility, as defined in the Federal Power Act, to participate in the making or paying of any dividend from any funds “properly included in capital account.” FERC has consistently interpreted the provision to allow dividends to be paid as long as (1) the source of the dividends is clearly disclosed, (2) the dividends are not excessive, and (3) there is no self-dealing on the part of corporate officials. At a minimum, Ameren believes that dividends can be paid by its subsidiaries that are public utilities from net income and retained earnings. In addition, under Illinois law, Ameren Illinois may not pay any dividend on its stock, unless, among other things, its earnings and earned surplus are sufficient to declare and pay a dividend after provision is made for reasonable and proper reserves, or unless Ameren Illinois has specific authorization from the ICC.
Ameren Illinois’ articles of incorporation require dividend payments on its common stock to be based on ratios of common stock to total capitalization and other provisions related to certain operating expenses and accumulations of earned surplus. Ameren Illinois committed to FERC to maintain a minimum 30% ratio of common stock equity to total capitalization. As of December 31, 2013, Ameren Illinois’ ratio of common stock equity to total capitalization was 55%.
In order for the Ameren Companies to issue securities in the future, they will have to comply with all applicable requirements in effect at the time of any such issuances.
Off-Balance-Sheet Arrangements
At December 31, 2013, none of the Ameren Companies had any off-balance-sheet financing arrangements, other than operating leases entered into in the ordinary course of business. None of the Ameren Companies expect to engage in any significant off-balance-sheet financing arrangements in the near future. See Note 16 – Divestiture Transactions and Discontinued Operations for Ameren (parent) guarantees and letters of credit issued to support New AER based on the transaction agreement with IPH.

Other_Income_And_Expenses

Other Income And Expenses	12 Months Ended
	Dec. 31, 2013
Other Nonoperating Income (Expense) [Abstract]	'
OTHER INCOME AND EXPENSES	'
	OTHER INCOME AND EXPENSES
	The following table presents the components of "Other Income and Expenses" in the Ameren Companies’ statements of income (loss) for the years ended December 31, 2013, 2012, and 2011:
		2013		2012			2011
	Ameren:(a)
	Miscellaneous income:
	Allowance for equity funds used during construction	$	37	$	36		$	34
	Interest income on industrial development revenue bonds	27		28			28
	Interest and dividend income	3		4		(b)	3
	Other	2		2			3
	Total miscellaneous income	$	69	$	70		$	68
	Miscellaneous expense:
	Donations	$	12	$	24	(c)	$	8
	Other	14		13			15
	Total miscellaneous expense	$	26	$	37		$	23
	Ameren Missouri:
	Miscellaneous income:
	Allowance for equity funds used during construction	$	31	$	31		$	30
	Interest income on industrial development revenue bonds	27		28			28
	Interest and dividend income	—		4		(b)	2
	Other	—		—			1
	Total miscellaneous income	$	58	$	63		$	61
	Miscellaneous expense:
	Donations	$	4	$	9		$	3
	Other	7		5			7
	Total miscellaneous expense	$	11	$	14		$	10
	Ameren Illinois:
	Miscellaneous income:
	Allowance for equity funds used during construction	$	6	$	5		$	4
	Interest and dividend income	2		—			1
	Other	2		2			2
	Total miscellaneous income	$	10	$	7		$	7
	Miscellaneous expense:
	Donations	$	4	$	11	(c)	$	1
	Other	5		6			5
	Total miscellaneous expense	$	9	$	17		$	6
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	Includes interest income received in 2012 relating to a refund of charges included in an expired power purchase agreement with Entergy. See Note 2 – Rate and Regulatory Matters for additional information.
	(c)	Includes Ameren Illinois' one-time $7.5 million donation to the Illinois Science and Energy Innovation Trust pursuant to the IEIMA as a result of Ameren Illinois' 2012 participation in the electric delivery formula ratemaking process.

Derivative_Financial_Instrumen

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2013
Derivative Instrument Detail [Abstract]	'
DERIVATIVE FINANCIAL INSTRUMENTS	'
	DERIVATIVE FINANCIAL INSTRUMENTS
	We use derivatives principally to manage the risk of changes in market prices for natural gas, diesel, power, and uranium. Such price fluctuations may cause the following:
	•	an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices;
	•	market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; and
	•	actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays.
	The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.
	The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2013, and 2012. As of December 31, 2013, these contracts ran through October 2016, October 2019, May 2032, and October 2016 for fuel oils, natural gas, power, and uranium, respectively.
		Quantity (in millions, except as indicated)
		2013			2012
	Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
	Fuel oils (in gallons)(a)	66	(b)	66	70	(b)	70
	Natural gas (in mmbtu)	28	108	136	19	128	147
	Power (in megawatthours)	3	11	14	11	14	25
	Uranium (pounds in thousands)	796	(b)	796	446	(b)	446
	(a)	Fuel oils consist of heating oil, ultra-low-sulfur diesel, and crude oil.
	(b)	Not applicable.
	Authoritative accounting guidance regarding derivative instruments requires that all contracts considered to be derivative instruments be recorded on the balance sheet at their fair values, unless the NPNS exception applies. See Note 8 – Fair Value Measurements for discussion of our methods of assessing the fair value of derivative instruments. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery.
	If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine if it qualifies for hedge accounting. We also consider whether gains or losses resulting from such derivatives qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or regulatory liabilities in the period in which the change occurs. Ameren Missouri and Ameren Illinois believe derivative gains and losses deferred as regulatory assets and regulatory liabilities are probable of recovery or refund through future rates charged to customers. Regulatory assets and regulatory liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of December 31, 2013, and 2012, all contracts that qualify for hedge accounting receive regulatory deferral.
	Authoritative accounting guidance permits companies to offset fair value amounts recognized for the right to reclaim cash collateral (a receivable) or the obligation to return cash collateral (a liability) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. The Ameren Companies did not elect to adopt this guidance for any eligible commodity contracts.
	The following table presents the carrying value and balance sheet location of all derivative instruments as of December 31, 2013, and 2012:
		Balance Sheet Location		Ameren			Ameren			Ameren
				Missouri			Illinois
	2013
	Derivative assets not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	Other current assets	$	6		$	—		$	6
		Other assets		3			—			3
	Natural gas	Other current assets		1			1			2
	Power	Other current assets		23			—			23
		Total assets	$	33		$	1		$	34
	Derivative liabilities not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	MTM derivative liabilities	$	(b)		$	—		$	2
		Other current liabilities		2			—			—
		Other deferred credits and liabilities		1			—			1
	Natural gas	MTM derivative liabilities		(b)			27			32
		Other current liabilities		5			—			—
		Other deferred credits and liabilities		6			19			25
	Power	MTM derivative liabilities		(b)			9			13
		Other current liabilities		4			—			—
		Other deferred credits and liabilities		—			99			99
	Uranium	MTM derivative liabilities		(b)			—			5
		Other current liabilities		5			—			—
		Other deferred credits and liabilities		1			—			1
		Total liabilities	$	24		$	154		$	178
	2012
	Derivative assets not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	Other current assets	$	8		$	—		$	8
		Other assets		4			—			4
	Natural gas	Other current assets		—			1			1
		Other assets		1			—			1
	Power	Other current assets		14			—			14
		Other assets		1			—			1
		Total assets	$	28		$	1		$	29
	Derivative liabilities not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	MTM derivative liabilities	$	(b)		$	—		$	2
		Other current liabilities		2			—			—
		Other deferred credits and liabilities		2			—			2
	Natural gas	MTM derivative liabilities		(b)			56			64
		Other current liabilities		8			—			—
		Other deferred credits and liabilities		7			38			45
Power	MTM derivative liabilities		(b)			21			25
	Other current liabilities		4			—			—
	Other deferred credits and liabilities		—			90			90
Uranium	MTM derivative liabilities		(b)			—			1
	Other current liabilities		1			—			—
	Other deferred credits and liabilities		1			—			1
	Total liabilities	$	25		$	205		$	230
(a)	Includes derivatives subject to regulatory deferral.
(b)	Balance sheet line item not applicable to registrant.
The following table presents the cumulative amount of pretax net gains (losses) on all derivative instruments deferred in regulatory assets or regulatory liabilities as of December 31, 2013, and 2012:
		Ameren			Ameren			Ameren
		Missouri			Illinois
2013
Cumulative gains (losses) deferred in regulatory liabilities or assets:
Fuel oils derivative contracts(a)	$	2		$	—		$	2
Natural gas derivative contracts(b)		(10	)		(45	)		(55	)
Power derivative contracts(c)		19			(108	)		(89	)
Uranium derivative contracts(d)		(6	)		—			(6	)
2012
Cumulative gains (losses) deferred in regulatory liabilities or assets:
Fuel oils derivative contracts(a)	$	4		$	—		$	4
Natural gas derivative contracts(b)		(14	)		(93	)		(107	)
Power derivative contracts(c)		12			(111	)		(99	)
Uranium derivative contracts(d)		(2	)		—			(2	)
(a)	Represents net gains on fuel oils derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri’s transportation costs for coal through October 2016, as of December 31, 2013. Current gains deferred as regulatory liabilities include $3 million and $3 million at Ameren and Ameren Missouri as of December 31, 2013, respectively. Current losses deferred as regulatory assets include $1 million and $1 million at Ameren and Ameren Missouri as of December 31, 2013, respectively.
(b)	Represents net losses associated with natural gas derivative contracts. These contracts are a partial hedge of natural gas requirements through October 2019 at Ameren and Ameren Missouri and through March 2017 at Ameren Illinois, in each case as of December 31, 2013. Current gains deferred as regulatory liabilities include $2 million, $1 million, and $1 million at Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2013. Current losses deferred as regulatory assets include $32 million, $5 million, and $27 million at Ameren, Ameren Missouri and Ameren Illinois, respectively, as of December 31, 2013.
(c)	Represents net gains (losses) associated with power derivative contracts. These contracts are a partial hedge of power price requirements through May 2032 at Ameren and Ameren Illinois and through December 2015 at Ameren Missouri, in each case as of December 31, 2013. Current gains deferred as regulatory liabilities include $23 million and $23 million at Ameren and Ameren Missouri, respectively, as of December 31, 2013. Current losses deferred as regulatory assets include $13 million, $4 million, and $9 million at Ameren, Ameren Missouri and Ameren Illinois, respectively, as of December 31, 2013.
(d)	Represents net losses on uranium derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri's uranium requirements through October 2016, as of December 31, 2013. Current losses deferred as regulatory assets include $5 million and $5 million at Ameren and Ameren Missouri as of December 31, 2013, respectively.
Derivative instruments are subject to various credit-related losses in the event of nonperformance by counterparties to the transaction. Exchange-traded contracts are supported by the financial and credit quality of the clearing members of the respective exchanges and have nominal credit risk. In all other transactions, we are exposed to credit risk. Our credit risk management program involves establishing credit limits and collateral requirements for counterparties, using master trading and netting agreements, and reporting daily exposure to senior management.
We believe that entering into master trading and netting agreements mitigates the level of financial loss that could result from default by allowing net settlement of derivative assets and liabilities. We generally enter into the following master trading and netting agreements: (1) the International Swaps and Derivatives Association Agreement, a standardized financial natural gas and electric contract; (2) the Master Power Purchase and Sale Agreement, created by the Edison Electric Institute and the National Energy Marketers Association, a standardized contract for the purchase and sale of wholesale power; and (3) the North American Energy Standards Board Inc. agreement, a standardized contract for the purchase and sale of natural gas. These master trading and netting agreements allow the counterparties to net settle sale and purchase transactions. Further, collateral requirements are calculated at the master trading and netting agreement level by counterparty.
Although Ameren had not previously elected to offset fair value amounts and collateral for derivative instruments executed with the same counterparty under the same master netting arrangement, authoritative accounting guidance, effective in the first quarter 2013, requires those amounts eligible to be offset to be presented both at the gross and net amounts. The following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of December 31, 2013, and 2012:
					Gross Amounts Not Offset in the Balance Sheet
		Gross Amounts Recognized in the Balance Sheet			Derivative Instruments			Cash Collateral Received/Posted(a)			Net
											Amount
2013
Commodity contracts eligible to be offset:
Assets:
Ameren Missouri	$	33		$	9		$	—		$	24
Ameren Illinois		1			1			—			—
Ameren	$	34		$	10		$	—		$	24
Liabilities:
Ameren Missouri	$	24		$	9		$	9		$	6
Ameren Illinois		154			1			15			138
Ameren	$	178		$	10		$	24		$	144
2012
Commodity contracts eligible to be offset:
Assets:
Ameren Missouri	$	28		$	9		$	—		$	19
Ameren Illinois		1			1			—			—
Ameren	$	29		$	10		$	—		$	19
Liabilities:
Ameren Missouri	$	25		$	9		$	7		$	9
Ameren Illinois		205			1			58			146
Ameren	$	230		$	10		$	65		$	155
(a)	Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” and “Other assets” on the balance sheet.
Concentrations of Credit Risk
In determining our concentrations of credit risk related to derivative instruments, we review our individual counterparties and categorize each counterparty into groupings according to the primary business in which each engages. We calculate maximum exposures based on the gross fair value of financial instruments, including accrual and NPNS contracts. As of December 31, 2013, if counterparty groups were to fail completely to perform on contracts, Ameren, Ameren Missouri, and Ameren Illinois' maximum exposure was $13 million, $12 million, and $1 million, respectively. As of December 31, 2012, if counterparty groups were to fail completely to perform on contracts, Ameren, Ameren Missouri, and Ameren Illinois' maximum exposure was $23 million, $22 million, and $1 million, respectively. The potential loss on counterparty exposures is reduced by the application of master trading and netting agreements and collateral held to the extent of reducing the exposure to zero. As of December 31, 2013, the potential loss after consideration of the application of master trading and netting agreements and collateral held for Ameren and Ameren Missouri was $6 million and $6 million, respectively. As of December 31, 2012, the potential loss after consideration of the application of master trading and netting agreements and collateral held for Ameren and Ameren Missouri was $15 million and $15 million, respectively.
Derivative Instruments with Credit Risk-Related Contingent Features
Our commodity contracts contain collateral provisions tied to the Ameren Companies’ credit ratings. If we were to experience an adverse change in our credit ratings, or if a counterparty with reasonable grounds for uncertainty regarding performance of an obligation requested adequate assurance of performance, additional collateral postings might be required. The following table presents, as of December 31, 2013, and 2012, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that could be required to be posted with counterparties. The additional collateral required is the net liability position allowed under the master trading and netting agreements assuming (1) the credit risk-related contingent features underlying these agreements were triggered on December 31, 2013, or 2012, respectively, and (2) those counterparties with rights to do so requested collateral:
	Aggregate Fair Value of				Cash				Potential Aggregate Amount of
	Derivative Liabilities(a)				Collateral Posted				Additional Collateral Required(b)
2013
Ameren Missouri	$	70			$	2			$	67
Ameren Illinois	75				15				55
Ameren	$	145			$	17			$	122
2012
Ameren Missouri	$	78			$	3			$	71
Ameren Illinois	148				58				84
Ameren	$	226			$	61			$	155
(a)	Prior to consideration of master trading and netting agreements and including NPNS and accrual contract exposures.
(b)	As collateral requirements with certain counterparties are based on master trading and netting agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such agreements.
Derivatives Subject to Regulatory Deferral
The following table represents the net change in market value associated with derivatives that qualify for regulatory deferral for the years ended December 31, 2013 and 2012:
			Gain (Loss) Recognized
			in Regulatory Liabilities
			or Regulatory Assets
			2013				2012
Ameren (a)	Fuel oils		$	(2	)		$	(15	)
	Natural gas		52				84
	Power		10				(180		)
	Uranium		(4		)		(1		)
	Total		$	56			$	(112	)
Ameren Missouri	Fuel oils		$	(2	)		$	(15	)
	Natural gas		4				10
	Power		7				(9		)
	Uranium		(4		)		(1		)
	Total		$	5			$	(15	)
Ameren Illinois	Natural gas		$	48			$	74
	Power		3				29
	Total		$	51			$	103
(a)	Amounts include intercompany eliminations.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
FAIR VALUE MEASUREMENTS	'
	FAIR VALUE MEASUREMENTS
	Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. We use various methods to determine fair value, including market, income, and cost approaches. With these approaches, we adopt certain assumptions that market participants would use in pricing the asset or liability, including assumptions about market risk or the risks inherent in the inputs to the valuation. Inputs to valuation can be readily observable, market-corroborated, or unobservable. We use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. Authoritative accounting guidance established a fair value hierarchy that prioritizes the inputs used to measure fair value. All financial assets and liabilities carried at fair value are classified and disclosed in one of the following three hierarchy levels:
	Level 1: Inputs based on quoted prices in active markets for identical assets or liabilities. Level 1 assets and liabilities are primarily exchange-traded derivatives and assets, including cash and cash equivalents and listed equity securities, such as those held in Ameren Missouri’s nuclear decommissioning trust fund.
	The market approach is used to measure the fair value of equity securities held in Ameren Missouri's nuclear decommissioning trust fund. Equity securities in this fund are representative of the S&P 500 index, excluding securities of Ameren Corporation, owners and/or operators of nuclear power plants and the trustee and investment managers. The S&P 500 index comprises stocks of large capitalization companies.
	Level 2: Market-based inputs corroborated by third-party brokers or exchanges based on transacted market data. Level 2 assets and liabilities include certain assets held in Ameren Missouri’s nuclear decommissioning trust fund, including corporate bonds and other fixed-income securities, United States treasury and agency securities, and certain over-the-counter derivative instruments, including natural gas and financial power transactions.
	Fixed income securities are valued using prices from independent industry recognized data vendors who provide values that are either exchange-based or matrix-based. The fair value measurements of fixed income securities classified as Level 2 are based on inputs other than quoted prices that are observable for the asset or liability. Examples are matrix pricing, market corroborated pricing, and inputs such as yield curves and indices. Level 2 fixed income securities in the nuclear decommissioning trust fund are primarily corporate bonds, asset-backed securities and United States agency bonds.
	Derivative instruments classified as Level 2 are valued by corroborated observable inputs, such as pricing services or prices from similar instruments that trade in liquid markets. Our development and corroboration process entails obtaining multiple quotes or prices from outside sources. To derive our forward view to price our derivative instruments at fair value, we average the midpoints of the bid/ask spreads. To validate forward prices obtained from outside parties, we compare the pricing to recently settled market transactions. Additionally, a review of all sources is performed to identify any anomalies or potential errors. Further, we consider the volume of transactions on certain trading platforms in our reasonableness assessment of the averaged midpoint. Natural gas derivative contracts are valued based upon exchange closing prices without significant unobservable adjustments. Power derivatives contracts are valued based upon the use of multiple forward prices provided by third parties. The prices are averaged and shaped to a monthly profile when needed without significant unobservable adjustments.
	Level 3: Unobservable inputs that are not corroborated by market data. Level 3 assets and liabilities are valued by internally developed models and assumptions or methodologies that use significant unobservable inputs. Level 3 assets and liabilities include derivative instruments that trade in less liquid markets, where pricing is largely unobservable. We value Level 3 instruments by using pricing models with inputs that are often unobservable in the market, as well as certain internal assumptions. Our development and corroboration process entails obtaining multiple quotes or prices from outside sources. As a part of our reasonableness review, an evaluation of all sources is performed to identify any anomalies or potential errors.
	We perform an analysis each quarter to determine the appropriate hierarchy level of the assets and liabilities subject to fair value measurements. Financial assets and liabilities are classified in their entirety according to the lowest level of input that is significant to the fair value measurement. All assets and liabilities whose fair value measurement is based on significant unobservable inputs are classified as Level 3.
	The following table describes the valuation techniques and unobservable inputs for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy for the period ended December 31, 2013:
			Fair Value									Weighted
			Assets			Liabilities			Valuation Technique(s)	Unobservable Input	Range	Average
	Level 3 Derivative asset and liability – commodity contracts(a):
	Ameren	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	Oct-35	16
									Discounted cash flow	Counterparty credit risk(%)(c)(d)	0.26 - 2	1
		Power(e)	21			(110		)	Discounted cash flow	Average forward peak and off-peak pricing - forwards/swaps($/MWh)(c)	25 - 51	32
										Estimated auction price for FTRs($/MW)(b)	(1,594) - 945	305
										Nodal basis($/MWh)(c)	(3) - (1)	-2
										Counterparty credit risk(%)(c)(d)	0.39 - 0.50	0.42
										Ameren credit risk(%)(c)(d)	2	(f)
									Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	5-Apr	5
										Escalation rate(%)(b)(g)	4-Mar	4
									Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
		Uranium	—			(6		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	34 - 41	36
	Ameren Missouri	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	Oct-35	16
									Discounted cash flow	Counterparty credit risk(%)(c)(d)	0.26 - 2	1
		Power(e)	21			(2		)	Discounted cash flow	Average forward peak and off-peak pricing - forwards/swaps($/MWh)(c)	25 - 51	40
										Estimated auction price for FTRs($/MW)(b)	(1,594) - 945	305
										Nodal basis($/MWh)(c)	(3) - (1)	-2
										Counterparty credit risk(%)(c)(d)	0.39 - 0.50	0.42
										Ameren Missouri credit risk(%)(c)(d)	2	(f)
		Uranium	—			(6		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	34 - 41	36
	Ameren Illinois	Power(e)	$	—		$	(108	)	Discounted cash flow	Average forward peak and off-peak pricing - forwards/swaps($/MWh)(b)	27 - 36	30
										Nodal basis($/MWh)(b)	(4) - 0	-2
										Ameren Illinois credit risk(%)(c)(d)	2	(f)
									Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	5-Apr	5
										Escalation rate(%)(b)(g)	4-Mar	4
									Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
	(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
	(b)	Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
	(c)	Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
	(d)	Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren, Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
	(e)	Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2017. Valuations beyond 2017 use fundamentally modeled pricing by month for peak and off-peak demand.
	(f)	Not applicable.
	(g)	Escalation rate applies to power prices 2026 and beyond.
	The following table describes the valuation techniques and unobservable inputs for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2012:
			Fair Value									Weighted
			Assets			Liabilities			Valuation Technique	Unobservable Input	Range	Average
	Level 3 Derivative asset and liability – commodity contracts(a):
	Ameren	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	27-Jul	24
									Discounted cash flow	Escalation rate(%)(b)	0.21 - 0.60	0.44
										Counterparty credit risk(%)(c)(d)	0.12 - 1	1
										Ameren credit risk(%)(c)(d)	2	(e)
		Power(f)	14			(114		)	Discounted cash flow	Average forward peak and off-peak power pricing - forwards/swaps($/MWh)(c)	22 - 47	31
										Estimated auction price for FTRs($/MW)(b)	(281) - 1,851	178
										Nodal basis($/MWh)(c)	(5) - (1)	-3
										Counterparty credit risk(%)(c)(d)	0.22 - 1	1
										Ameren credit risk(%)(c)(d)	5-Feb	5
									Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	8-Apr	6
									Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
		Uranium	—			(2		)	Discounted cash flow	Average forward uranium pricing($/pound)(b)	43 - 46	44
	Ameren Missouri	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	27-Jul	24
									Discounted cash flow	Escalation rate(%)(b)	0.21 - 0.60	0.44
									Counterparty credit risk(%)(c)(d)	0.12 - 1	1
									Ameren Missouri credit risk(%)(c)(d)	2	(e)
	Power(f)	14			(3		)	Discounted cash flow	Average forward peak and off-peak power pricing - forwards/swaps($/MWh)(c)	24 - 56	36
									Estimated auction price for FTRs($/MW)(b)	(281) - 1,851	178
									Nodal basis($/MWh)(c)	(5) - (1)	-2
									Counterparty credit risk(%)(c)(d)	0.22 - 1	1
									Ameren Missouri credit risk(%)(c)(d)	2	(e)
	Uranium	—			(2		)	Discounted cash flow	Average forward uranium pricing($/pound)(b)	43 - 46	44
Ameren Illinois	Power(f)	$	—		$	(111	)	Discounted cash flow	Average forward peak and off-peak power pricing - forwards/swaps($/MWh)(b)	22 - 47	30
									Nodal basis($/MWh)(b)	(5) - (1)	-3
									Ameren Illinois credit risk(%)(c)(d)	5	(e)
								Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	8-Apr	6
								Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)	Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
(c)	Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
(d)	Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren, Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
(e)	Not applicable.
(f)	Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2017. Valuations beyond 2017 use fundamentally modeled pricing by month for peak and off-peak demand.
In accordance with applicable authoritative accounting guidance, we consider nonperformance risk in our valuation of derivative instruments by analyzing the credit standing of our counterparties and considering any counterparty credit enhancements (e.g., collateral). The guidance also requires that the fair value measurement of liabilities reflect the nonperformance risk of the reporting entity, as applicable. Therefore, we have factored the impact of our credit standing, as well as any potential credit enhancements, into the fair value measurement of both derivative assets and derivative liabilities. Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. Ameren recorded no gains or losses related to valuation adjustments for counterparty default risk in 2013, 2012 or 2011. At December 31, 2013, the counterparty default risk liability valuation adjustment related to derivative contracts totaled $3 million, less than $1 million, and $3 million, for Ameren, Ameren Missouri, and Ameren Illinois, respectively. At December 31, 2012, the counterparty default risk liability valuation adjustment related to derivative contracts totaled $7 million, less than $1 million, and $7 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively.
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2013:
			Quoted Prices in				Significant Other				Significant Other				Total
			Active Markets for				Observable				Unobservable
			Identical Assets				Inputs				Inputs
			or Liabilities				(Level 2)				(Level 3)
			(Level 1)
Assets:
Ameren	Derivative assets – commodity contracts(a):
	Fuel oils		$	1			$	—			$	8			$	9
	Natural gas		—				2				—				2
	Power		—				2				21				23
	Total derivative assets – commodity contracts		$	1			$	4			$	29			$	34
	Nuclear decommissioning trust fund:
	Cash and cash equivalents		$	3			$	—			$	—			$	3
	Equity securities:
	U.S. large capitalization		332				—				—				332
	Debt securities:
	Corporate bonds		—				52				—				52
	Municipal bonds		—				2				—				2
	U.S. treasury and agency securities		—				94				—				94
	Asset-backed securities		—				10				—				10
	Other		—				1				—				1
	Total nuclear decommissioning trust fund		$	335			$	159			$	—			$	494
	Total Ameren		$	336			$	163			$	29			$	528
Ameren Missouri	Derivative assets – commodity contracts(a):
	Fuel oils		$	1			$	—			$	8			$	9
	Natural gas		—				1				—				1
	Power		—				2				21				23
	Total derivative assets – commodity contracts		$	1			$	3			$	29			$	33
	Nuclear decommissioning trust fund:
	Cash and cash equivalents		$	3			$	—			$	—			$	3
	Equity securities:
	U.S. large capitalization		332				—				—				332
	Debt securities:
	Corporate bonds		—				52				—				52
	Municipal bonds		—				2				—				2
	U.S. treasury and agency securities		—				94				—				94
	Asset-backed securities		—				10				—				10
	Other		—				1				—				1
	Total nuclear decommissioning trust fund		$	335			$	159			$	—			$	494
	Total Ameren Missouri		$	336			$	162			$	29			$	527
Ameren Illinois	Derivative assets – commodity contracts(a):
	Natural gas		$	—			$	1			$	—			$	1
Liabilities:
Ameren	Derivative liabilities – commodity contracts(a):
	Fuel oils		$	—			$	—			$	3			$	3
	Natural gas		3				54				—				57
	Power		—				2				110				112
	Uranium		—				—				6				6
	Total Ameren		$	3			$	56			$	119			$	178
Ameren Missouri	Derivative liabilities – commodity contracts(a):
	Fuel oils		$	—			$	—			$	3			$	3
	Natural gas		3				8				—				11
	Power		—				2				2				4
	Uranium		—				—				6				6
	Total Ameren Missouri		$	3			$	10			$	11			$	24
Ameren Illinois	Derivative liabilities – commodity contracts(a):
	Natural gas		$	—			$	46			$	—			$	46
	Power		—				—				108				108
	Total Ameren Illinois		$	—			$	46			$	108			$	154
(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2012:
			Quoted Prices in				Significant Other				Significant				Total
			Active Markets for				Observable Inputs				Other
			Identical Assets				(Level 2)				Unobservable
			or Liabilities								Inputs
			(Level 1)								(Level 3)
Assets:
Ameren	Derivative assets – commodity contracts(a):
	Fuel oils		$	4			$	—			$	8			$	12
	Natural gas		—				2				—				2
	Power		—				1				14				15
	Total derivative assets – commodity contracts		$	4			$	3			$	22			$	29
	Nuclear decommissioning trust fund:
	Cash and cash equivalents		$	1			$	—			$	—			$	1
	Equity securities:
	U.S. large capitalization		264				—				—				264
	Debt securities:
	Corporate bonds		—				47				—				47
	Municipal bonds		—				1				—				1
	U.S. treasury and agency securities		—				81				—				81
	Asset-backed securities		—				11				—				11
	Other		—				1				—				1
	Total nuclear decommissioning trust fund		$	265			$	141			$	—			$	406	(b)
	Total Ameren		$	269			$	144			$	22			$	435
Ameren Missouri	Derivative assets – commodity contracts(a):
	Fuel oils		$	4			$	—			$	8			$	12
	Natural gas		—				1				—				1
	Power		—				1				14				15
	Total derivative assets – commodity contracts		$	4			$	2			$	22			$	28
	Nuclear decommissioning trust fund:
	Cash and cash equivalents		$	1			$	—			$	—			$	1
	Equity securities:
	U.S. large capitalization		264				—				—				264
	Debt securities:
	Corporate bonds		—				47				—				47
	Municipal bonds		—				1				—				1
	U.S. treasury and agency securities		—				81				—				81
	Asset-backed securities		—				11				—				11
	Other		—				1				—				1
	Total nuclear decommissioning trust fund		$	265			$	141			$	—			$	406	(b)
	Total Ameren Missouri		$	269			$	143			$	22			$	434
Ameren Illinois	Derivative assets – commodity contracts(a):
	Natural gas		$	—			$	1			$	—			$	1
Liabilities:
Ameren	Derivative liabilities – commodity contracts(a):
	Fuel oils		$	1			$	—			$	3			$	4
	Natural gas		7				102				—				109
	Power		—				1				114				115
	Uranium		—				—				2				2
	Total Ameren		$	8			$	103			$	119			$	230
Ameren Missouri	Derivative liabilities – commodity contracts(a):
	Fuel oils		$	1			$	—			$	3			$	4
	Natural gas		7				8				—				15
	Power		—				1				3				4
	Uranium		—				—				2				2
	Total Ameren Missouri		$	8			$	9			$	8			$	25
Ameren Illinois	Derivative liabilities – commodity contracts(a):
	Natural gas		$	—			$	94			$	—			$	94
	Power		—				—				111				111
	Total Ameren Illinois		$	—			$	94			$	111			$	205
(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)	Balance excludes $2 million of receivables, payables, and accrued income, net.
The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2013:
		Net Derivative Commodity Contracts
		Ameren			Ameren			Ameren
		Missouri			Illinois
Fuel oils:
Beginning balance at January 1, 2013	$	5		$	(a)		$	5
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		—			(a)			—
Total realized and unrealized gains (losses)		—			(a)			—
Purchases		3			(a)			3
Sales		(1	)		(a)			(1	)
Settlements		(2	)		(a)			(2	)
Ending balance at December 31, 2013	$	5		$	(a)		$	5
Change in unrealized gains (losses) related to assets/liabilities held at December 31,2013	$	—		$	(a)		$	—
Natural gas:
Beginning balance at January 1, 2013	$	—		$	—		$	—
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		—			(1	)		(1	)
Total realized and unrealized gains (losses)		—			(1	)		(1	)
Purchases		—			1			1
Ending balance at December 31, 2013	$	—		$	—		$	—
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2013	$	—		$	—		$	—
Power:
Beginning balance at January 1, 2013	$	11		$	(111	)	$	(100	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		3			(18	)		(15	)
Total realized and unrealized gains (losses)		3			(18	)		(15	)
Purchases		40			—			40
Settlements		(36	)		21			(15	)
Transfers into Level 3		(3	)		—			(3	)
Transfers out of Level 3		4			—			4
Ending balance at December 31, 2013	$	19		$	(108	)	$	(89	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2013	$	(1	)	$	(24	)	$	(25	)
Uranium:
Beginning balance at January 1, 2013	$	(2	)	$	(a)		$	(2	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(3	)		(a)			(3	)
Total realized and unrealized gains (losses)		(3	)		(a)			(3	)
Purchases		(2	)		(a)			(2	)
Settlements		1			(a)			1
Ending balance at December 31, 2013	$	(6	)	$	(a)		$	(6	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2013	$	(2	)	$	(a)		$	(2	)
(a)	Not applicable.
The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2012:
		Net Derivative Commodity Contracts
		Ameren			Ameren			Ameren
		Missouri			Illinois
Fuel oils:
Beginning balance at January 1, 2012	$	3		$	(a)		$	3
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(1	)		(a)			(1	)
Total realized and unrealized gains (losses)		(1	)		(a)			(1	)
Purchases		7			(a)			7
Sales		(3	)		(a)			(3	)
Settlements		(2	)		(a)			(2	)
Transfers into Level 3		1			(a)			1
Ending balance at December 31, 2012	$	5		$	(a)		$	5
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	(1	)	$	(a)		$	(1	)
Natural gas:
Beginning balance at January 1, 2012	$	(14	)	$	(160	)	$	(174	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(2	)		(25	)		(27	)
Total realized and unrealized gains (losses)		(2	)		(25	)		(27	)
Settlements		1			15			16
Transfers out of Level 3		15			170			185
Ending balance at December 31, 2012	$	—		$	—		$	—
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	—		$	—		$	—
Power(b):
Beginning balance at January 1, 2012	$	21		$	(140	)	$	81
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		11			(226	)		(175	)
Total realized and unrealized gains (losses)		11			(226	)		(175	)
Purchases		21			—			21
Sales		(1	)		—			(1	)
Settlements		(37	)		255			(22	)
Transfers out of Level 3		(4	)		—			(4	)
Ending balance at December 31, 2012	$	11		$	(111	)	$	(100	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	—		$	(191	)	(c) $	(175	)
Uranium:
Beginning balance at January 1, 2012	$	(1	)	$	(a)		$	(1	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(2	)		(a)			(2	)
Total realized and unrealized gains (losses)		(2	)		(a)			(2	)
Settlements		1			(a)			1
Ending balance at December 31, 2012	$	(2	)	$	(a)		$	(2	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	(1	)	$	(a)		$	(1	)
(a)	Not applicable.
(b)	Ameren amounts include intercompany eliminations.
(c)	The change in unrealized losses was due to decreases in long-term power prices applied to 20-year Ameren Illinois swap contracts, which expire in May 2032.
Transfers in or out of Level 3 represent either (1) existing assets and liabilities that were previously categorized as a higher level but were recategorized to Level 3 because the inputs to the model became unobservable during the period, or (2) existing assets and liabilities that were previously classified as Level 3 but were recategorized to a higher level because the lowest significant input became observable during the period. Transfers out of Level 3 into Level 2 for natural gas derivatives were due to management previously using broker quotations to estimate the fair value of natural gas contracts and changing to estimates based upon exchange closing prices without significant unobservable adjustments in 2012. Estimates of fair value based on exchange closing prices are deemed to be a more accurate approximation of natural gas prices. Transfers between Level 2 and Level 3 for power derivatives and between Level 1 and Level 3 for fuel oils were primarily caused by changes in availability of financial trades observable on electronic exchanges between the periods shown below. Any reclassifications are reported as transfers out of Level 3 at the fair value measurement reported at the beginning of the period in which the changes occur. For the years ended December 31, 2013 and 2012, there were no transfers between Level 1 and Level 2 related to derivative commodity contracts. The following table summarizes all transfers between fair value hierarchy levels related to derivative commodity contracts for the years ended December 31, 2013 and 2012:
	2013				2012
Ameren - derivative commodity contracts:
Transfers into Level 3 / Transfers out of Level 1 – Fuel oils	$	—			$	1
Transfers out of Level 3 / Transfers into Level 2 – Natural gas	—				185
Transfers into Level 3 / Transfers out of Level 2 – Power	(3		)		—
Transfers out of Level 3 / Transfers into Level 2 – Power	4				(4		)
Net fair value of Level 3 transfers	$	1			$	182
Ameren Missouri - derivative commodity contracts:
Transfers into Level 3 / Transfers out of Level 1 – Fuel oils	$	—			$	1
Transfers out of Level 3 / Transfers into Level 2 – Natural gas	—				15
Transfers into Level 3 / Transfers out of Level 2 – Power	(3		)		—
Transfers out of Level 3 / Transfers into Level 2 – Power	4				(4		)
Net fair value of Level 3 transfers	$	1			$	12
Ameren Illinois - derivative commodity contracts:
Transfers out of Level 3 / Transfers into Level 2 – Natural gas	$	—			$	170
See Note 11 – Retirement Benefits for the fair value hierarchy tables detailing Ameren’s pension and postretirement plan assets as of December 31, 2013, as well as a table summarizing the changes in Level 3 plan assets during 2013.
The Ameren Companies’ carrying amounts of cash and cash equivalents approximate fair value because of the short-term nature of these instruments and are considered to be Level 1 in the fair value hierarchy. Ameren's and Ameren Missouri's carrying amounts of investments in debt securities related to the two CTs from the city of Bowling Green and Audrain County approximate fair value. These investments are classified as held-to-maturity. These investments are considered Level 2 in the fair value hierarchy as they are valued based on similar market transactions. The Ameren Companies' short-term borrowings also approximate fair value because of their short-term nature. Short-term borrowings are considered to be Level 2 in the fair value hierarchy as they are valued based on market rates for similar market transactions. The estimated fair value of long-term debt and preferred stock is based on the quoted market prices for same or similar issuances for companies with similar credit profiles or on the current rates offered to the Ameren Companies for similar financial instruments, which fair value measurement is considered Level 2 in the fair value hierarchy.
The following table presents the carrying amounts and estimated fair values of our long-term debt and preferred stock at December 31, 2013 and 2012:
	2013								2012
	Carrying Amount				Fair Value				Carrying Amount				Fair Value
Ameren:(a)
Long-term debt and capital lease obligations (including current portion)	$	6,038			$	6,584			$	6,157			$	7,110
Preferred stock	142				118				142				123
Ameren Missouri:
Long-term debt and capital lease obligations (including current portion)	$	3,757			$	4,124			$	4,006			$	4,625
Preferred stock	80				71				80				74
Ameren Illinois:
Long-term debt (including current portion)	$	1,856			$	2,028			$	1,727			$	2,020
Preferred stock	62				47				62				49
(a)	Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.

Nuclear_Decommissioning_Trust_

Nuclear Decommissioning Trust Fund Investments	12 Months Ended
	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'
NUCLEAR DECOMMISSIONING TRUST FUND INVESTMENTS	'
	NUCLEAR DECOMMISSIONING TRUST FUND INVESTMENTS
	Ameren Missouri has investments in debt and equity securities that are held in a trust fund for the purpose of funding the decommissioning of its Callaway energy center. We have classified these investments as available for sale, and we have recorded all such investments at their fair market value at December 31, 2013, and 2012. See Note 10 – Callaway Energy Center for additional information.
	Investments in the nuclear decommissioning trust fund have a target allocation of 60% to 70% in equity securities, with the balance invested in debt securities.
	The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2013, 2012, and 2011:
		2013		2012			2011
	Proceeds from sales and maturities	$	196	$	384		$	199
	Gross realized gains	7		6			5
	Gross realized losses	5		2			4
	Net realized and unrealized gains and losses are deferred and recorded as regulatory assets or regulatory liabilities on Ameren’s and Ameren Missouri’s balance sheets. This reporting is consistent with the method used to account for the decommissioning costs recovered in rates. Gains or losses associated with assets in the trust fund could result in lower or higher funding requirements for decommissioning costs, which are expected to be reflected in electric rates paid by Ameren Missouri’s customers. See Note 2 – Rate and Regulatory Matters.
	The following table presents the costs and fair values of investments in debt and equity securities in Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2013, and 2012:
	Security Type	Cost		Gross Unrealized Gain			Gross Unrealized Loss		Fair Value
	2013
	Debt securities	$	157	$	4	$	2		$	159
	Equity securities	137		199			4		332
	Cash	3		—			—		3
	Other(b)	(a)		—			—		(a)
	Total	$	297	$	203	$	6		$	494
	2012
	Debt securities	$	133	$	8	$	(a)		$	141
	Equity securities	145		130			11		264
	Cash	1		—			—		1
	Other(b)	2		—			—		2
	Total	$	281	$	138	$	11		$	408
	(a)	Amount less than $1 million.
	(b)	Represents payables relating to pending security purchases, net of receivables related to pending security sales and interest receivables.
	The following table presents the costs and fair values of investments in debt securities in Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2013:
		Cost		Fair Value
	Less than 5 years	$	93	$	94
	5 years to 10 years	31		32
	Due after 10 years	33		33
	Total	$	157	$	159
	We have unrealized losses relating to certain available-for-sale investments included in our decommissioning trust fund, recorded as regulatory assets as discussed above. Decommissioning will not occur until the operating license for our nuclear energy center expires. Ameren Missouri submitted a license extension application to the NRC to extend the Callaway energy center’s operating license to 2044. The following table presents the fair value and the gross unrealized losses of the available-for-sale securities held in Ameren Missouri's nuclear decommissioning trust fund. They are aggregated by investment category and the length of time that individual securities have been in a continuous unrealized loss position at December 31, 2013:
		Less than 12 Months						12 Months or Greater			Total
		Fair Value		Gross				Fair Value		Gross	Fair Value		Gross
				Unrealized						Unrealized			Unrealized
				Losses						Losses			Losses
	Debt securities	$	72	$	2		$	(a)	$	(a)	$	72	$	2
	Equity securities	6		(a)				7		4	13		4
	Total	$	78	$	2		$	7	$	4	$	85	$	6
	(a)	Amount less than $1 million.

Callaway_Energy_Center

Callaway Energy Center	12 Months Ended
	Dec. 31, 2013
Nuclear Waste Matters [Abstract]	'
CALLAWAY ENERGY CENTER	'
	CALLAWAY ENERGY CENTER
	Under the NWPA, the DOE is responsible for disposing of spent nuclear fuel from the Callaway energy center and other commercial nuclear energy centers. Under the NWPA, Ameren and other utilities that own and operate those energy centers are responsible for paying the disposal costs. The NWPA established the fee that these utilities pay the federal government for disposing of the spent nuclear fuel at one mill, or one-tenth of one cent, for each kilowatthour generated by those plants and sold. The NWPA also requires the DOE to review the nuclear waste fee against the cost of the nuclear waste disposal program and to propose to the United States Congress any fee adjustment necessary to offset the costs of the program. As required by the NWPA, Ameren Missouri and other utilities have entered into standard contracts with the federal government. The government, represented by the DOE, is responsible for implementing these provisions of the NWPA. Consistent with the NWPA and its standard contract, Ameren Missouri collects one mill from its electric customers for each kilowatthour of electricity that it generates and sells from its Callaway energy center.
	Although both the NWPA and the standard contract stated that the federal government would begin to dispose of spent nuclear fuel by 1998, the federal government is not meeting its disposal obligation. Ameren Missouri has sufficient installed capacity at the Callaway energy center to store its spent nuclear fuel generated through 2020, and it has the capability for additional storage capacity for spent nuclear fuel generated through the end of the energy center’s current licensed life. The DOE's delay in carrying out its obligation to dispose of spent nuclear fuel from the Callaway energy center is not expected to adversely affect the continued operations of the energy center.
	In January 2009, the federal government announced that a spent nuclear fuel repository at Yucca Mountain, Nevada was unworkable. The federal government took steps to terminate the Yucca Mountain program, while acknowledging its continuing obligation to dispose of utilities’ spent nuclear fuel. In January 2013, the DOE issued its plan for the management and disposal of spent nuclear fuel. The DOE's plan calls for a pilot interim storage facility to begin operation with an initial focus on accepting spent nuclear fuel from shutdown reactor sites by 2021. By 2025, a larger interim storage facility would be available, co-located with the pilot facility. The plan also proposes to site a permanent geological repository by 2026, to characterize the site and to design and to license the repository by 2042, and to begin operation by 2048.
	In view of the federal government's efforts to terminate the Yucca Mountain program, the Nuclear Energy Institute, a number of individual utilities, and the National Association of Regulatory Utility Commissioners sued the DOE in the United States Court of Appeals for the District of Columbia Circuit, seeking the suspension of the one mill nuclear waste fee, alleging that the DOE failed to undertake an appropriate fee adequacy review reflecting the current unsettled state of the nuclear waste program. In a June 2012 decision, the court ruled that DOE's fee adequacy review was legally inadequate and remanded the matter to the DOE. Although the court ruled it has the power to direct the DOE to suspend the fee, the court decided that it was premature to do so. Instead, the court ordered the DOE to provide within six months a revised assessment of the amount that should be collected. In January 2013, the DOE issued the revised assessment required by the court. The DOE determined that “neither insufficient nor excess revenues are being collected,” and it proposed no adjustment to the one mill nuclear waste fee. In November 2013, the court rejected the DOE's revised assessment and ordered the DOE to submit a proposal to the United States Congress to reduce the fee to zero. The DOE filed for rehearing, however there is no deadline for the court to act. In January 2014, the DOE, pursuant to the court's November 2013 order, submitted to Congress a proposal to reduce the fee to zero.
	As a result of the DOE's failure to begin to dispose of the utilities' spent nuclear fuel and fulfill its contractual obligations, Ameren Missouri and other nuclear energy center owners have also sued the DOE to recover costs incurred for ongoing storage of their spent fuel. Ameren Missouri filed a breach of contract lawsuit to recover costs that it incurred through 2009. It sought reimbursement for the cost of reracking the Callaway energy center’s spent fuel pool, as well as certain NRC fees, and Missouri ad valorem taxes that Ameren Missouri would not have incurred had the DOE performed its contractual obligations. In June 2011, the parties reached a settlement agreement that included a payment to Ameren Missouri of $11 million for spent fuel storage and related costs through 2010. In addition, the settlement agreement provides for annual recovery of additional spent fuel storage and related costs incurred from 2011 through 2013 with the ability to extend the recovery period as mutually agreed to by the parties. The parties have agreed in principle to extend the recovery period through 2016. As a result of the settlement agreement, Ameren Missouri recorded a pretax reduction of $2 million and $2 million to its “Operating Expenses – Depreciation and amortization” and “Operating Expenses – Other operations and maintenance” expense line items, respectively, on its statement of income for the year ended December 31, 2011. In 2012, Ameren Missouri received a 2011 cost reimbursement of $1 million and reduced its "Property and plant, net" assets on its balance sheet by that amount. In 2013, Ameren Missouri received a 2012 cost reimbursement of $6 million and reduced its "Property and plant, net" assets on its balance sheet by that amount. In March 2014, Ameren Missouri plans to submit approximately $15 million of 2013 costs to the DOE for reimbursement pursuant to the settlement agreement. Ameren Missouri reduced its "Property and plant, net" assets by this amount with an offset to "Miscellaneous accounts and notes receivable" on its balance sheet as of December 31, 2013. Included in these reimbursements are costs related to a dry spent fuel storage facility Ameren Missouri is constructing at its Callaway energy center. Ameren Missouri intends to begin transferring spent fuel assemblies to this facility in 2015. Until the facility is completed, Ameren Missouri will, in accordance with the settlement agreement, apply for reimbursement from the DOE for the cost to construct the dry spent fuel storage facility along with related allowable costs.
	In December 2011, Ameren Missouri submitted a license extension application to the NRC to extend its Callaway energy center's operating license from 2024 to 2044. There is no deadline by which the NRC must act on this application. Among the rules that the NRC has historically relied upon in approving license extensions are rules dealing with the storage of spent nuclear fuel at the reactor site and with the NRC's confidence that permanent disposal of spent nuclear fuel will be available when needed. In a June 2012 decision, the United States Court of Appeals for the District of Columbia Circuit vacated these rules and remanded the case to the NRC, holding that the NRC's obligations under the National Environmental Policy Act required a more thorough environmental analysis in support of the NRC's waste confidence decision. In June 2012, a number of groups petitioned the NRC to suspend final licensing decisions in certain NRC licensing proceedings, including the Callaway license extension, until the NRC completed its proceedings on the vacated rules. In August 2012, the NRC stated that it would not issue licenses dependent on the vacated rules until it appropriately addressed the court's remand. In September 2012, the NRC directed its staff to issue, within two years, a generic environmental impact statement and a final rule to address the court's ruling. The NRC also stated that a site-specific analysis of these issues could be conducted in rare circumstances. If the Callaway energy center's license is extended, additional spent fuel storage will be required.
	Electric utility rates charged to customers provide for the recovery of the Callaway energy center's decommissioning costs, which include decontamination, dismantling, and site restoration costs, over an assumed 40-year life of the nuclear center, ending with the expiration of the energy center's current operating license in 2024. It is assumed that the Callaway energy center site will be decommissioned through the immediate dismantlement method and removed from service. Ameren and Ameren Missouri have recorded an ARO for the Callaway energy center decommissioning costs at fair value, which represents the present value of estimated future cash outflows. Decommissioning costs are included in the costs of service used to establish electric rates for Ameren Missouri's customers. These costs amounted to $7 million in each of the years 2013, 2012, and 2011. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway energy center. Electric rates may be adjusted at such times to reflect changed estimates. The last cost study and funding analysis were filed with the MoPSC in September 2011. In October 2012, the MoPSC issued an order approving the stipulation and agreement between Ameren Missouri and the MoPSC staff that maintained the current rate of deposits to the trust fund and the rate of return assumptions used in the analysis. If Ameren Missouri's operating license extension application is approved by the NRC, a revised funding analysis will be prepared, and the rates charged to customers will be adjusted accordingly to reflect the operating license extension at the time the next triennial cost study and funding analysis is approved by the MoPSC. Amounts collected from customers are deposited in an external trust fund to provide for the Callaway energy center's decommissioning. If the assumed return on trust assets is not earned, we believe that it is probable that any such earnings deficiency will be recovered in rates. The fair value of the nuclear decommissioning trust fund for Ameren Missouri's Callaway energy center is reported as "Nuclear decommissioning trust fund" in Ameren's and Ameren Missouri's balance sheets. This amount is legally restricted and may be used only to fund the costs of nuclear decommissioning. Changes in the fair value of the trust fund are recorded as an increase or decrease to the nuclear decommissioning trust fund, with an offsetting adjustment to the related regulatory liability.
	See Note 2 – Rate and Regulatory Matters and Note 9 – Nuclear Decommissioning Trust Fund Investments for additional information related to the Callaway energy center.

Retirement_Benefits

Retirement Benefits	12 Months Ended
	Dec. 31, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
RETIREMENT BENEFITS	'
	RETIREMENT BENEFITS
	The primary objective of the Ameren pension and postretirement benefit plans is to provide eligible employees with pension and postretirement health care and life insurance benefits. Ameren offers defined benefit pension and postretirement benefit plans covering substantially all of its employees. Ameren uses a measurement date of December 31 for its pension and postretirement benefit plans. Ameren Missouri and Ameren Illinois each participate in Ameren’s single-employer pension and other postretirement plans. Ameren’s qualified pension plan is the Ameren Retirement Plan. Ameren also has an unfunded nonqualified pension plan, the Ameren Supplemental Retirement Plan, which is available for certain management employees and retirees to provide a supplemental benefit when their qualified pension plan benefits are capped to comply with Internal Revenue Code limitations. Ameren’s other postretirement plans are the Ameren Retiree Medical Plan and the Ameren Group Life Insurance Plan. Nonaffiliated Ameren companies do not participate in the Ameren Retirement Plan, the Ameren Supplemental Retirement Plan, the Ameren Retiree Medical Plan, or the Ameren Group Life Insurance Plan.
	On December 2, 2013, Ameren completed the divestiture of New AER to IPH. In accordance with the transaction agreement, Ameren retained the pension obligations as of December 2, 2013, associated with the current and former employees of New AER and its subsidiaries who were included in the Ameren Retirement Plan and the Ameren Supplemental Retirement Plan. Ameren also retained the postretirement benefit obligations associated with the employees of New AER and its subsidiaries who were eligible to retire at December 2, 2013, from the Ameren Retiree Medical Plan and the Ameren Group Life Insurance Plan. IPH assumed the existing pension and other postretirement benefit obligations associated with EEI's current and former employees that are included in EEI’s single-employer pension and other postretirement plans. Coincident with Ameren’s divestiture of New AER, a significant number of employees left Ameren which required a measurement of Ameren’s pension and postretirement benefit plan assets and obligations as of December 2, 2013, based upon current market conditions. The reduction in obligations for the postretirement benefit plans and the accelerated recognition of gains previously recorded in accumulated other comprehensive income that had not previously been recognized through net periodic benefit cost for the pension and postretirement benefit plans resulted in a $19 million pretax curtailment gain, which was included in discontinued operations.
	Ameren completed another measurement as of December 31, 2013, as is its historical accounting practice, based upon the market conditions at the end of the year. Excluding the EEI plans, which were assumed by IPH during 2013, Ameren’s unfunded obligation under its pension and other postretirement benefit plans was $461 million and $1,143 million as of December 31, 2013, and December 31, 2012, respectively. These net liabilities are recorded in "Other current liabilities," "Pension and other postretirement benefits," and "Other assets" on Ameren's consolidated balance sheet. The primary factors contributing to this unfunded obligation reduction during 2013 were a 75 basis point increase in the pension and other postretirement benefit plan discount rates used to determine the present value of the obligations, and asset returns being better than expected. The offset to the unfunded obligation reduction was primarily a reduction to "Regulatory assets" on Ameren's consolidated balance sheet.
	The following table presents the net benefit liability recorded on the balance sheets of each of the Ameren Companies as of December 31, 2013, and 2012:
		2013			2012
	Ameren(a)	$	461		$	1,143
	Ameren Missouri	191			464
	Ameren Illinois	198			408
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
	Ameren recognizes the under-funded status of its pension and postretirement plans as a liability on its consolidated balance sheet, with offsetting entries to accumulated OCI and regulatory assets, in accordance with authoritative accounting guidance. The following table presents the funded status of our pension and postretirement benefit plans as of December 31, 2013, and 2012. It also provides the amounts included in regulatory assets and accumulated OCI at December 31, 2013, and 2012, that have not been recognized in net periodic benefit costs.
		2013							2012
		Pension Benefits(a)				Postretirement			Pension Benefits(a)				Postretirement
						Benefits(a)							Benefits(a)
	Accumulated benefit obligation at end of year	$	3,698		$	(b)			$	3,829		$	(b)
	Change in benefit obligation:
	Net benefit obligation at beginning of year	$	4,051		$	1,157			$	3,764		$	1,145
	Service cost	91				22			81				22
	Interest cost	163				46			166				47
	Participant contributions	—				16			—				16
	Actuarial (gain) loss	(207		)		(76	)		240				(10	)
	Curtailment gain(c)	—				(3	)		—				—
	Settlement(d)	—				(5	)		—				—
	Benefits paid	(198		)		(64	)		(200		)		(69	)
	Early retiree reinsurance program receipt	(b)				—			(b)				2
	Federal subsidy on benefits paid	(b)				3			(b)				4
	Net benefit obligation at end of year	3,900				1,096			4,051				1,157
	Change in plan assets:
	Fair value of plan assets at beginning of year	3,127				938			2,814				836
	Actual return on plan assets	376				156			385				104
	Employer contributions	156				25			128				45
	Federal subsidy on benefits paid	(b)				3			(b)				4
	Early retiree reinsurance program receipt	(b)				—			(b)				2
	Participant contributions	—				16			—				16
	Benefits paid	(198		)		(64	)		(200		)		(69	)
	Fair value of plan assets at end of year	3,461				1,074			3,127				938
	Funded status – deficiency	439				22			924				219
	Accrued benefit cost at December 31	$	439		$	22			$	924		$	219
	Amounts recognized in the balance sheet consist of:
	Noncurrent asset(e)	$	—		$	(9	)		$	—		$	—
	Current liability(f)	3				1			3				2
	Noncurrent liability	436				30			921				217
	Net liability recognized	$	439		$	22			$	924		$	219
	Amounts recognized in regulatory assets consist of:
	Net actuarial (gain) loss	$	282		$	(71	)		$	699		$	103
	Prior service cost (credit)	(7		)		(20	)		(6		)		(24	)
	Amounts (pretax) recognized in accumulated OCI consist of:
	Net actuarial (gain) loss	17				(12	)		65				5
	Prior service cost (credit)	—				(1	)		(14		)		(6	)
	Total	$	292		$	(104	)		$	744		$	78
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
	(b)	Not applicable.
	(c)	Effective with the divestiture of New AER on December 2, 2013, the liability for active management employees of New AER and its subsidiaries not eligible to retire were neither transferred to IPH nor retained by Ameren, which resulted in a curtailment gain. See Note 16 – Divestiture Transactions and Discontinued Operations for further information on the divestiture.
	(d)	Effective with the divestiture of New AER on December 2, 2013, the liability for active union employees of New AER and its subsidiaries not eligible to retire was transferred to IPH based on the assumption of the collective bargaining agreements in place, which resulted in a settlement. See Note 16 – Divestiture Transactions and Discontinued Operations for further information on the divestiture.
	(e)	Included in "Other assets" on Ameren's consolidated balance sheet.
	(f)	Included in "Other current liabilities" on Ameren's consolidated balance sheet.
	The following table presents the assumptions used to determine our benefit obligations at December 31, 2013, and 2012:
		Pension Benefits						Postretirement Benefits
		2013			2012			2013			2012
	Discount rate at measurement date	4.75	%		4	%		4.75	%		4	%
	Increase in future compensation	3.5			3.5			3.5			3.5
	Medical cost trend rate (initial)	—			—			5			5
	Medical cost trend rate (ultimate)	—			—			5			5
Years to ultimate rate	—			—			—			—
Ameren determines discount rate assumptions by identifying a theoretical settlement portfolio of high-quality corporate bonds sufficient to provide for a plan's projected benefit payments, pursuant to authoritative accounting guidance on the determination of discount rates used for defined benefit plan obligations. The settlement portfolio of bonds is selected from a pool of over 500 high-quality corporate bonds.  A single discount rate is then determined; that rate results in a discounted value of the plan's benefit payments that equates to the market value of the selected bonds.
Funding
Pension benefits are based on the employees’ years of service and compensation. Ameren’s pension plan is funded in compliance with income tax regulations and federal funding or regulatory requirements. As a result, Ameren expects to fund its pension plan at a level equal to the greater of the pension expense or the legally required minimum contribution. Considering its assumptions at December 31, 2013, its investment performance in 2013, and its pension funding policy, Ameren expects to make annual contributions of $20 million to $100 million in each of the next five years, with aggregate estimated contributions of $270 million. We expect Ameren Missouri’s and Ameren Illinois’ portion of the future funding requirements to be 52%, and 47%, respectively. These amounts are estimates. They may change based on actual investment performance, changes in interest rates, changes in our assumptions, changes in government regulations, and any voluntary contributions. Our funding policy for postretirement benefits is primarily to fund the Voluntary Employee Beneficiary Association (VEBA) trusts to match the annual postretirement expense.
The following table presents the cash contributions made to our defined benefit retirement plan and to our postretirement plans during 2013, 2012, and 2011:
	Pension Benefits												Postretirement Benefits
	2013				2012				2011				2013				2012		2011
Ameren Missouri	$	60			$	52			$	43			$	10			$	9	$	9
Ameren Illinois	50				46				28				11				35		118
Other	46				30				25				4				1		2
Ameren(a)	156				128				96				25				45		129
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Investment Strategy and Policies
Ameren manages plan assets in accordance with the “prudent investor” guidelines contained in ERISA. The investment committee, to the extent authority is delegated to it by the finance committee of Ameren’s board of directors, implements investment strategy and asset allocation guidelines for the plan assets. The investment committee includes members of senior management. The investment committee’s goals are twofold: first, to ensure that sufficient funds are available to provide the benefits at the time they are payable; second, to maximize total return on plan assets and minimize expense volatility consistent with its tolerance for risk. Ameren delegates investment management to specialists in each asset class. As appropriate, Ameren provides the investment manager with guidelines that specify allowable and prohibited investment types. The investment committee regularly monitors manager performance and compliance with investment guidelines.
The expected return on plan assets assumption is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Projected rates of return for each asset class were estimated after an analysis of historical experience, future expectations, and the volatility of the various asset classes. After considering the target asset allocation for each asset class, we adjusted the overall expected rate of return for the portfolio for historical and expected experience of active portfolio management results compared with benchmark returns and for the effect of expenses paid from plan assets. Ameren will use an expected return on plan assets for its pension plan assets and postretirement plan assets of 7.25% and 7.00%, respectively, in 2014. No plan assets are expected to be returned to Ameren during 2014.
Ameren’s investment committee strives to assemble a portfolio of diversified assets that does not create a significant concentration of risks. The investment committee develops asset allocation guidelines between asset classes, and it creates diversification through investments in assets that differ by type (equity, debt, real estate, private equity), duration, market capitalization, country, style (growth or value) and industry, among other factors. The diversification of assets is displayed in the target allocation table below. The investment committee also routinely rebalances the plan assets to adhere to the diversification goals. The investment committee’s strategy reduces the concentration of investment risk; however, Ameren is still subject to overall market risk. The following table presents our target allocations for 2014 and our pension and postretirement plans’ asset categories as of December 31, 2013, and 2012.
Asset	Target Allocation		Percentage of Plan Assets at December  31,
Category	2014		2013			2012
Pension Plan:
Cash and cash equivalents	0 - 5  %		2	%		2	%
Equity securities:
U.S. large capitalization	29 - 39		36			34	%
U.S. small and mid-capitalization	2 - 12		8			7	%
International and emerging markets	9 - 19		14			13	%
Total equity	50 - 60		58			54	%
Debt securities	35 - 45		36			39	%
Real estate	0 -   9		4			4	%
Private equity	0 -   4		(a)			1	%
Total			100	%		100	%
Postretirement Plans:
Cash and cash equivalents	0 - 10 %		4	%		4	%
Equity securities:
U.S. large capitalization	33 - 43		41	%		40	%
U.S. small and mid-capitalization	3 - 13		8	%		8	%
International	10 - 20		14	%		14	%
Total equity	55 - 65		63	%		62	%
Debt securities	30 - 40		33	%		34	%
Total			100	%		100	%
(a)	Less than 1% of plan assets.
In general, the United States large capitalization equity investments are passively managed or indexed, whereas the international, emerging markets, United States small capitalization, and United States mid-capitalization equity investments are actively managed by investment managers. Debt securities include a broad range of fixed income vehicles. Debt security investments in high-yield securities, emerging market securities, and non-United States dollar-denominated securities are owned by the plans, but in limited quantities to reduce risk. Most of the debt security investments are under active management by investment managers. Real estate investments include private real estate vehicles; however, Ameren does not, by policy, hold direct investments in real estate property. Ameren’s investment in private equity funds consists of 9 different limited partnerships, with invested capital ranging from $0.1 million to $5 million each, which invest primarily in a diversified number of small United States-based companies. No further commitments may be made to private equity investments without approval by the finance committee of the board of directors. Additionally, Ameren’s investment committee allows investment managers to use derivatives, such as index futures, exchange traded funds, foreign exchange futures, and options, in certain situations, to increase or to reduce market exposure in an efficient and timely manner.
Fair Value Measurements of Plan Assets
Investments in the pension and postretirement benefit plans were stated at fair value as of December 31, 2013. The fair value of an asset is the amount that would be received upon sale in an orderly transaction between market participants at the measurement date. Cash and cash equivalents have initial maturities of three months or less and are recorded at cost plus accrued interest. The carrying amounts of cash and cash equivalents approximate fair value because of the short-term nature of these instruments. Investments traded in active markets on national or international securities exchanges are valued at closing prices on the last business day on or before the measurement date. Securities traded in over-the-counter markets are valued based on quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Derivative contracts are valued at fair value, as determined by the investment managers (or independent third parties on behalf of the investment managers), who use proprietary models and take into consideration exchange quotations on underlying instruments, dealer quotations, and other market information. The fair value of real estate is based on annual appraisal reports prepared by an independent real estate appraiser.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2013:
	Quoted Prices in				Significant Other				Significant Other				Total
	Active Markets for				Observable Inputs				Unobservable
	Identified Assets				(Level 2)				Inputs
	(Level 1)								(Level 3)
Cash and cash equivalents	$	5			$	39			$	—			$	44
Equity securities:
U.S. large capitalization	107				1,162				—				1,269
U.S. small and mid-capitalization	273				—				—				273
International and emerging markets	143				372				—				515
Debt securities:
Corporate bonds	—				860				—				860
Municipal bonds	—				149				—				149
U.S. treasury and agency securities	—				256				—				256
Other	—				27				—				27
Real estate	—				—				131				131
Private equity	—				—				15				15
Derivative assets	1				—				—				1
Derivative liabilities	(1		)		—				—				(1		)
Total	$	528			$	2,865			$	146			$	3,539
Less: Medical benefit assets at December 31(a)													(112		)
Plus: Net receivables at December 31(b)													34
Fair value of pension plans assets at year end													$	3,461
(a)	Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(b)	Receivables related to pending security sales, offset by payables related to pending security purchases.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2012:
	Quoted Prices in				Significant Other				Significant Other				Total
	Active Markets for				Observable Inputs				Unobservable
	Identified Assets				(Level 2)				Inputs
	(Level 1)								(Level 3)
Cash and cash equivalents	$	1			$	28			$	—			$	29
Equity securities:
U.S. large capitalization	83				1,007				—				1,090
U.S. small and mid-capitalization	235				—				—				235
International and emerging markets	134				301				—				435
Debt securities:
Corporate bonds	—				832				—				832
Municipal bonds	—				176				—				176
U.S. treasury and agency securities	—				250				—				250
Other	—				17				—				17
Real estate	—				—				118				118
Private equity	—				—				19				19
Derivative assets	—				—				—				—
Derivative liabilities	(1		)		—				—				(1		)
Total	$	452			$	2,611			$	137			$	3,200
Less: Medical benefit assets at December 31(a)													(102		)
Plus: Net receivables at December 31(b)													29
Fair value of pension plans assets at year end													$	3,127
(a)	Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(b)	Receivables related to pending security sales, offset by payables related to pending security purchases.
The following table summarizes the changes in the fair value of the pension plan assets classified as Level 3 in the fair value hierarchy for each of the years ended December 31, 2013, and 2012:
	Beginning				Actual Return on				Actual Return on				Purchases,				Net		Ending Balance at
	Balance at				Plan Assets Related				Plan Assets Related				Sales, and				Transfers		December 31,
	January 1,				to Assets Still Held				to Assets Sold				Settlements, Net				into (out of)
					at the Reporting Date				During the Period								of Level 3
2013:00:00
Real estate	$	118			$	9			$	—			$	4			$	—	$	131
Private equity	19				(9		)		11				(6		)		—		15
2012:00:00
Real estate	$	108			$	7			$	—			$	3			$	—	$	118
Private equity	23				(7		)		8				(5		)		—		19
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2013:
	Quoted Prices in				Significant Other				Significant Other				Total
	Active Markets for				Observable Inputs				Unobservable
	Identified Assets				(Level 2)				Inputs
	(Level 1)								(Level 3)
Cash and cash equivalents	$	77			$	—			$	—			$	77
Equity securities:
U.S. large capitalization	297				101				—				398
U.S. small and mid-capitalization	77				—				—				77
International	39				96				—				135
Debt securities:
Corporate bonds	—				89				—				89
Municipal bonds	—				103				—				103
U.S. treasury and agency securities	—				72				—				72
Asset-backed securities	—				10				—				10
Other	—				40				—				40
Total	$	490			$	511			$	—			$	1,001
Plus: Medical benefit assets at December 31(a)													112
Less: Net payables at December 31(b)													(39		)
Fair value of postretirement benefit plans assets at year end													$	1,074
(a)	Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(b)	Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2012:
	Quoted Prices in				Significant Other				Significant Other				Total
	Active Markets for				Observable Inputs				Unobservable
	Identified Assets				(Level 2)				Inputs
	(Level 1)								(Level 3)
Cash and cash equivalents	$	83			$	—			$	—			$	83
Equity securities:
U.S. large capitalization	245				88				—				333
U.S. small and mid-capitalization	66				—				—				66
International	45				69				—				114
Debt securities:
Corporate bonds	—				88				—				88
Municipal bonds	—				91				—				91
U.S. treasury and agency securities	—				67				—				67
Asset-backed securities	—				18				—				18
Other	—				22				—				22
Total	$	439			$	443			$	—			$	882
Plus: Medical benefit assets at December 31(a)													102
Less: Net payables at December 31(b)													(46		)
Fair value of postretirement benefit plans assets at year end													$	938
(a)	Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(b)	Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.
Net Periodic Benefit Cost
The following table presents the components of the net periodic benefit cost of our pension and postretirement benefit plans during 2013, 2012, and 2011:
	Pension Benefits				Postretirement Benefits
	Ameren(a)				Ameren(a)
2013
Service cost	$	91			$	22
Interest cost	163				46
Expected return on plan assets	(218		)		(62		)
Amortization of:
Transition obligation	—				—
Prior service cost	(2		)		(6		)
Actuarial loss	87				8
Curtailment gain	(12		)		(7		)
Net periodic benefit cost(b)	$	109			$	1
2012
Service cost	$	81			$	22
Interest cost	166				47
Expected return on plan assets	(208		)		(56		)
Amortization of:
Transition obligation	—				2
Prior service cost	(3		)		(6		)
Actuarial loss	75				5
Net periodic benefit cost(c)	$	111			$	14
2011
Service cost	$	73			$	20
Interest cost	175				54
Expected return on plan assets	(211		)		(50		)
Amortization of:
Transition obligation	—				2
Prior service cost	(1		)		(6		)
Actuarial loss	41				3
Net periodic benefit cost(c)	$	77			$	23
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)	The net periodic benefit cost includes a $6 million and a $7 million net gain for pension benefits and postretirement benefits, respectively, which was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). This net gain includes the curtailment gain recognized in 2013 as a result of a significant reduction in employees as of the December 2, 2013 closing date of the New AER divestiture. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.
(c)	The net periodic benefit cost includes $9 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2012 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). The net periodic benefit cost includes $7 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2011 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.
The current year expected return on plan assets is determined primarily by adjusting the prior-year market-related asset value for current year contributions, disbursements, and expected return, plus 25% of the actual return in excess of (or less than) expected return for the four prior years.
The estimated amounts that will be amortized from regulatory assets and accumulated OCI into net periodic benefit cost in 2014 are as follows:
	Pension Benefits				Postretirement Benefits
	Ameren(a)				Ameren(a)
Regulatory assets:
Prior service cost (credit)	$	(1	)		$	(4	)
Net actuarial loss	60				9
Accumulated OCI:
Net actuarial (gain) loss	1				(2		)
Total	$	60			$	3
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Prior service cost is amortized on a straight-line basis over the average future service of active participants benefiting under the plan amendment. The net actuarial (gain) loss subject to amortization is amortized on a straight-line basis over 10 years.
The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred and included in continuing operations for the years ended December 31, 2013, 2012, and 2011:
	Pension Costs												Postretirement Costs
	2013				2012				2011				2013				2012		2011
Ameren Missouri	$	69			$	63			$	51			$	8			$	10	$	11
Ameren Illinois	41				37				16				—				4		11
Other	5				2				3				—				—		1
Ameren(a)	115				102				70				8				14		23
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
The expected pension and postretirement benefit payments from qualified trust and company funds and the federal subsidy for postretirement benefits related to prescription drug benefits, which reflect expected future service, as of December 31, 2013, are as follows:
	Pension Benefits								Postretirement Benefits
	Paid from				Paid from				Paid from				Paid from				Federal
	Qualified				Company				Qualified				Company				Subsidy
	Trust				Funds				Trust				Funds
2014	$	247			$	3			$	61			$	2			$	3
2015	249				3				63				2				4
2016	255				3				66				2				4
2017	260				3				69				2				4
2018	264				3				72				2				4
2019 - 2023	1,342				14				394				12				19
The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2013, 2012, and 2011:
	Pension Benefits									Postretirement Benefits
	2013			2012			2011			2013			2012			2011
Discount rate at measurement date	4	%		4.5	%		5.25	%		4	%		4.5	%		5.25	%
Expected return on plan assets	7.5			7.75			8			7.25			7.5			7.75
Increase in future compensation	3.5			3.5			3.5			3.5			3.5			3.5
Medical cost trend rate (initial)	—			—			—			5			5.5			6
Medical cost trend rate (ultimate)	—			—			—			5			5			5
Years to ultimate rate	—			—			—			—			1 year			2 years
The table below reflects the sensitivity of Ameren’s plans to potential changes in key assumptions:
	Pension Benefits								Postretirement Benefits
	Service Cost				Projected				Service Cost				Postretirement
	and Interest				Benefit				and Interest				Benefit
	Cost				Obligation				Cost				Obligation
0.25% decrease in discount rate	$	(2	)		$	109			$	—			$	32
0.25% increase in salary scale	2				17				—				—
1.00% increase in annual medical trend	—				—				2				40
1.00% decrease in annual medical trend	—				—				(2		)		(37		)
Other
Ameren sponsors a 401(k) plan for eligible employees. The Ameren 401(k) plan covered all eligible employees at December 31, 2013. The plan allowed employees to contribute a portion of their compensation in accordance with specific guidelines. Ameren matched a percentage of the employee contributions up to certain limits. The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to the continuing operations for each of the Ameren Companies for the years ended December 31, 2013, 2012, and 2011:
	2013				2012				2011
Ameren Missouri	$	16			$	16			$	16
Ameren Illinois	10				9				8
Other	1				1				1
Ameren(a)	27				26				25
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
STOCK-BASED COMPENSATION	'
	STOCK-BASED COMPENSATION
	Ameren’s long-term incentive plan available for eligible employees is the shareholder-approved 2006 Omnibus Incentive Compensation Plan (2006 Plan), which became effective May 2, 2006. The 2006 Plan provides for a maximum of 4 million common shares to be available for grant to eligible employees and directors. The 2006 Plan awards may be stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance share units, cash-based awards, and other stock-based awards.
	A summary of nonvested shares at December 31, 2013, and changes during the year ended December 31, 2013, under the 2006 Plan are presented below:
		Performance Share Units
		Share		Weighted-average
		Units		Fair Value per Unit
	Nonvested at January 1, 2013	1,192,487		$	33.56
	Granted(a)	840,482		31.19
	Unearned or forfeited(b)	(29,730	)	31.93
	Earned and vested(c)	(784,695	)	31.6
	Nonvested at December 31, 2013	1,218,544		$	33.23
	(a)	Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2013 under the 2006 Plan.
	(b)	Includes share units granted in 2011 that were not earned based on performance provisions of the award grants.
	(c)	Includes share units granted in 2011 that vested as of December 31, 2013, that were earned pursuant to the provisions of the award grants. Also includes share units that vested due to attainment of retirement eligibility by certain employees and certain employees whose employment terminated on December 2, 2013, with the divestiture of New AER. Actual shares issued for retirement-eligible employees and former New AER subsidiaries' employees will vary depending on actual performance over the three-year measurement period.
	Ameren recorded compensation expense of $20 million, $22 million, and $13 million for the years ended December 31, 2013, 2012, and 2011, respectively, and a related tax benefit of $8 million, $8 million and $5 million for the years ended December 31, 2013, 2012, and 2011, respectively. Ameren settled performance share units and restricted shares of $11 million, $11 million, and $4 million for the years ended December 31, 2013, 2012, and 2011. All outstanding restricted shares vested as of the end of 2011. There were no significant compensation costs capitalized related to the performance share units during the years ended December 31, 2013, 2012, and 2011. As of December 31, 2013, total compensation cost of $20 million related to nonvested awards not yet recognized is expected to be recognized over a weighted-average period of 20 months.
	Performance Share Units
	Performance share units have been granted under the 2006 Plan. A share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, certain specified performance or market conditions have been met and the individual remains employed by Ameren. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals.
	The fair value of each share unit awarded in January 2013 under the 2006 Plan was determined to be $31.19. That amount was based on Ameren's closing common share price of $30.72 at December 31, 2012, and lattice simulations. Lattice simulations are used to estimate expected share payout based on Ameren's total shareholder return for a three-year performance period relative to the designated peer group beginning January 1, 2013. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.36%, volatility of 12% to 21% for the peer group, and Ameren's attainment of a three-year average earnings per share threshold during the performance period.
	The fair value of each share unit awarded in January 2012 under the 2006 Plan was determined to be $35.68. That amount was based on Ameren’s closing common share price of $33.13 at December 31, 2011, and lattice simulations. Lattice simulations are used to estimate expected share payout based on Ameren’s total shareholder return for a three-year performance period relative to the designated peer group beginning January 1, 2012. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.41%, volatility of 17% to 31% for the peer group, and Ameren’s attainment of a three-year average earnings per share threshold during the performance period.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
INCOME TAXES	'
	INCOME TAXES
	The following table presents the principal reasons why the effective income tax rate differed from the statutory federal income tax rate for the years ended December 31, 2013, 2012, and 2011:
		Ameren Missouri			Ameren Illinois			Ameren
	2013
	Statutory federal income tax rate:	35	%		35	%		35	%
	Increases (decreases) from:
	Depreciation differences	—			(1	)		—
	Amortization of investment tax credit	(1	)		—			(1	)
	State tax	3			6			4
	Other permanent items(a)	1			—			—
	Effective income tax rate	38	%		40	%		38	%
	2012
	Statutory federal income tax rate:	35	%		35	%		35	%
	Increases (decreases) from:
	Depreciation differences	(1	)		—			(1	)
	Amortization of investment tax credit	(1	)		(1	)		(1	)
	State tax	3			6			5
	Reserve for uncertain tax positions	1			—			—
	Other permanent items(a)	—			—			(1	)
	Effective income tax rate	37	%		40	%		37	%
	2011
	Statutory federal income tax rate:	35	%		35	%		35	%
	Increases (decreases) from:
	Depreciation differences	(2	)		—			(1	)
	Amortization of investment tax credit	(1	)		(1	)		(1	)
	State tax	3			5			4
	Reserve for uncertain tax positions	—			—			1
	Tax credits	—			—			(1	)
	Other permanent items(a)	1			—			—
	Effective income tax rate	36	%		39	%		37	%
	(a)	Permanent items are treated differently for book and tax purposes and primarily include non-taxable income related to company-owned life insurance and deductions related to dividends on DRPlus and the 401(k) plan for Ameren, as well as nondeductible expenses related to lobbying and stock issuance costs for Ameren Missouri.
	The following table presents the components of income tax expense (benefit) for the years ended December 31, 2013, 2012, and 2011:
		Ameren Missouri				Ameren Illinois				Other				Ameren(a)
	2013
	Current taxes:
	Federal	$	136			$	(15	)		$	(239	)	(b)	$	(118	)
	State	41				21				(43		)	(b)	19
	Deferred taxes:
	Federal	64				99				205			(b)	368
	State	6				6				36			(b)	48
	Deferred investment tax credits, amortization	(5		)		(1		)		—				(6		)
	Total income tax expense (benefit)	$	242			$	110			$	(41	)		$	311
	2012
	Current taxes:
	Federal	$	(25	)		$	(7	)		$	72			$	40
	State	(10		)		(3		)		23				10
	Deferred taxes:
	Federal	248				76				(120		)		204
	State	44				30				(14		)		60
	Deferred investment tax credits, amortization	(5		)		(2		)		—				(7		)
	Total income tax expense (benefit)	$	252			$	94			$	(39	)		$	307
	2011
	Current taxes:
	Federal	$	3			$	(24	)		$	15			$	(6	)
	State	2				(4		)		—				(2		)
	Deferred taxes:
	Federal	129				123				(39		)		213
	State	31				34				(10		)		55
	Deferred investment tax credits, amortization	(4		)		(2		)		—				(6		)
	Total income tax expense (benefit)	$	161			$	127			$	(34	)		$	254
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	These amounts are substantially related to the reversal of unrecognized tax benefits as a result of new IRS guidance related to the deductibility of expenditures to maintain, replace or improve steam or electric power generation property, along with casualty loss deductions for storm damage. They also reflect the increase in deferred tax expense due to available net operating losses.
	The Illinois corporate income tax rate increased from 7.3% to 9.5%, as of January 2011. The tax rate is scheduled to decrease to 7.75% in 2015, and it is scheduled to return to 7.3% in 2025. This corporate income tax rate increase in Illinois increased current income tax expense in 2011 by $6 million and $4 million for Ameren and Ameren Illinois, respectively. As a result of this corporate income tax rate increase, accumulated deferred tax balances were revalued, resulting in a decrease in deferred tax expense of $2 million and $3 million for Ameren and Ameren Illinois, respectively, in 2011.
The following table presents the deferred tax assets and deferred tax liabilities recorded as a result of temporary differences at December 31, 2013, and 2012:
	Ameren Missouri				Ameren Illinois				Other				Ameren(a)
2013
Accumulated deferred income taxes, net liability (asset):
Plant related	$	2,513			$	1,243			$	13			$	3,769
Regulatory assets, net	74				2				—				76
Deferred employee benefit costs	(74		)		(85		)		(114		)		(273		)
Purchase accounting	—				(27		)		(1		)		(28		)
ARO	(7		)		1				—				(6		)
Other(b)(c)	(17		)		(63		)		(398		)		(478		)
Total net accumulated deferred income tax liabilities (assets)(d)	$	2,489			$	1,071			$	(500	)		$	3,060
2012
Accumulated deferred income taxes, net liability (asset):
Plant related	$	2,385			$	1,145			$	20			$	3,550
Regulatory assets, net	73				—				—				73
Deferred employee benefit costs	(84		)		(102		)		(137		)		(323		)
Purchase accounting	—				(27		)		(1		)		(28		)
ARO	(7		)		1				—				(6		)
Other(b)	50				(77		)		(223		)		(250		)
Total net accumulated deferred income tax liabilities (assets)(e)	$	2,417			$	940			$	(341	)		$	3,016
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
(b)	Includes deferred tax assets related to net operating loss and tax credit carryforwards detailed in the table below.
(c)	Includes total valuation allowances for Ameren, Ameren Missouri, and Ameren Illinois of $7 million, $1 million, and $1 million, respectively, as of December 31, 2013. The state valuation allowances are shown in the table below.
(d)	Includes $20 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2013.
(e)	Includes $26 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2012.
The following table presents the components of deferred tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2013:
	Ameren Missouri				Ameren Illinois				Other				Ameren(a)
Net operating loss carryforwards:
Federal(b)	$	61			$	84			$	215			$	360
State(c)	3				11				34				48
Total net operating loss carryforwards	$	64			$	95			$	249			$	408
Tax credit carryforwards:
Federal(d)	$	12			$	—			$	76			$	88
State(e)	1				1				32				34
State valuation allowance(f)	(1		)		(1		)		(2		)		(4		)
Total tax credit carryforwards	$	12			$	—			$	106			$	118
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)	These will begin to expire in 2028.
(c)	These will begin to expire in 2017.
(d)	These will begin to expire in 2029.
(e)	These will begin to expire in 2014.
(f)	This balance increased by $2 million, $- million and $- million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2013.
The following table presents the components of deferred tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2012:
	Ameren Missouri				Ameren Illinois				Other				Ameren(a)
Net operating loss carryforwards:
Federal(b)	$	61			$	61			$	51			$	173
State(c)	3				11				13				27
Total net operating loss carryforwards	$	64			$	72			$	64			$	200
Tax credit carryforwards:
Federal(d)	$	11			$	—			$	75			$	86
State(e)	1				1				23				25
State valuation allowance(f)	(1		)		(1		)		—				(2		)
Total tax credit carryforwards	$	11			$	—			$	98			$	109
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)	These will begin to expire in 2028
(c)	These will begin to expire in2017.
(d)	These will begin to expire in 2029.
(e)	These began to expire in 2013.
(f)	This balance increased by $1 million, $- million and $1 million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2012.
Uncertain Tax Positions
A reconciliation of the change in the unrecognized tax benefit balance during the years ended December 31, 2011, 2012, and 2013, is as follows:
	Ameren Missouri				Ameren Illinois				Other				Ameren(a)
Unrecognized tax benefits – January 1, 2011	$	164			$	56			$	26			$	246
Increases based on tax positions prior to 2011	15				—				7				22
Decreases based on tax positions prior to 2011	(63		)		(41		)		(21		)		(125		)
Increases based on tax positions related to 2011	13				—				4				17
Changes related to settlements with taxing authorities	(5		)		(4		)		(1		)		(10		)
Decreases related to the lapse of statute of limitations	—				—				(2		)		(2		)
Unrecognized tax benefits – December 31, 2011	$	124			$	11			$	13			$	148
Increases based on tax positions prior to 2012	4				—				1				5
Decreases based on tax positions prior to 2012	(7		)		(1		)		(5		)		(13		)
Increases (decreases) based on tax positions related to 2012	15				3				(1		)		17
Changes related to settlements with taxing authorities	—				—				—				—
Decreases related to the lapse of statute of limitations	—				—				(1		)		(1		)
Unrecognized tax benefits – December 31, 2012	$	136			$	13			$	7			$	156
Increases based on tax positions prior to 2013	—				2				5				7
Decreases based on tax positions prior to 2013	(122		)		(16		)		(5		)		(143		)
Increases based on tax positions related to 2013	16				—				53			(b)	69
Changes related to settlements with taxing authorities	—				—				—				—
Increases related to the lapse of statute of limitations	1				—				—				1
Unrecognized tax benefits (detriments) – December 31, 2013	$	31			$	(1	)		$	60			$	90
Total unrecognized tax benefits that, if recognized, would affect the effective tax rates as of December 31, 2011	$	1			$	—			$	—			$	1
Total unrecognized tax benefits (detriments) that, if recognized, would affect the effective tax rates as of December 31, 2012	$	3			$	(1	)		$	(1	)		$	1
Total unrecognized tax benefits that, if recognized, would affect the effective tax rates as of December 31, 2013	$	3			$	—			$	51		(b)	$	54
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
(b)	Primarily due to tax positions relating to the New AER divestiture. The income statement impact of this unrecognized tax benefit was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information.
The Ameren Companies recognize interest charges (income) and penalties accrued on tax liabilities on a pretax basis as interest charges (income) or miscellaneous expense, respectively, in the statements of income.
A reconciliation of the change in the liability for interest on unrecognized tax benefits during the years ended December 31, 2011, 2012, and 2013, is as follows:
	Ameren Missouri				Ameren Illinois				Other				Ameren(a)
Liability for interest – January 1, 2011	$	10			$	2			$	5			$	17
Interest income for 2011	(3		)		(1		)		(7		)		(11		)
Interest payment	(1		)		—				—				(1		)
Liability for interest – December 31, 2011	$	6			$	1			$	(2	)		$	5
Interest charges (income) for 2012	2				—				(1		)		1
Liability for interest – December 31, 2012	$	8			$	1			$	(3	)		$	6
Interest charges (income) for 2013	(8		)		(1		)		4				(5		)
Liability for interest – December 31, 2013	$	—			$	—			$	1			$	1
(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
As of December 31, 2011, 2012, and 2013, the Ameren Companies have accrued no amount for penalties with respect to unrecognized tax benefits.
In 2011, a final settlement for the years 2005 and 2006 was reached with the IRS. It resulted in a reduction in uncertain tax liabilities of $39 million, $17 million and $12 million for Ameren, Ameren Missouri and Ameren Illinois, respectively. Ameren’s federal income tax returns for the years 2007 through 2011 are before the Appeals Office of the IRS. Ameren’s federal income tax return for the year 2012 is currently under examination.
It is reasonably possible that a settlement will be reached with the Appeals Office of the IRS in the next twelve months for the years 2007 through 2011. This settlement, primarily related to uncertain tax positions for capitalization versus currently deductible repair expense and research deductions, is expected to result in a decrease in uncertain tax benefits of approximately $20 million and $13 million for Ameren and Ameren Missouri, respectively. In addition, it is reasonably possible that other events will occur during the next twelve months that would cause the total amount of unrecognized tax benefits for the Ameren Companies to increase or decrease. However, the Ameren Companies do not believe any such increases or decreases, including the decrease from the reasonably possible IRS Appeals Office settlement discussed above, would be material to their results of operations, financial position, or liquidity.
In 2013, unrecognized tax benefits related to the deductibility of expenditures to maintain, replace, or improve steam or electric power generation property, along with casualty loss deductions for storm damage, were reduced by $103 million, $95 million and $5 million for Ameren, Ameren Missouri and Ameren Illinois, respectively. This reduction in unrecognized tax benefits did not impact overall income tax expense for the Ameren Companies. However, the liability for interest related to these unrecognized tax benefits has been released. In 2013, Ameren adopted an accounting method change as a result of the recent guidance issued by the IRS, establishing new rules for the amount and timing of the deductions to maintain, replace or improve generation property. In 2014, Ameren expects to adopt an accounting method change as a result of the recent guidance establishing new rules for the amount and timing of casualty loss deductions for storm damage.
State income tax returns are generally subject to examination for a period of three years after filing of the return. The state impact of any federal changes remains subject to examination by various states for a period of up to one year after formal notification to the states. The Ameren Companies do not currently have material state income tax issues under examination, administrative appeals, or litigation.
Ameren Missouri has an uncertain tax position tracker. Under Missouri's regulatory framework, uncertain tax positions do not reduce Ameren Missouri's electric rate base. When an uncertain income tax position liability is resolved, the MoPSC requires, through the uncertain tax position tracker, the creation of a regulatory asset or regulatory liability to reflect the time value, using the weighted-average cost of capital included in each of the electric rate orders in effect before the tax position was resolved, of the difference between the uncertain income tax position liability that was excluded from rate base and the final tax liability. The resulting regulatory asset or liability will affect earnings in the year it is created and then will be amortized over three years beginning on the effective date of new rates established in the next electric rate case.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
RELATED PARTY TRANSACTIONS	'
	RELATED PARTY TRANSACTIONS
	The Ameren Companies have engaged in, and may in the future engage in, affiliate transactions in the normal course of business. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between affiliates are reported as intercompany transactions on their financial statements, but are eliminated in consolidation for Ameren’s financial statements. Below are the material related party agreements.
	Electric Power Supply Agreements
	Capacity Supply Agreements
	Ameren Illinois, as an electric load-serving entity, must acquire capacity sufficient to meet its obligations to customers.
	In 2010, Ameren Illinois used an RFP process, administered by the IPA, to contract capacity for the period from June 1, 2010, through May 31, 2013. As a winning supplier in this process, in April 2010, Ameren Missouri contracted to supply a portion of Ameren Illinois’ capacity requirements for less than $1 million for the period from June 1, 2010, through May 31, 2013.
	In 2012, Ameren Illinois used an RFP process, administered by the IPA, to contract capacity for the period from June 1, 2012, through May 31, 2015. As a winning supplier in this process, in April 2012, Ameren Missouri contracted to supply a portion of Ameren Illinois' capacity requirements for $1 million and $3 million for the 12 months ending May 31, 2014, and 2015, respectively.
	Energy Swaps and Energy Products
	Ameren Illinois, as an electric load-serving entity, must acquire energy sufficient to meet its obligations to customers.
	In 2011, Ameren Illinois used an RFP process, administered by the IPA, to procure energy products that will settle physically from June 1, 2011, through May 31, 2014. Ameren Missouri was among the winning suppliers in the energy product RFP process. In May 2011, Ameren Missouri and Ameren Illinois entered into energy product agreements by which Ameren Missouri agreed to sell and Ameren Illinois agreed to purchase approximately 16,800 megawatthours at approximately $37 per megawatthour during the 12 months ending May 31, 2012, approximately 40,800 megawatthours at approximately $29 per megawatthour during the 12 months ending May 31, 2013, and approximately 40,800 megawatthours at approximately $28 per megawatthour during the 12 months ending May 31, 2014. The energy product agreements between Ameren Missouri and Ameren Illinois for the periods ending May 31, 2012, and May 31, 2013, were for off-peak hours only.
	Interconnection and Transmission Agreements
	Ameren Missouri and Ameren Illinois are parties to an interconnection agreement for the use of their respective transmission lines and other facilities for the distribution of power. These agreements have no contractual expiration date, but may be terminated by either party with three years’ notice.
	Joint Ownership Agreement
	ATXI and Ameren Illinois have a joint ownership agreement to construct, own, operate, and maintain certain electric transmission assets in Illinois. Under the terms of this agreement, Ameren Illinois and ATXI are responsible for their applicable share of all costs related to the construction, operation, and maintenance of electric transmission systems. Currently, there are no construction projects or joint ownership of existing assets under this agreement.
	In January 2011, ATXI repaid advances for the construction of transmission assets to Ameren Illinois in the amount of $52 million, including $3 million of accrued interest.
	In April 2011, ATXI transferred, at cost, all of ATXI’s construction work in progress assets related to a transmission line to Ameren Illinois for $20 million.
	Support Services Agreements
	Ameren Services provides support services to its affiliates. The costs of support services, including wages, employee benefits, professional services, and other expenses, are based on, or are an allocation of, actual costs incurred. The shared services support agreement can be terminated with respect to a particular affiliate by the mutual agreement of Ameren Services and that affiliate or by either Ameren Services or that affiliate with 60 days' notice before the end of a calendar year.
	In addition, Ameren Missouri and Ameren Illinois provide affiliates, primarily Ameren Services, with access to their facilities for administrative purposes. The cost of the rent and facility services are based on, or are an allocation of, actual costs incurred.
	Separately, Ameren Missouri and Ameren Illinois provide storm-related and miscellaneous support services to each other on an as-needed basis.
	Transmission Services
	Ameren Illinois must take transmission service from MISO for the retail load it serves in the AMIL pricing zone. ATXI is one of the transmission owners in the AMIL pricing zone. Accordingly ATXI receives transmission payments from Ameren Illinois through the MISO billing process.
	Money Pool
	See Note 4 – Short-term Debt and Liquidity and Note 5 – Long-term Debt and Equity Financings for a discussion of affiliate borrowing arrangements.
	Collateral Postings
	Under the terms of the Illinois power procurement agreements entered into through RFP processes administered by the IPA, suppliers must post collateral under certain market conditions to protect Ameren Illinois in the event of nonperformance. The collateral postings are unilateral, meaning that only the suppliers would be required to post collateral. Therefore, Ameren Missouri, as a winning supplier in the RFP process, may be required to post collateral. As of December 31, 2013, and 2012, there were no collateral postings required of Ameren Missouri related to the Illinois power procurement agreements.
	The following table presents the impact on Ameren Missouri and Ameren Illinois of related party transactions for the years ended December 31, 2013, 2012, and 2011. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity.
	Agreement	Income Statement Line Item			Ameren		Ameren
					Missouri		Illinois
	Ameren Missouri power supply agreements	Operating Revenues	2013	$	3	$	(a)
	with Ameren Illinois		2012		(b)		(a)
			2011		2		(a)
	Ameren Missouri and Ameren Illinois	Operating Revenues	2013		21		1
	rent and facility services		2012		19		1
			2011		16		2
	Ameren Missouri and Ameren Illinois	Operating Revenues	2013		1		3
	miscellaneous support services		2012		1		(b)
			2011		5		1
	Total Operating Revenues		2013	$	25	$	4
			2012		20		1
			2011		23		3
	Ameren Illinois power supply	Purchased Power	2013	$	(a)	$	3
	agreements with Ameren Missouri		2012		(a)		(b)
			2011		(a)		2
	Ameren Illinois transmission	Purchased Power	2013		(a)		2
	services with ATXI		2012		(a)		3
			2011		(a)		3
	Total Purchased Power		2013	$	(a)	$	5
			2012		(a)		3
			2011		(a)		5
	Ameren Services support services	Other Operations and	2013	$	116	$	93
	agreement	Maintenance	2012		106		88
			2011		114		87
	Insurance premiums(c)	Other Operations and	2013		(b)		(a)
		Maintenance	2012		(b)		(a)
			2011		(b)		(a)
	Total Other Operations and		2013	$	116	$	93
	Maintenance Expenses		2012		106		88
			2011		114		87
	Money pool borrowings (advances)	Interest (Charges)	2013	$	(b)	$	(b)
		Income	2012		(b)		(b)
			2011		—		—
	(a)	Not applicable.
(b)	Amount less than $1 million.
(c)	Represents insurance premiums paid to Energy Risk Assurance Company, an affiliate for replacement power, property damage, and terrorism coverage.

Commitments_And_Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
COMMITMENTS AND CONTINGENCIES	'
	COMMITMENTS AND CONTINGENCIES
	We are involved in legal, tax, and regulatory proceedings before various courts, regulatory commissions, authorities, and governmental agencies with respect to matters that arise in the ordinary course of business, some of which involve substantial amounts of money. We believe that the final disposition of these proceedings, except as otherwise disclosed in these notes to our financial statements, will not have a material adverse effect on our results of operations, financial position, or liquidity.
	See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 10 – Callaway Energy Center, Note 14 – Related Party Transactions, and Note 16 – Divestiture Transactions and Discontinued Operations in this report.
	Callaway Energy Center
	The following table presents insurance coverage at Ameren Missouri’s Callaway energy center at December 31, 2013. The property coverage and the nuclear liability coverage must be renewed on April 1 and January 1, respectively, of each year.
	Type and Source of Coverage	Maximum Coverages			Maximum Assessments
	Public liability and nuclear worker liability:
	American Nuclear Insurers	$	375		$	—
	Pool participation	13,241		(a)	128		(b)
		$	13,616	(c)	$	128
	Property damage:
	Nuclear Electric Insurance Limited	$	2,250	(d)	$	23	(e)
	European Mutual Association for Nuclear Insurance	500		(f)	—
		$	2,750		$	23
	Replacement power:
	Nuclear Electric Insurance Limited	$	490	(g)	$	9	(e)
	Missouri Energy Risk Assurance Company	$	64	(h)	$	—
	(a)	Provided through mandatory participation in an industrywide retrospective premium assessment program.
	(b)	Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $375 million in the event of an incident at any licensed United States commercial reactor, payable at $19 million per year.
	(c)	Limit of liability for each incident under the Price-Anderson Act liability provisions of the Atomic Energy Act of 1954, as amended. A company could be assessed up to $128 million per incident for each licensed reactor it operates with a maximum of $19 million per incident to be paid in a calendar year for each reactor. This limit is subject to change to account for the effects of inflation and changes in the number of licensed reactors.
	(d)	Nuclear Electric Insurance Limited provides $2.25 billion in property damage, decontamination, and premature decommissioning insurance. There is a $1.7 billion sublimit for non-radiation events, of which the top $200 million is a shared limit with other generators purchasing this coverage and includes one free reinstatement.
	(e)	All Nuclear Electric Insurance Limited insured plants could be subject to assessments should losses exceed the accumulated funds from Nuclear Electric Insurance Limited.
	(f)	European Mutual Association for Nuclear Insurance provides $500 million in excess of the $2.25 billion property coverage and $1.7 billion non-radiation coverage.
	(g)	Provides replacement power cost insurance in the event of a prolonged accidental outage at our nuclear energy center. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first eight weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Effective April 1, 2013, non-radiation events are sub-limited to $327.6 million.
	(h)	Provides replacement power cost insurance in the event of a prolonged accidental outage at our nuclear energy center. The coverage commences after the first 52 weeks of insurance coverage from Nuclear Electric Insurance Limited and is a weekly indemnity of $900,000 for 71 weeks in excess of the $3.6 million per week set forth above. Missouri Energy Risk Assurance Company LLC is an affiliate and has reinsured this coverage with third-party insurance companies. See Note 14 – Related Party Transactions for more information on this affiliate transaction.
	The Price-Anderson Act is a federal law that limits the liability for claims from an incident involving any licensed United States commercial nuclear energy center. The limit is based on the number of licensed reactors. The limit of liability and the maximum potential annual payments are adjusted at least every five years for inflation to reflect changes in the Consumer Price Index. The five-year inflationary adjustment was effective September 10, 2013. Owners of a nuclear reactor cover this exposure through a combination of private insurance and mandatory participation in a financial protection pool, as established by the Price-Anderson Act.
	Losses resulting from terrorist attacks are covered under Nuclear Electric Insurance Limited’s policies, subject to an industrywide aggregate policy limit of $3.24 billion within a 12-month period for coverage for such terrorist acts.
	If losses from a nuclear incident at the Callaway energy center exceed the limits of, or are not covered by insurance, or if coverage is unavailable, Ameren Missouri is at risk for any uninsured losses. If a serious nuclear incident were to occur, it could have a material adverse effect on Ameren’s and Ameren Missouri’s results of operations, financial position, or liquidity.
	Leases
	We lease various facilities, office equipment, plant equipment, and rail cars under capital and operating leases. The following table presents our lease obligations at December 31, 2013:
		Total			2014			2015		2016		2017		2018		After 5 Years
	Ameren:(a)
	Minimum capital lease payments(b)	$	556		$	32		$	33	$	33	$	33	$	32	$	393
	Less amount representing interest	257			27			27		27		27		26		123
	Present value of minimum capital lease payments	$	299		$	5		$	6	$	6	$	6	$	6	$	270
	Operating leases(c)	117			14			13		13		13		13		51
	Total lease obligations	$	416		$	19		$	19	$	19	$	19	$	19	$	321
	Ameren Missouri:
	Minimum capital lease payments(b)	$	556		$	32		$	33	$	33	$	33	$	32	$	393
	Less amount representing interest	257			27			27		27		27		26		123
	Present value of minimum capital lease payments	$	299		$	5		$	6	$	6	$	6	$	6	$	270
	Operating leases(c)	106			11			11		11		12		11		50
	Total lease obligations	$	405		$	16		$	17	$	17	$	18	$	17	$	320
	Ameren Illinois:
	Operating leases(c)	$	7		$	2		$	1	$	1	$	1	$	1	$	1
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	See Properties under Part I, Item 2, and Note 3 – Property and Plant, Net, of this report for additional information.
	(c)	Amounts related to certain land-related leases have indefinite payment periods. The annual obligation of $2 million, $1 million and $1 million for Ameren, Ameren Missouri and Ameren Illinois for these items is included in the 2014 through 2018 columns, respectively.
	The following table presents total rental expense, included in operating expenses, for the years ended December 31, 2013, 2012, and 2011:
		2013			2012			2011
	Ameren(a)	$	32		$	33		$	36
	Ameren Missouri	29			29			29
	Ameren Illinois	21			19			17
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	Other Obligations
	To supply a portion of the fuel requirements of our energy centers, we have entered into various long-term commitments for the procurement of coal, natural gas, nuclear fuel, and methane gas. We also have entered into various long-term commitments for purchased power and natural gas for distribution. The table below presents our estimated commitments at December 31, 2013. Ameren’s and Ameren Missouri’s purchased power obligations include a 102-megawatt power purchase agreement with a wind farm operator that expires in 2024. Ameren’s and Ameren Illinois’ purchased power obligations include the Ameren Illinois power purchase agreements entered into as part of the IPA-administered power procurement process. Included in the Other column are minimum purchase commitments under contracts for equipment, design and construction, and meter reading services at December 31, 2013. Ameren's and Ameren Illinois' Other column also include obligations related to IEIMA. In addition, the Other column includes Ameren's and Ameren Missouri's obligations related to energy efficiency programs under the MEEIA as approved by the MoPSC's December 2012 electric rate order. Ameren Missouri expects to incur $48 million in 2014 and $64 million in 2015 for these energy efficiency programs. See Note 2 – Rate and Regulatory Matters for additional information about the IEIMA and MEEIA.
		Coal			Natural			Nuclear		Purchased		Methane		Other		Total
					Gas(a)			Fuel		Power(b)		Gas
	Ameren:(c)
	2014	$	620		$	323		$	64	$	308	$	3	$	201	$	1,519
	2015	642			179			63		164		4		143		1,195
	2016	664			90			81		78		4		76		993
	2017	676			45			58		55		4		50		888
2018	120			28			57		52		5		51		313
Thereafter	125			82			158		635		91		350		1,441
Total	$	2,847		$	747		$	481	$	1,292	$	111	$	871	$	6,349
Ameren Missouri:
2014	$	620		$	62		$	64	$	19	$	3	$	127	$	895
2015	642			32			63		19		4		101		861
2016	664			19			81		19		4		40		827
2017	676			11			58		19		4		26		794
2018	120			8			57		19		5		27		236
Thereafter	125			28			158		110		91		183		695
Total	$	2,847		$	160		$	481	$	205	$	111	$	504	$	4,308
Ameren Illinois:
2014	$	—		$	261		$	—	$	289	$	—	$	23	$	573
2015	—			147			—		145		—		24		316
2016	—			71			—		59		—		24		154
2017	—			34			—		36		—		24		94
2018	—			20			—		33		—		24		77
Thereafter	—			54			—		525		—		167		746
Total	$	—		$	587		$	—	$	1,087	$	—	$	286	$	1,960
(a)	Includes amounts for generation and for distribution.
(b)	The purchased power amounts for Ameren and Ameren Illinois include 20-year agreements for renewable energy credits that were entered into in December 2010 with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.
(c)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
Ameren Illinois has entered into an agreement, through a process administered by the IPA, to purchase power from a repowered unit at the Meredosia energy center designed for permanent carbon dioxide capture and storage, annually over a 20-year period beginning in 2017, for its electric delivery service customers. The agreement is contingent on the parties interested in repowering the unit at the abandoned Meredosia energy center reaching certain milestones related to the construction and commencement of operations of this unit. Ameren will not repower the unit; however, a sale of the unit to a third party is possible. Construction has not begun on the unit at this energy center; therefore, Ameren Illinois’ obligations are not certain at this time and consequently not included in the table above. If the plant is not in service by 2019, Ameren Illinois can terminate the agreement.
Environmental Matters
We are subject to various environmental laws and regulations enforced by federal, state, and local authorities. From the beginning phases of siting and development to the ongoing operation of existing or new electric generation, transmission and distribution facilities and natural gas storage, transmission and distribution facilities, our activities involve compliance with diverse environmental laws and regulations. These laws and regulations address emissions, discharges to water, water usage, impacts to air, land, and water, and chemical and waste handling. Complex and lengthy processes are required to obtain and renew approvals, permits, or licenses for new, existing or modified facilities. Additionally, the use and handling of various chemicals or hazardous materials require release prevention plans and emergency response procedures.
The EPA is developing environmental regulations that will have a significant impact on the electric utility industry. Over time, compliance with these regulations could be particularly costly for certain companies, including Ameren Missouri, that operate coal-fired energy centers. Significant new rules proposed or promulgated include the regulation of CO2 emissions from new energy centers; revised national ambient air quality standards for ozone, fine particulates, SO2, and NOx emissions; the CSAPR, which would have required further reductions of SO2 emissions and NOx emissions from energy centers; a regulation governing management of CCR and coal ash impoundments; the MATS, which require reduction of emissions of mercury, toxic metals, and acid gases from energy centers; revised NSPS for particulate matter, SO2, and NOx emissions from new sources; new effluent standards applicable to waste water discharges from energy centers and new regulations under the Clean Water Act that could require significant capital expenditures, such as modifications to water intake structures or new cooling towers at our energy centers. The EPA is expected to propose CO2 standards for existing fossil fuel-fired electric generation units in the future. These new and proposed regulations, if adopted, may be challenged through litigation, so their ultimate implementation, as well as the timing of any such implementation, is uncertain. Although many details of these future regulations are unknown, the combined effects of the new and proposed environmental regulations may result in significant capital expenditures and increased operating costs over the next five to ten years for Ameren and Ameren Missouri. Compliance with these environmental laws and regulations could be prohibitively expensive or could result in the closure or alteration of the operation of some of our energy centers. Ameren and Ameren Missouri would expect these costs to be recoverable through rates, but the nature and timing of costs, as well as the applicable regulatory framework, could result in regulatory lag.
As of December 31, 2013, Ameren and Ameren Missouri estimate capital expenditure investments of $275 million to $350 million over the next five years to comply with existing environmental regulations. This estimate assumes that CCR will continue to be regulated as nonhazardous. This estimate does not include the impacts of regulations proposed by the EPA under the Clean Water Act, in March 2011, regarding cooling water intake structures or the impact of the effluent standards applicable to steam-electric generating units that the EPA proposed in April 2013, as the technology requirements of these final rules are not yet known. Considerable uncertainty remains in this estimate. The actual amount of capital expenditure investments to comply with existing environmental regulations may vary substantially from the above estimate due to uncertainty as to the precise compliance strategies that will be used and their ultimate cost, among other things.
Ameren Missouri's current environmental compliance plan for air emissions includes burning ultra-low-sulfur coal and installing new or optimizing existing pollution control equipment. Ameren Missouri has two scrubbers at its Sioux energy center, which are used to reduce SO2 emissions and other pollutants. Currently, Ameren Missouri's compliance plan assumes the installation of additional controls including mercury control technology and precipitator upgrades at multiple energy centers within its coal-fired fleet during the next five years. However, Ameren Missouri is currently evaluating its operations and options to determine how to comply with the MATS and other recently finalized or proposed EPA regulations. Additional controls may be necessary, depending upon the resolution of the CSAPR litigation currently pending before the United States Supreme Court or if a new rule replacing CAIR is ultimately adopted, as discussed below. If CSAPR is implemented, Ameren Missouri may be required to install two additional scrubbers within the next ten years.
Environmental compliance costs at some of Ameren Missouri's energy centers could be prohibitive and additional capital investment or continued operations unwarranted. Ameren Missouri's capital expenditures and other costs are subject to MoPSC prudence reviews, which could result in cost disallowances as well as regulatory lag.
The following sections describe the more significant environmental laws and rules that affect or could affect our operations.
Clean Air Act
Both federal and state laws require significant reductions in SO2 and NOx emissions that result from burning fossil fuels. In 2005, the EPA issued regulations with respect to SO2 and NOx emissions (the CAIR). In December 2008, the United States Court of Appeals for the District of Columbia Circuit found various aspects of the law to be unlawful and remanded the CAIR to the EPA for further action, but allowed the CAIR's cap-and-trade programs to remain effective until they are replaced by the EPA. In July 2011, the EPA issued the CSAPR as the CAIR replacement. The CSAPR regulations were vacated by the United States Court of Appeals for the District of Columbia Circuit. The EPA appealed to the United States Supreme Court, and a ruling is expected by June 2014. The EPA will continue to administer the CAIR until a new rule is ultimately adopted or until the United States Supreme Court overturns the decision to vacate the CSAPR.
In December 2011, the EPA issued the MATS under the Clean Air Act, which require emission reductions for mercury and other hazardous air pollutants, such as acid gases, toxic metals, and hydrogen chloride emissions. The MATS do not require a specific control technology to achieve the emission reductions. The MATS will apply to each unit at a coal-fired power plant; however in certain cases, emission compliance can be achieved by averaging emissions from similar electric generating units at the same power plant. Compliance is required by April 2015 or, with a case-by-case extension, by April 2016. Ameren Missouri's Labadie and Meramec energy centers requested and were granted extensions to April 2016 to comply with the MATS.
Emission Allowances
The Clean Air Act created marketable commodities called emission allowances under the acid rain program, the NOx budget trading program, and the CAIR. Ameren Missouri expects to have enough CAIR allowances for 2014 to avoid making external purchases to comply with these programs.
Greenhouse Gas Regulation
In December 2009, the EPA issued its “endangerment finding” under the Clean Air Act, which stated that greenhouse gas emissions, including CO2, endanger human health and welfare and that emissions of greenhouse gases from motor vehicles contribute to that endangerment. In March 2010, the EPA issued a determination that greenhouse gas emissions from stationary sources, such as power plants, would be subject to regulation under the Clean Air Act effective the beginning of 2011. As a result of these actions, we are required to consider the emissions of greenhouse gases in any air permit application.
Recognizing the difficulties presented by regulating at once virtually all emitters of greenhouse gases, the EPA issued the “Tailoring Rule,” which established new higher emission thresholds beginning in January 2011 for regulating greenhouse gas emissions from stationary sources, such as power plants. The rule requires any source that already has an operating permit to have greenhouse-gas-specific provisions added to its permits upon renewal. Currently, all Ameren energy centers have operating permits that have been modified to address greenhouse gas emissions. The Tailoring Rule also provides that if projects performed at major sources or new major sources result in an increase in emissions of greenhouse gases over an applicable annual threshold, such projects could trigger permitting requirements under the NSR programs and the application of best available control technology to control greenhouse gas emissions. In June 2012, the United States Court of Appeals for the District of Columbia Circuit upheld the Tailoring Rule. Industry groups and a coalition of states filed petitions in April 2013 requesting that the United States Supreme Court review the circuit court's decision. In October 2013, the United States Supreme Court granted limited review of one petition, agreeing to consider whether the Clean Air Act authorizes the EPA to regulate emissions of greenhouse gases from stationary sources, including power plants, as a result of its determination to regulate greenhouse gas emissions from motor vehicles. A ruling is expected in 2014.
In June 2013, the Obama administration announced that it had directed the EPA to set CO2 emissions standards for both new and existing power plants. The EPA published proposed regulations in January 2014 that would set revised CO2 emissions standards for new electricity generating units. The proposed standards would establish separate emissions limits for new natural gas-fired plants and new coal-fired plants. In addition, the Obama administration directed the EPA to propose a CO2 emissions standard for existing power plants by June 2014 and to finalize such standard by June 2015. Currently, the Ameren Companies are unable to predict the outcome or impacts of such future regulations.
Future federal and state legislation or regulations that mandate limits on the emission of greenhouse gases may result in significant increases in capital expenditures and operating costs, which, in turn, could lead to increased liquidity needs and higher financing costs. These compliance costs could be prohibitive at some of our energy centers, as the expected return from these investments, at current market prices for energy and capacity, might not justify the required capital expenditures or their continued operation, which could result in the impairment of long-lived assets if costs are not recovered through rates. To the extent that Ameren Missouri requests recovery of these costs through rates, its regulators might delay or deny timely recovery. Mandatory limits on the emission of greenhouse gases could increase costs for our customers or have a material adverse impact on Ameren's and Ameren Missouri's results of operations, financial position, and liquidity. To the extent investments in environmental control technology are reflected and recovered on a timely basis in rate base, Ameren's and Ameren Missouri's earnings may benefit from increased investment in such control technology.
NSR and Clean Air Litigation
In January 2011, the Department of Justice on behalf of the EPA filed a complaint against Ameren Missouri in the United States District Court for the Eastern District of Missouri. The EPA's complaint, as amended in October 2013, alleges that in performing projects at its Rush Island coal-fired energy center in 2007 and 2010, Ameren Missouri violated provisions of the Clean Air Act and Missouri law. In January 2012, the United States District Court granted, in part, Ameren Missouri's motion to dismiss various aspects of the EPA's penalty claims. The EPA's claims for unspecified injunctive relief remain. The trial in this matter is currently scheduled to begin in January 2015. Ameren Missouri believes its defenses are meritorious and will defend itself vigorously. However, there can be no assurances that it will be successful in its efforts.
Ultimate resolution of these matters could have a material adverse impact on the future results of operations, financial position, and liquidity of Ameren and Ameren Missouri. A resolution could result in increased capital expenditures for the installation of pollution control equipment, increased operations and maintenance expenses, and penalties. We are unable to predict the ultimate resolution of these matters or the costs that might be incurred.
Clean Water Act
In March 2011, the EPA announced a proposed rule applicable to cooling water intake structures at existing power plants. The proposed rule would impose standards for reducing the mortality of aquatic organisms impinged on the plant's intake screens or entrained through the plant's cooling water system. All coal-fired, nuclear, and combined cycle energy centers at Ameren Missouri with cooling water systems are subject to this proposed rule. The EPA has agreed to finalize the rule in April 2014. When finalized the final rule could have an adverse effect on our results of operations, financial position, and liquidity if its implementation requires the installation of cooling towers or extensive modifications to the cooling water systems at our energy centers.
In April 2013, the EPA announced its proposal to revise the effluent limitation guidelines applicable to steam electric generating units under the Clean Water Act. Effluent limitation guidelines are national standards for wastewater discharges to surface water that are based on the effectiveness of available control technology. The EPA's proposed rule raised several compliance options that would prohibit effluent discharges of certain, but not all, waste streams and impose more stringent limitations on certain components in wastewater discharges from power plants. If the rule is enacted as proposed, Ameren Missouri would be subject to the revised limitations beginning as early as July 1, 2017, but no later than July 1, 2022. Ameren is reviewing the proposed rule and evaluating its potential impact on operations. The EPA expects to issue final guidelines in April 2014.
Ash Management
In May 2010, the EPA announced proposed new regulations regarding the management and disposal of CCR, which could affect future disposal and handling costs at our energy centers. Those proposed regulations include two options for managing CCRs, under either solid or hazardous waste regulations, but either alternative would allow for some continued beneficial uses, such as recycling of CCR without classifying it as waste. The EPA announced that its April 2013 proposed revisions to the effluent limitations applicable to steam electric generating units would apply to ash ponds and CCR management and that it intended to align this proposal with the CCR rules when finalized. The EPA is expected to issue a final rule in December 2014. Ameren Missouri is currently evaluating all of the proposed regulations to determine whether current management of CCR, including beneficial reuse, and the use of the ash ponds should be altered. Ameren Missouri is evaluating the potential costs associated with compliance with the proposed regulation of CCR impoundments and landfills, which could be material, if such regulations are adopted.
Remediation
We are involved in a number of remediation actions to clean up sites impacted by hazardous substances as required by federal and state law. Such statutes require that responsible parties fund remediation actions regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site. Ameren Missouri and Ameren Illinois have each been identified by the federal or state governments as a potentially responsible party (PRP) at several contaminated sites.
As of December 31, 2013, Ameren Illinois owned or was otherwise responsible for 44 former MGP sites in Illinois. These sites are in various stages of investigation, evaluation, remediation, and closure. Based on current estimated plans, Ameren Illinois could substantially conclude remediation efforts at most of these sites by 2018. The ICC permits Ameren Illinois to recover remediation and litigation costs associated with its former MGP sites from its electric and natural gas utility customers through environmental adjustment rate riders. To be recoverable, such costs must be prudently incurred. Costs are subject to annual review by the ICC.
As of December 31, 2013, Ameren Missouri has one remaining former MGP site for which remediation is scheduled. Remediation is complete at the other Ameren Missouri former MGP sites. Ameren Missouri does not currently have a rate rider mechanism that permits it to recover from utility customers remediation costs associated with MGP sites.
The following table presents, as of December 31, 2013, the estimated obligation to complete the remediation of these former MGP sites.
	Estimate						Recorded
	Low			High			Liability(a)
Ameren	$	278		$	338		$	278
Ameren Missouri	4			5			4
Ameren Illinois	274			333			274
(a)	Recorded liability represents the estimated minimum probable obligations, as no other amount within the range provided a better estimate.
The scope and extent to which these former MGP sites are remediated may increase as remediation efforts continue. Considerable uncertainty remains in these estimates, as many factors can influence the ultimate actual costs, including site specific unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances and site accessibility. The actual costs may vary substantially from these estimates.
Ameren Illinois used an off-site landfill, which Ameren Illinois did not own, in connection with the former operation of an energy center. Ameren Illinois could be required to perform certain maintenance activities associated with that landfill. As of December 31, 2013, Ameren Illinois estimated the obligation related to this site at $0.5 million to $6 million. Ameren Illinois recorded a liability of $0.5 million to represent its estimated minimum obligation for this site, as no other amount within the range was a better estimate. Ameren Illinois is also responsible for the cleanup of some underground storage tanks and a water treatment plant in Illinois. As of December 31, 2013, Ameren Illinois recorded a liability of $0.8 million to represent its estimate of the obligation for these sites.
Ameren Missouri is investigating and addressing two waste sites in Missouri as a result of federal agency mandates. One of the cleanup sites is a former coal tar distillery located in St. Louis, Missouri. In 2008, the EPA issued an administrative order to Ameren Missouri pertaining to this distillery operated by Koppers Company or its predecessor and successor companies. While Ameren Missouri is the current owner of the site, it did not conduct any of the manufacturing operations involving coal tar or its byproducts. Ameren Missouri, along with two other PRPs, is currently performing a site investigation. As of December 31, 2013, Ameren Missouri estimated its obligation at $2 million to $5 million. Ameren Missouri recorded a liability of $2 million to represent its estimated minimum obligation, as no other amount within the range was a better estimate. Ameren Missouri's other active federal agency-mandated cleanup site in Missouri is in Cape Girardeau. Ameren Missouri was a customer of an electrical equipment repair and disposal company that previously operated a facility at this site. A trust was established in the early 1990s by several businesses and governmental agencies to fund the investigation and cleanup of this site, which was completed in 2005. Ameren Missouri anticipates that this trust fund will be sufficient to complete the remaining adjacent off-site cleanup, and therefore, Ameren Missouri believes it has no liability at December 31, 2013, for this site.
Ameren Missouri also has a federal agency mandate to complete an investigation for a site in Illinois. In 2000, the EPA notified Ameren Missouri and numerous other companies, including Solutia, that former landfills and lagoons in Sauget, Illinois, may contain soil and groundwater contamination. These sites are known as Sauget Area 2. From about 1926 until 1976, Ameren Missouri operated an energy center adjacent to Sauget Area 2. Ameren Missouri currently owns a parcel of property that was once used as a landfill. Under the terms of an Administrative Order on Consent, Ameren Missouri joined with other potentially responsible parties to evaluate the extent of potential contamination with respect to Sauget Area 2.
The Sauget Area 2 investigations overseen by the EPA have been completed. In December 2013, the EPA issued its record of decision approving the investigation and the remediation alternatives recommended by the potentially responsible parties. Further negotiation among the potentially responsible parties will determine how to fund the implementation of the EPA approved cleanup remedies. As of December 31, 2013, Ameren Missouri estimated its obligation related to Sauget Area 2 at $0.3 million to $10 million. Ameren Missouri recorded a liability of $0.3 million to represent its estimated minimum obligation, as no other amount within the range was a better estimate.
In December 2012, Ameren Missouri signed an administrative order with the EPA and agreed to investigate soil and groundwater conditions at an Ameren Missouri owned substation in St. Charles, Missouri. As of December 31, 2013, Ameren Missouri estimated the obligation related to the cleanup at $1.6 million to $4.5 million. Ameren Missouri recorded a liability of $1.6 million to represent its estimated minimum obligation for this site, as no other amount within the range was a better estimate.
Our operations or those of our predecessor companies involve the use of, disposal of, and in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such practices will result in future environmental commitments or will affect our results of operations, financial position, or liquidity.
Pumped-storage Hydroelectric Facility Breach
In December 2005, there was a breach of the upper reservoir at Ameren Missouri's Taum Sauk pumped-storage hydroelectric energy center. This resulted in significant flooding in the local area, which damaged a state park. The rebuilt Taum Sauk energy center became fully operational in April 2010.
Ameren Missouri had liability insurance coverage for the Taum Sauk incident, subject to certain limits and deductibles. As of December 31, 2013, Ameren Missouri had an insurance receivable balance of $68 million.
In June 2010, Ameren Missouri sued an insurance company that was providing Ameren Missouri with liability coverage on the date of the Taum Sauk incident. In the litigation, filed in the United States District Court for the Eastern District of Missouri, Ameren Missouri claimed that the insurance company breached its duty to indemnify Ameren Missouri for the losses resulting from the incident. In January 2011, the district court ruled that the parties must first pursue alternative dispute resolution and enforced the forum selection clause of their coverage agreement. The forum selection clause requires use of New York law and effectively requires mandatory arbitration. Ameren Missouri appealed the January 2011 ruling to the United States Court of Appeals for the Eighth Circuit. In August 2012, the court of appeals remanded the case to the district court for consideration of whether Missouri public policy voids the forum selection clause. In September 2013, the district court ruled that Missouri public policy does void the forum selection clause.
Separately, in April 2012, Ameren Missouri sued a second insurance company that was providing Ameren Missouri with liability coverage on the date of the Taum Sauk incident. In the April 2012 litigation, which is pending in the United States District Court for the Eastern District of Missouri, Ameren Missouri claimed the insurance company breached its duty to indemnify Ameren Missouri for the losses resulting from the incident. The insurance company filed a motion to compel arbitration, which the district court denied. In April 2013, the United States Court of Appeals for the Eighth Circuit affirmed the district court’s denial of the insurer’s motion and remanded the case to the district court.
Ameren's and Ameren Missouri's results of operations, financial position and liquidity could be adversely affected if Ameren Missouri's remaining liability insurance claims are not paid by insurers.
Asbestos-related Litigation
Ameren, Ameren Missouri and Ameren Illinois have been named, along with numerous other parties, in a number of lawsuits filed by plaintiffs claiming varying degrees of injury from asbestos exposure at our present or former energy centers. Most have been filed in the Circuit Court of Madison County, Illinois. The total number of defendants named in each case varies, with the average number of parties being 82 as of December 31, 2013. Each lawsuit seeks unspecified damages that, if awarded at trial, typically would be shared among the various defendants.
In connection with the divestiture of New AER to IPH, certain agreements related to former Ameren Illinois energy centers were amended to provide that Ameren Illinois will continue to retain asbestos exposure-related liabilities for claims arising or existing from activities prior to its transfer of the ownership of the former Ameren Illinois energy centers to New AER. IPH will be responsible for any asbestos-related claims arising from activities that occur after the effective date of the divestiture. No claims arose solely from activities in the period after the transfer of the energy centers from Ameren Illinois to AER, but before IPH took ownership of New AER.
The following table presents the pending asbestos-related lawsuits filed against the Ameren Companies as of December 31, 2013:
Ameren		Ameren	Ameren		Total(a)
		Missouri	Illinois
1		47	50		71
(a)	Total does not equal the sum of the subsidiary unit lawsuits because some of the lawsuits name multiple Ameren entities as defendants.
At December 31, 2013, Ameren, Ameren Missouri and Ameren Illinois had liabilities of $11 million, $5 million, and $6 million, respectively, recorded to represent their best estimate of their obligations related to asbestos claims.
Ameren Illinois has a tariff rider to recover the costs of IP asbestos-related litigation claims, subject to the following terms: 90% of cash expenditures in excess of the amount included in base electric rates are to be recovered from a trust fund that was established when Ameren acquired IP. At December 31, 2013, the trust fund balance was $23 million, including accumulated interest. If cash expenditures are less than the amount in base rates, Ameren Illinois will contribute 90% of the difference to the trust fund. Once the trust fund is depleted, 90% of allowed cash expenditures in excess of base rates will be recovered through charges assessed to customers under the tariff rider. The rider will permit recovery from customers within IP’s historical service territory.
Ameren Illinois Municipal Taxes
Ameren Illinois received tax liability notices from the city of O'Fallon, Illinois, relating to prior-period electric and natural gas municipal taxes. The city alleges that Ameren Illinois failed to collect prior-period taxes from more than 2,400 accounts, primarily in annexed areas, for the period 2004 through 2012. In July 2013, the O’Fallon city administrator issued an order stating that Ameren Illinois was liable to the city of O’Fallon for $4 million. In August 2013, Ameren Illinois filed an appeal and a stay of the O’Fallon city administrator’s order to the St. Clair County Circuit Court. In addition, in December 2012, the city of Peoria issued a tax liability notice alleging that Ameren Illinois failed to collect prior-period municipal taxes from certain accounts. In September 2013, a hearing officer issued an order stating that Ameren Illinois was liable to the city of Peoria for $0.5 million. Ameren Illinois filed an appeal and a stay of the order to the Peoria County Circuit Court. Ameren Illinois believes its defenses to the allegations are meritorious and will defend itself vigorously. As of December 31, 2013, Ameren Illinois estimated its obligation at $1 million to $5 million. Ameren Illinois recorded a liability of $1 million to represent its estimated minimum obligation to the city of O'Fallon and the city of Peoria, as no other amount within the range was a better estimate.
In addition, at the end of 2012, five other cities issued tax liability notices alleging that Ameren Illinois failed to collect prior-period taxes from certain accounts. At this time, it is premature in Ameren Illinois' review of the additional notices received at the end of 2012 to reasonably estimate any likelihood of loss.

Divestiture_Transactions_and_D

Divestiture Transactions and Discontinued Operations (Notes)	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
DIVESTITURE TRANSACTIONS AND DISCONTINUED OPERATIONS	'
	NOTE 16 – DIVESTITURE TRANSACTIONS AND DISCONTINUED OPERATIONS
	Transaction Agreement with IPH
	On December 2, 2013, Ameren completed the divestiture of New AER to IPH, in accordance with the transaction agreement between Ameren and IPH dated March 14, 2013, as amended by a letter agreement entered into by Ameren and IPH on December 2, 2013. IPH acquired all of the outstanding limited liability interests in New AER, which was a newly created, wholly owned subsidiary of AER. Prior to the closing, AER effected a reorganization that, among other things, transferred substantially all of its assets and liabilities to New AER, other than (i) any outstanding debt obligations of AER to Ameren or its other subsidiaries, except for certain intercompany balances discussed below; (ii) the assets and liabilities associated with Genco’s Meredosia and Hutsonville energy centers; (iii) the obligations relating to Ameren's single-employer pension and postretirement benefit plans; and (iv) the deferred income tax assets and liabilities associated with Ameren's ownership of these retained assets and liabilities.
	Ameren retained certain pension and postretirement benefit obligations associated with current and former employees of AER, with the exception of the pension and postretirement benefit obligations associated with current and former employees of EEI, which were assumed by IPH. Ameren retained the Meredosia and Hutsonville energy centers, including their AROs, which totaled $31 million as of December 31, 2013. These energy centers were abandoned and had an immaterial property and plant asset balance as of December 31, 2013. All other AROs associated with AER were assumed by New AER or by Rockland Capital, the third-party buyer of the Grand Tower energy center, as discussed below.
	Upon the IPH transaction agreement closing, all intercompany agreements and debt that existed between New AER and its subsidiaries, on the one hand, and Ameren and its non-New AER affiliates, on the other hand, with the exception of certain agreements, such as supply obligations to Ameren Illinois, a note from Marketing Company to Ameren relating to cash collateral that remained outstanding at closing, Genco money pool advances and certain New AER subsidiary money pool borrowings, were either retained or cancelled by Ameren, without any cost or obligation to IPH or New AER and its subsidiaries. Immediately prior to the closing of the divestiture, the money pool borrowings through which Ameren provided cash collateral to Marketing Company were converted to a note payable to Ameren, which is payable, with interest, 24 months after closing or sooner as cash collateral requirements are reduced. The balance of the note was $18 million at December 31, 2013, and is reflected on Ameren's consolidated balance sheet in "Other assets."
	Pursuant to the transaction agreement, as amended by the December 2, 2013 letter agreement, Ameren caused $235 million of cash to be retained at New AER immediately prior to closing, which included amounts previously paid to Genco for the sale of the Elgin, Gibson City, and Grand Tower energy centers to Medina Valley as well as additional amounts retained at Genco, AERG, and Marketing Company. Within 120 days after the closing of the divestiture, a working capital adjustment will be finalized, which may result in a cash payment from Ameren to IPH or from IPH to Ameren. Ameren received no cash proceeds as a result of the divestiture of New AER. Pursuant to the transaction agreement, as amended, Ameren is obligated to pay up to $39 million for certain contingent liabilities. Of these liabilities, $29 million are included in "Other deferred credits and liabilities" and $10 million are included in "Accounts and wages payable" on Ameren's December 31, 2013 consolidated balance sheet.
	As a condition to the transaction agreement, Genco exercised the amended put option agreement for the sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers to Medina Valley. In October 2013, Genco completed the sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers to Medina Valley, receiving total payments of $137.5 million. The third-party sale of these energy centers to Rockland Capital was completed on January 31, 2014 and is discussed below.
	Sale of Gas-fired Energy Centers
	Prior to entry into the transaction agreement with IPH, Genco entered into a put option agreement, as amended, with Medina Valley. This agreement gave Genco the option to sell to Medina Valley the Elgin, Gibson City, and Grand Tower gas-fired energy centers for the fair market value of the energy centers, as determined by three independent appraisers. Genco exercised its option, and in October 2013 completed its sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers to Medina Valley for $137.5 million, which was the fair value of the gas-fired energy centers as determined by the three independent appraisers.
	The transaction agreement with IPH, as amended, provides that if the Elgin, Gibson City, and Grand Tower gas-fired energy centers are subsequently sold by Medina Valley and if Medina Valley receives additional proceeds from such sale, Medina Valley will pay Genco any proceeds from such sale, net of taxes and other expenses, in excess of the $137.5 million previously paid to Genco.
	On January 31, 2014, Medina Valley completed the sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers to Rockland Capital for a total purchase price of $168 million, before consideration of a net working capital adjustment. The agreement with Rockland Capital required $17 million of the purchase price to be held in escrow until the two-year anniversary of the closing of the sale to fund certain indemnity obligations, if any, of Medina Valley. The net working capital adjustment will be finalized within 120 days after the January 31, 2014 closing date. As a result, pending final resolution of the net working capital adjustment, taxes, and other expenses, Medina Valley expects to pay Genco any remaining portion of the escrow balance on January 31, 2016. Ameren will not record a gain from its sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers.
	Discontinued Operations Presentation
	As of March 14, 2013, Ameren determined that New AER and the Elgin, Gibson City, and Grand Tower gas-fired energy centers qualified for discontinued operations presentation. In addition, effective December 2, 2013, coinciding with the completion of the divestiture of New AER to IPH, Ameren determined that the Meredosia and Hutsonville energy centers had been abandoned. Ameren is prohibited from operating these energy centers through December 31, 2020, as a provision of the Illinois Pollution Control Board's November 2013 order granting IPH a variance of the MPS. As a result, Ameren determined the Meredosia and Hutsonville energy centers qualified for discontinued operations presentation as of December 2, 2013.
	New AER and the Elgin, Gibson City, Grand Tower, Meredosia, and Hutsonville energy centers have been classified collectively in Ameren’s consolidated financial statements as discontinued operations for all periods presented in this report. The disposal groups have been aggregated in the disclosures below. The following table presents the components of discontinued operations in Ameren's consolidated statement of income (loss) for the years ended December 31, 2013, 2012 and 2011:
		Year ended
		2013				2012				2011
	Operating revenues	$	1,037			$	1,047			$	1,358
	Operating expenses	(1,207		)	(a)	(3,474		)	(b)	(1,150		)
	Operating income (loss)	(170		)		(2,427		)		208
	Other income (loss)	(1		)		—				1
	Interest charges	(39		)		(56		)		(64		)
	Income (loss) before income taxes	(210		)		(2,483		)		145
	Income tax (expense) benefit	(13		)		987				(56		)
	Income (loss) from discontinued operations, net of taxes	$	(223	)		$	(1,496	)		$	89
	(a)	Includes a $201 million pretax loss on disposal relating to the New AER divestiture.
	(b)	Includes a noncash pretax asset impairment charge of $628 million to reduce the carrying value of AERG’s Duck Creek energy center to its estimated fair value under held and used accounting guidance. In addition, includes a noncash pretax asset impairment charge of $1.95 billion to reduce the carrying values of all the AER coal and natural gas-fired energy centers, except the Joppa coal-fired energy center, to their estimated fair values, under held and used accounting guidance, as a result of the decision in December 2012 that Ameren intended to exit the Merchant Generation business.
	Upon completion of the divestiture of New AER, Ameren finalized its loss on disposal. Ameren received no cash proceeds from IPH for the divestiture of New AER. Ameren recorded a pretax charge to earnings related to the New AER divestiture of $201 million for the year ended December 31, 2013. The loss was recorded in “Operating expenses” within the components of the discontinued operations statement of income (loss). The ultimate loss on disposal may differ as a result of the finalization of the working capital adjustment within 120 days of close.
	In 2013, Ameren adjusted the accumulated deferred income taxes on its consolidated balance sheet to reflect the excess of tax basis over financial reporting basis of its stock investment in AER. This change in basis resulted in a discontinued operations deferred tax expense of $99 million, which was partially offset by the expected tax benefits of $86 million related to the pretax loss from discontinued operations including the loss on disposal, during the year ended December 31, 2013. The final tax basis of the AER disposal group and the related tax benefit resulting from the transaction agreement with IPH are dependent upon the resolution of tax matters under IRS audit, including the adoption of recently issued guidance from the IRS related to tangible property repairs and other matters. As a result, tax expense and benefits ultimately realized in discontinued operations may differ materially from those recorded as of December 31, 2013.
	As the Elgin, Gibson City, and Grand Tower gas-fired energy center disposal group continued to meet the discontinued operations criteria at December 31, 2013, Ameren evaluated whether any impairment existed by comparing the disposal group’s carrying value to the estimated fair value of the disposal group, less cost to sell. In December 2012, Ameren recorded a noncash long-lived asset impairment charge to reduce the carrying value of AER’s energy centers, including the Elgin, Gibson City, and Grand Tower gas-fired energy centers, to their estimated fair values under the accounting guidance for held and used assets. Ameren did not record any additional impairment relating to the Elgin, Gibson City, and Grand Tower energy centers for the year ended December 31, 2013. As discussed above, on January 31, 2014, Medina Valley completed the sale of the Elgin, Gibson City, and Grand Tower gas-fired energy centers to Rockland Capital for a total purchase price of $168 million, before consideration of a net working capital adjustment. Ameren will not recognize a gain from the third party sale to Rockland Capital for any value in excess of its $137.5 million carrying value for this disposal group since any excess amount that Medina Valley may receive, net of taxes and other expenses, over the carrying value, will ultimately be paid to Genco pursuant to the transaction agreement with IPH.
	Long-lived Asset Impairments
	New AER and the Elgin, Gibson City, and Grand Tower energy centers were impaired under held and used accounting guidance in 2012 and the Meredosia and Hutsonville energy centers were impaired under held and used accounting guidance in 2011. The 2012 and 2011 impairments are discussed below.
	As a result of the December 2012 decision that Ameren intended to, and it was probable that it would, exit the Merchant Generation segment before the end of the Merchant Generation long-lived assets' previously estimated useful lives, Ameren determined that estimated undiscounted cash flows during the period in which it expected to continue to own certain energy centers would be insufficient to recover the carrying value of those energy centers. Accordingly, Ameren recorded a noncash pretax impairment charge of $1.95 billion in the fourth quarter of 2012 to reduce the carrying values of all of the Merchant Generation's coal and natural gas-fired energy centers, except the Joppa coal-fired energy center, to their estimated fair values. The estimated undiscounted cash flows of the Joppa coal-fired energy center exceeded its carrying value; therefore, the Joppa coal-fired energy center was unimpaired.
	In early 2012, the observable market price for power for delivery in that year and in future years in the Midwest sharply declined below 2011 levels, primarily because of declining natural gas prices and the impact of the stay of the CSAPR. As a result of this sharp decline in the market price of power and the related impact on electric margins, Genco decelerated the construction of two scrubbers at its Newton energy center in February 2012. The sharp decline in the market price of power in early 2012 and the related impact on electric margins, as well as the deceleration of construction of Genco's Newton energy center scrubber project, caused Ameren to evaluate, during the first quarter of 2012, whether the carrying values of Merchant Generation coal-fired energy centers were recoverable. AERG's Duck Creek energy center's carrying value exceeded its estimated undiscounted future cash flows. As a result, Ameren recorded a noncash pretax asset impairment charge of $628 million to reduce the carrying value of that energy center to its estimated fair value during the first quarter of 2012.
	In December 2011, Genco ceased operations at its Meredosia and Hutsonville energy centers. As a result, Ameren recorded a noncash pretax asset impairment charge of $26 million to reduce the carrying value of the Meredosia and Hutsonville energy centers to their estimated fair values and a $4 million impairment for materials and supplies.
	Key assumptions used in the determination of estimated undiscounted cash flows for the 2012 and 2011 long-lived assets tested for impairment under held and used accounting guidance discussed above included forward price projections for energy and fuel costs, the expected life or duration of ownership of the long-lived assets, environmental compliance costs and strategies, and operating costs. Those same cash flow assumptions, along with a discount rate and terminal year earnings multiples, were used to estimate the fair value of each energy center. These assumptions are subject to a high degree of judgment and complexity. The fair value estimate of these long-lived assets was based on a combination of the income approach, which considers discounted cash flows, and the market approach, which considers market multiples for similar assets within the electric generation industry. The fair value estimate was determined using observable inputs and significant unobservable inputs, which are Level 3 inputs as defined by accounting guidance for fair value measurements.
	The following table presents the carrying amounts of the components of assets and liabilities segregated on Ameren's consolidated balance sheets as discontinued operations at December 31, 2013, and 2012:
		31-Dec-13				31-Dec-12
	Assets of discontinued operations
	Cash and cash equivalents	$	—			$	25
	Accounts receivable and unbilled revenue	5				102
	Materials and supplies	5				135
	Mark-to-market derivative assets	—				102
	Property and plant, net	142				748
	Accumulated deferred income taxes, net(a)	13				395
	Other assets	—				104
	Total assets of discontinued operations	$	165			$	1,611
	Liabilities of discontinued operations
	Accounts payable and other current obligations	$	5			$	141
	Mark-to-market derivative liabilities	—				63
	Long-term debt, net	—				824
	Asset retirement obligations(b)	40				97
	Pension and other postretirement benefits	—				40
	Other liabilities	—				28
	Total liabilities of discontinued operations	$	45			$	1,193
	Accumulated other comprehensive income (c)	$	—			$	19
	Noncontrolling interest(d)	$	—			$	8
	(a)	The December 31, 2013 balance primarily consists of deferred income tax assets related to the abandoned Meredosia and Hutsonville energy centers.
	(b)	Includes AROs associated with the abandoned Meredosia and Hutsonville energy centers of $31 million and $26 million at December 31, 2013, and 2012, respectively.
	(c)	Accumulated other comprehensive income related to discontinued operations included in “Accumulated other comprehensive loss” on Ameren’s December 31, 2012, consolidated balance sheet. This balance related to New AER assets and liabilities that were realized or removed from Ameren’s consolidated balance sheet either before or at the December 2, 2013 closing of the New AER divestiture.
	(d)	The 20% ownership interest of EEI not owned by Ameren was included in “Noncontrolling interests” on Ameren’s December 31, 2012, consolidated balance sheet. This noncontrolling interest was removed from Ameren’s consolidated balance sheet at the December 2, 2013 closing of the New AER divestiture.
	Ameren has continuing transactions with New AER. Ameren Illinois has power supply agreements with Marketing Company, which are a result of the power procurement process in Illinois administered by the IPA, as required by the Illinois Public Utilities Act. Ameren Illinois continues to purchase power and to purchase trade receivables as required by Illinois law. Ameren Illinois and ATXI continue to sell transmission services to Marketing Company. Also, the transaction agreement requires Ameren (parent) to maintain certain guarantees discussed below. Immediately prior to the transaction agreement closing, the money pool borrowings through which Ameren provided cash collateral to Marketing Company were converted to a note payable to Ameren, which is payable, with interest, 24 months after closing or sooner as cash collateral requirements are reduced. Also, within 120 days after closing, a working capital adjustment will be finalized, which may result in a cash payment from Ameren to New AER or from New AER to Ameren. Ameren has determined that the continuing cash flows generated by these arrangements are not significant and, accordingly, are not deemed to be direct cash flows of the divested business. Additionally, these arrangements do not provide Ameren with the ability to significantly influence the operating results of New AER. Ameren will not have significant continuing involvement with or material cash flows from the Elgin, Gibson City, or Grand Tower energy centers after their sale.
	Ameren Guarantees
	Upon the divestiture of New AER, the transaction agreement between Ameren and IPH requires Ameren (parent) to maintain its financial obligations with respect to all credit support provided to New AER as of the closing date of such divestiture. Ameren must also provide such additional credit support as required by contracts entered into prior to the closing date, in each case for up to 24 months after the closing. IPH shall indemnify Ameren for any payments Ameren makes pursuant to these credit support obligations if the counterparty does not return the posted collateral to Ameren. IPH's indemnification obligation is secured by certain AERG and Genco assets. In addition, Dynegy has provided a limited guarantee of $25 million to Ameren (parent) pursuant to which Dynegy will, among other things, guarantee IPH's indemnification obligations for a period of up to 24 months after the closing.
At December 31, 2013, Ameren had a total of $190 million in guarantees outstanding, which included:
•	$176 million related to guarantees supporting Marketing Company for physically and financially settled power transactions with its counterparties that were in place at the December 2, 2013 closing of the divestiture, as well as for Marketing Company's clearing broker and other service agreements. If Marketing Company did not fulfill its obligations to these counterparties who had active open positions as of December 31, 2013, Ameren would have been required under its guarantees to provide $6 million to the counterparties.
•	$14 million related to requirements for leasing agreements and potential environmental obligations.
Additionally, at December 31, 2013, Ameren had issued letters of credit totaling $11 million as credit support on behalf of New AER.
Ameren has not recorded a reserve for these contingent obligations because it does not believe a payment for any of these guarantees is probable as of December 31, 2013.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2013
Segment Reporting Information, Profit (Loss) [Abstract]	'
SEGMENT INFORMATION	'
	SEGMENT INFORMATION
	Ameren has two reportable segments: Ameren Missouri and Ameren Illinois. The Ameren Missouri segment for both Ameren and Ameren Missouri includes all the operations of Ameren Missouri’s business as described in Note 1 – Summary of Significant Accounting Policies. The Ameren Illinois segment for both Ameren and Ameren Illinois consists of all of the operations of Ameren Illinois as described in Note 1 – Summary of Significant Accounting Policies. The category called Other primarily includes Ameren parent company activities, Ameren Services, and ATXI. The Other category also includes certain corporate activities previously included in the Merchant Generation segment. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information.
	The following table presents information about the reported revenues and specified items reflected in Ameren’s net income attributable to Ameren Corporation from continuing operations for the years ended December 31, 2013, 2012, and 2011, and total assets in continuing operations as of December 31, 2013, 2012, and 2011.
	Ameren
		Ameren		Ameren		Other				Intersegment			Consolidated
		Missouri		Illinois						Eliminations
	2013
	External revenues	$	3,516	$	2,307	$	15			$	—		$	5,838
	Intersegment revenues	25		4		2				(31		)	—
	Depreciation and amortization	454		243		9				—			706
	Interest and dividend income	27		2		1				—			30
	Interest charges	210		143		45				—			398
	Income taxes (benefit)	242		110		(41		)		—			311
	Net income (loss) attributable to Ameren Corporation from continuing operations	395		160		(43		)		—			512
	Capital expenditures	648		701		30			(a)	—			1,379
	Total assets	12,904		7,454		752				(233		)	20,877		(b)
	2012
	External revenues	$	3,252	$	2,524	$	5			$	—		$	5,781
	Intersegment revenues	20		1		3				(24		)	—
	Depreciation and amortization	440		221		12				—			673
	Interest and dividend income	32		—		—				—			32
	Interest charges	223		129		40				—			392
	Income taxes (benefit)	252		94		(39		)		—			307
	Net income (loss) attributable to Ameren Corporation from continuing operations	416		141		(41		)		—			516
	Capital expenditures	595		442		26			(a)	—			1,063
	Total assets	13,043		7,282		1,228				(934		)	20,619		(b)
	2011
	External revenues	$	3,360	$	2,784	$	4			$	—		$	6,148
	Intersegment revenues	23		3		3				(29		)	—
	Depreciation and amortization	408		215		20				—			643
	Interest and dividend income	30		1		—				—			31
	Interest charges	209		136		42				—			387
	Income taxes (benefit)	161		127		(34		)		—			254
	Net income (loss) attributable to Ameren Corporation from continuing operations	287		193		(49		)		—			431
	Capital expenditures	550		351		(20		)	(a)	—			881
	Total assets	12,757		7,213		1,211				(1,179		)	20,002		(b)
	.
	(a)	Includes the elimination of intercompany transfers.
	(b)	Excludes total assets from discontinued operations of $165 million, $1,611 million, and $3,721 million as of December 31, 2013, 2012, and 2011, respectively.

Selected_Quarterly_Information

Selected Quarterly Information	12 Months Ended
	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]	'
SELECTED QUARTERLY INFORMATION	'
	SELECTED QUARTERLY INFORMATION (Unaudited) (In millions, except per share amounts)
	Ameren	2013												2012
	Quarter ended (a)	31-Mar			30-Jun			30-Sep			31-Dec			31-Mar			30-Jun		30-Sep		31-Dec
	Operating revenues	$	1,475		$	1,403		$	1,638		$	1,322		$	1,412		$	1,402	$	1,709	$	1,258
	Operating income	185			261			567			171			159			347		570		112
	Net income (loss)(b)	(143		)	96			304			38			(403		)	210		374		(1,155		)
	Net income attributable to Ameren Corporation – continuing operations	$	54		$	105		$	305		$	48		$	38		$	164	$	302	$	12
	Net income (loss) attributable to Ameren Corporation – discontinued operations (b)	(199		)	(10		)	(3		)	(11		)	(441		)	47		72		(1,168		)
	Net income (loss) attributable to Ameren Corporation	$	(145	)	$	95		$	302		$	37		$	(403	)	$	211	$	374	$	(1,156	)
	Earnings per common share – basic – continuing operations	$	0.22		$	0.44		$	1.26		$	0.19		$	0.16		$	0.67	$	1.25	$	0.05
	Earnings (loss) per common share – basic – discontinued operations	(0.82		)	(0.05		)	(0.01		)	(0.04		)	(1.82		)	0.2		0.29		(4.81		)
	Earnings (loss) per common share – basic	$	(0.60	)	$	0.39		$	1.25		$	0.15		$	(1.66	)	$	0.87	$	1.54	$	(4.76	)
	Earnings per common share – diluted – continuing operations	$	0.22		$	0.44		$	1.25		$	0.19		$	0.16		$	0.67	$	1.25	$	0.05
	Earnings (loss) per common share – diluted – discontinued operations	(0.82		)	(0.05		)	(0.01		)	(0.04		)	(1.82		)	0.2		0.29		(4.81		)
	Earnings (loss) per common share – diluted	$	(0.60	)	$	0.39		$	1.24		$	0.15		$	(1.66	)	$	0.87	$	1.54	$	(4.76	)
	(a)	The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is due to the effects of rounding and to changes in the number of weighted-average shares outstanding each period.
	(b)	Includes pretax asset impairment charge of $2.6 billion recorded in discontinued operations during the year ended December 31, 2012. See Note 16 – Divestiture Transactions and Discontinued Operations under Part II, Item 8, for additional information.
	Ameren Missouri Quarter ended		Operating			Operating			Net income			Net income (loss)
			revenues			income			(loss)			available
												to common
												stockholder
	March 31, 2013		$	796		$	111		$	41		$	40
	March 31, 2012		691			78			22			21
	June 30, 2013		889			179			85			84
	June 30, 2012		844			269			144			143
	September 30, 2013		1,093			417			239			238
	September 30, 2012		1,064			429			237			236
	December 31, 2013		763			96			33			33
	December 31, 2012		673			69			16			16
	Ameren Illinois Quarter ended		Operating			Operating			Net income			Net income
			revenues			income						available
												to common
												stockholder
	March 31, 2013		$	684		$	85		$	32		$	31
	March 31, 2012		724			89			28			27
	June 30, 2013		516			87			32			31
	June 30, 2012		564			86			33			32
	September 30, 2013		547			158			77			77
	September 30, 2012		648			151			71			71
	December 31, 2013		564			85			22			21
	December 31, 2012		589			51			12			11

Schedule_I_Condensed_Financial

Schedule I - Condensed Financial Information Of Parent	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
Condensed Financial Information Of Parent	'
	SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT
	AMEREN CORPORATION
	CONDENSED STATEMENT OF INCOME (LOSS) AND COMPREHENSIVE INCOME (LOSS)
	For the Years Ended December 31, 2013, 2012 and 2011
	(In millions)	2013			2012			2011
	Operating revenues	$	—		$	—		$	—
	Operating expenses	26			17			13
	Operating loss	(26		)	(17		)	(13		)
	Equity in earnings of subsidiaries	546			546			464
	Interest income from affiliates	3			3			5
	Miscellaneous expense	5			4			4
	Interest charges	42			39			41
	Income tax (benefit)	(36		)	(27		)	(20		)
	Net Income Attributable to Ameren Corporation – Continuing Operations	512			516			431
	Net Income (Loss) Attributable to Ameren Corporation – Discontinued Operations	(223		)	(1,490		)	88
	Net Income (Loss) Attributable to Ameren Corporation	$	289		$	(974	)	$	519
	Net Income Attributable to Ameren Corporation – Continuing Operations	$	512		$	516		$	431
	Other Comprehensive Income (Loss), Net of Taxes:
	Pension and other postretirement benefit plan activity, net of income taxes (benefit) of $16, $(6), and $(14), respectively	30			(8		)	(19		)
	Comprehensive Income from Continuing Operations Attributable to Ameren Corporation	542			508			412
	Net Income (Loss) Attributable to Ameren Corporation – Discontinued Operations	(223		)	(1,490		)	88
	Other Comprehensive Income (Loss) from Discontinued Operations, Net of Income Taxes	(19		)	50			(14		)
	Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Corporation	(242		)	(1,440		)	74
	Comprehensive Income (Loss) Attributable to Ameren Corporation	$	300		$	(932	)	$	486
	SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT
	AMEREN CORPORATION
	CONDENSED BALANCE SHEET
	(In millions)	31-Dec-13			31-Dec-12
	Assets:
	Cash and cash equivalents	$	11		$	23
	Advances to money pool	334			316
	Accounts and notes receivable – affiliates	27			31
	Miscellaneous accounts and notes receivable	125			—
	Other current assets	42			49
	Total current assets	539			419
	Investments in subsidiaries – continuing operations	6,336			6,315
	Investments in subsidiaries – discontinued operations	(5		)	(353		)
	Note receivable - affiliates	51			462
	Accumulated deferred income taxes, net	623			210
	Other non-current assets	141			110
	Total assets	$	7,685		$	7,163
	Liabilities and Stockholders’ Equity:
	Current maturities of long-term debt	$	425		$	—
	Short-term debt	368			—
	Accounts payable	119			3
	Accounts payable – affiliates	4			10
	Other current liabilities	20			30
	Total current liabilities	936			43
	Long-term debt	—			424
	Other deferred credits and liabilities	205			80
	Total liabilities	1,141			547
	Commitments and Contingencies
	Stockholders’ Equity:
	Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 242.6	2			2
	Other paid-in capital, principally premium on common stock	5,632			5,616
	Retained earnings	907			1,006
	Accumulated other comprehensive income (loss)	3			(8		)
	Total stockholders’ equity	6,544			6,616
	Total liabilities and stockholders’ equity	$	7,685		$	7,163
	SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT
	AMEREN CORPORATION
	CONDENSED STATEMENT OF CASH FLOWS
	For the Years Ended December 31, 2013, 2012 and 2011
(In millions)	2013			2012			2011
Net cash flows provided by operating activities	$	453		$	532		$	804
Cash flows from investing activities:
Money pool advances, net	(371		)	24			(276		)
Notes receivable – affiliates, net	(23		)	(20		)	358
Investments in subsidiaries	(50		)	(2		)	(94		)
Distributions from subsidiaries	1			21			3
Other	(2		)	(5		)	(5		)
Net cash flows provided by (used in) investing activities	(445		)	18			(14		)
Cash flows from financing activities:
Dividends on common stock	(388		)	(382		)	(375		)
Short-term debt and credit facility borrowings, net	368			(148		)	(481		)
Issuances of common stock	—			—			65
Net cash flows used in financing activities	(20		)	(530		)	(791		)
Net change in cash and cash equivalents	$	(12	)	$	20		$	(1	)
Cash and cash equivalents at beginning of year	23			3			4
Cash and cash equivalents at the end of year	$	11		$	23		$	3
Cash dividends received from consolidated subsidiaries	$	570		$	610		$	730
Noncash investing activity – divestiture	$	494		$	—		$	—
Noncash financing activity – dividends on common stock	—			(7		)	—
BASIS OF PRESENTATION
Ameren Corporation (parent company only) is a public utility holding company that conducts substantially all of its business operations through its subsidiaries. In accordance with authoritative accounting guidance, Ameren Corporation (parent company only) has accounted for wholly owned subsidiaries using the equity method. These financial statements are presented on a condensed basis. Additional disclosures relating to the parent company financial statements are included within the combined notes under Part II, Item 8, of this report.
SHORT-TERM DEBT AND LIQUIDITY
See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of this report for a description and details of short-term debt and liquidity needs of Ameren Corporation (parent company only).
LONG-TERM OBLIGATIONS
See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of this report for a description and details of long-term obligations of Ameren Corporation (parent company only).
COMMITMENTS AND CONTINGENCIES
See Note 15 – Commitments and Contingencies and Note 16 – Divestiture Transactions and Discontinued Operations under Part II, Item 8, of this report for a description of all material contingencies and guarantees outstanding of Ameren Corporation (parent company only).
In December 2012, Ameren determined that it intended to, and it was probable that it would, exit its Merchant Generation business before the end of the previously estimated useful lives of that business's long-lived assets. As a result of the 2012 determination, Ameren Corporation (parent company only) recorded a pretax impairment charge of $1.88 billion to reduce its investment in certain of the Merchant Generation segment's coal and natural gas-fired energy centers to their estimated fair values. On December 2, 2013, Ameren completed a divestiture that included a significant portion of that business. As a result of the divestiture in 2013, Ameren Corporation (parent company only) recorded a pretax loss on disposal of $201 million. These charges were included within "Net Income (Loss) Attributable to Ameren Corporation - Discontinued Operations" in the Ameren Corporation (parent company only) Condensed Statement of Income (Loss) and Comprehensive Income (Loss) for the years ended December 31, 2013, and 2012.
The "Miscellaneous accounts and notes receivable" on the December 31, 2013 Ameren Corporation (parent company only) Condensed Balance Sheet included a receivable from Dynegy related to the non-state-regulated subsidiary money pool borrowing balance as of the divestiture date of certain New AER subsidiaries. Additionally, a payable to Dynegy of the estimated working capital adjustment required under the terms of the agreement with IPH is reflected in "Accounts payable" on the December 31, 2013 Ameren Corporation (parent company only) Condensed Balance Sheet. Assuming IPH and Ameren reach an agreement, both the receivable and the payable will be finalized within 120 days after the closing of the divestiture.
See Note 16 – Divestiture Transactions and Discontinued Operations under Part II, Item 8, of this report for additional information on the impairment charges recognized in 2013 and 2012 as well as the divestiture.

Schedule_II_Valuation_And_Qual

Schedule II - Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts [Abstract]	'
Valuation And Qualifying Accounts	'
	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS
	FOR THE YEARS ENDED DECEMBER 31, 2013, 2012 AND 2011
	(in millions)
	Column A	Column B		Column C				Column D		Column E
	Description	Balance at		-1		-2		Deductions(b)		Balance at End
		Beginning		Charged to Costs		Charged to Other				of Period
		of Period		and Expenses		Accounts(a)
	Ameren:
	Deducted from assets – allowance for doubtful accounts:
	2013	$	17	$	35	$	4	$	38	$	18
	2012	20		30		2		35		17
	2011	23		41		—		44		20
	Deferred tax valuation allowance:
	2013	$	2	$	5	$	—	$	—	$	7
	2012	1		1		—		—		2
	2011	1		—		—		—		1
	Ameren Missouri:
	Deducted from assets – allowance for doubtful accounts:
	2013	$	5	$	16	$	—	$	16	$	5
	2012	7		11		—		13		5
	2011	8		17		—		18		7
	Deferred tax valuation allowance:
	2013	$	1	$	—	$	—	$	—	$	1
	2012	1		—		—		—		1
	2011	1		—		—		—		1
	Ameren Illinois:
	Deducted from assets – allowance for doubtful accounts:
	2013	$	12	$	19	$	4	$	22	$	13
	2012	13		19		2		22		12
	2011	13		24		—		24		13
	Deferred tax valuation allowance:
	2013	$	1	$	—	$	—	$	—	$	1
	2012	—		1		—		—		1
	2011	—		—		—		—		—
	(a)	Uncollectible account reserve associated with receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
	(b)	Uncollectible accounts charged off, less recoveries.

Summary_Of_Significant_Account1

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
General	'
	Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005, administered by FERC. Ameren’s primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of other expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below.
	•	Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri. This area has an estimated population of 2.8 million and includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 127,000 customers.
	•	Ameren Illinois Company, doing business as Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business in Illinois. Ameren Illinois was created by the merger of CILCO and IP with and into CIPS in 2010. CIPS was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to portions of central and southern Illinois having an estimated population of 3.1 million in an area of 40,000 square miles. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 767,000 customers.
	Ameren has various other subsidiaries responsible for activities such as the provision of shared services. Ameren also has a subsidiary, ATXI, that operates a FERC rate-regulated electric transmission business and is developing the Illinois Rivers project.
Consolidation	'
	The financial statements of Ameren are prepared on a consolidated basis, and therefore include the accounts of its majority-owned subsidiaries. Ameren Missouri and Ameren Illinois have no subsidiaries and therefore their financial statements are not prepared on a consolidated basis. All significant intercompany transactions have been eliminated. All tabular dollar amounts are in millions, unless otherwise indicated.
	Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.
Public Utilities	'
	Investments
	Ameren and Ameren Missouri evaluate for impairment the investments held in Ameren Missouri’s nuclear decommissioning trust fund. Losses on assets in the trust fund could result in higher funding requirements for decommissioning costs, which Ameren Missouri believes would be recovered in electric rates paid by its customers. Accordingly, Ameren and Ameren Missouri recognize a regulatory asset on their balance sheets for losses on investments held in the nuclear decommissioning trust fund.
	Purchased Gas, Power and Fuel Rate-adjustment Mechanisms
	Ameren Missouri and Ameren Illinois have various rate-adjustment mechanisms in place that provide for the recovery of purchased natural gas and electric fuel and purchased power costs. See Note 2 – Rate and Regulatory Matters for the regulatory assets and liabilities recorded at December 31, 2013, and 2012, related to the rate-adjustment mechanisms discussed below.
	In Ameren Missouri’s and Ameren Illinois’ retail natural gas utility jurisdictions, changes in natural gas costs are reflected in billings to their natural gas utility customers through PGA clauses. The differences between actual natural gas costs and costs billed to customers in a given period are deferred as regulatory assets or liabilities. The deferred amounts are either billed or refunded to natural gas utility customers in a subsequent period.
	In Ameren Illinois’ retail electric utility jurisdictions, changes in purchased power and transmission service costs are reflected in billings to their electric utility customers through pass-through rate-adjustment clauses. The differences between actual purchased power and transmission service costs and costs billed to customers in a given period are deferred as regulatory assets or liabilities. The deferred amounts are either billed or refunded to electric utility customers in a subsequent period.
	Ameren Missouri has a FAC that allows an adjustment of electric rates three times per year for a pass-through to customers of 95% of changes in fuel, certain fuel additives, emission allowances, purchased power costs, transmission costs and revenues, and MISO costs and revenues, net of off-system sales revenues, greater or less than the amount set in base rates without a traditional rate proceeding, subject to MoPSC prudency review. The differences between the cost of fuel incurred and the cost of fuel recovered from Ameren Missouri customers' base rates are deferred as regulatory assets or liabilities. The deferred amounts are either billed or refunded to Ameren Missouri’s electric utility customers in a subsequent period.
	Accounting for MISO Transactions
	Certain Ameren subsidiaries are regulated by the MoPSC, the ICC, and FERC. In accordance with authoritative accounting guidance regarding accounting for the effects of certain types of regulation, Ameren Missouri and Ameren Illinois defer certain costs as assets pursuant to actions of rate regulators or because of expectations that the companies will be able to recover such costs in rates charged to customers. Ameren Missouri and Ameren Illinois also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be returned to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. In addition to the cost recovery mechanisms discussed in the Purchased Gas, Power and Fuel Rate-adjustment Mechanisms section below, Ameren Missouri and Ameren Illinois have approvals from regulators to use other cost recovery mechanisms. Ameren Missouri has a vegetation management and infrastructure inspection cost tracker, a pension and postretirement benefit cost tracker, an uncertain tax positions tracker, a renewable energy standards cost tracker, a storm restoration cost tracker, and the MEEIA energy efficiency rider. In addition to participating in the IEIMA's formula rate regulatory framework, Ameren Illinois has an environmental cost rider, an asbestos-related litigation rider, an energy efficiency rider, and a bad debt rider. See Note 2 – Rate and Regulatory Matters for additional information on regulatory assets and liabilities. In addition, other costs that Ameren Missouri and Ameren Illinois expect to recover from customers are recorded as construction work in progress and property and plant, net. See Note 3 – Property and Plant, Net.
	Environmental Costs
	Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates. If environmental expenditures are related to facilities currently in use, such as pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset.
Cash and Cash Equivalents	'
	Cash and cash equivalents include cash on hand and temporary investments purchased with an original maturity of three months or less.
Allowance for Doubtful Accounts Receivable	'
	The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has a rate mechanism that adjusts rates for net write-offs of customer accounts receivable above or below those being collected in rates.
Materials and Supplies	'
	Materials and supplies are recorded at the lower of cost or market. Cost is determined using the average-cost method. Materials and supplies are capitalized as inventory when purchased and then expensed or capitalized as plant assets when installed, as appropriate.
Property and Plant	'
	We capitalize the cost of additions to and betterments of units of property and plant. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures, including nuclear refueling and maintenance outages, are expensed as incurred. When units of depreciable property are retired, the original costs, less salvage values, are charged to accumulated depreciation. Asset removal costs accrued by our rate-regulated operations that do not constitute legal obligations are classified as a regulatory liability. See Asset Retirement Obligations below and Note 3 – Property and Plant, Net, for additional information.
	Depreciation
	Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The provision for depreciation for the Ameren Companies in 2013, 2012 and 2011 ranged from 3% to 4% of the average depreciable cost.
Allowance for Funds Used During Construction	'
	e capitalize allowance for funds used during construction, or the cost of borrowed funds and the cost of equity funds (preferred and common stockholders’ equity) applicable to rate-regulated construction expenditures, in accordance with the utility industry's accounting practice. Allowance for funds used during construction does not represent a current source of cash funds. This accounting practice offsets the effect on earnings of the cost of financing during construction, and it treats such financing costs in the same manner as construction charges for labor and materials.
	Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates.
Goodwill and Intangible Assets	'
	Goodwill. Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had recorded goodwill of $411 million at December 31, 2013, and 2012.
	Ameren has two reporting units, which also represent Ameren’s reportable segments. Ameren's reporting units are Ameren Missouri and Ameren Illinois. Ameren Illinois has one reporting unit, Ameren Illinois. Ameren’s and Ameren Illinois' reporting units have been defined and goodwill has been evaluated at the operating segment level in accordance with authoritative accounting guidance. Our reporting units represent businesses for which discrete financial information is available and reviewed regularly by management. All of Ameren's and Ameren Illinois' goodwill at December 31, 2013, and 2012, has been assigned to the Ameren Illinois reporting unit.
	We evaluate goodwill for impairment as of October 31 of each year, or more frequently if events and circumstances indicate that the asset might be impaired. Ameren and Ameren Illinois applied a qualitative goodwill evaluation model for their annual goodwill impairment test conducted as of October 31, 2013. Based on the results of Ameren’s and Ameren Illinois’ qualitative assessment, Ameren and Ameren Illinois believe it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value as of October 31, 2013, indicating no impairment of Ameren’s or Ameren Illinois’ goodwill. The following factors, among others, were considered by Ameren and Ameren Illinois when assessing whether it was more likely than not that the fair value of the Ameren Illinois reporting unit exceeded its carrying value for the October 31, 2013, test:
	•	macroeconomic conditions, including those conditions within Ameren Illinois’ service territory;
	•	pending rate case outcomes and projections of future rate case outcomes;
	•	changes in laws and potential law changes;
	•	observable industry market multiples;
	•	achievement of IEIMA performance metrics and the yield of the 30-year United States treasury bonds; and
	•	actual and forecasted financial performance.
	The goodwill assigned to the Ameren Illinois reporting unit on the December 31, 2013, balance sheets of Ameren and Ameren Illinois had no accumulated goodwill impairment losses. Ameren and Ameren Illinois will continue to monitor the actual and forecasted operating results, cash flows, market capitalization, and observable industry market multiples of the Ameren Illinois reporting unit for signs of possible declines in estimated fair value and potential goodwill impairment.
	Intangible Assets. Ameren and Ameren Missouri classify emission allowances and renewable energy credits as intangible assets. Ameren Illinois consumes renewable energy credits as they are purchased through the IPA procurement process and expenses them immediately. We evaluate intangible assets for impairment if events or changes in circumstances indicate that their carrying amount might be impaired.
	At December 31, 2013, Ameren’s and Ameren Missouri’s intangible assets consisted of renewable energy credits obtained through wind and solar power purchase agreements. The book value of Ameren’s and Ameren Missouri’s renewable energy credits was $22 million and $22 million at December 31, 2013, respectively. The book value of Ameren's and Ameren Missouri's renewable energy credits was $14 million and $14 million at December 31, 2012, respectively.
	Renewable energy credits and emission allowances are charged to purchased power expense and fuel expense, respectively, as they are used in operations.
Impairment of Long-lived Assets	'
	We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets with the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount of the carrying value that exceeds the estimated fair value of the assets. In the period in which we determine an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its fair value less cost to sell.
Unamortized Debt Discount, Premium, And Expense	'
	Discount, premium, and expense associated with long-term debt are amortized over the lives of the related issues.
Revenue	'
	Operating Revenues
	The Ameren Companies record operating revenue for electric or natural gas service when it is delivered to customers. We accrue an estimate of electric and natural gas revenues for service rendered but unbilled at the end of each accounting period.
	Beginning in 2012, Ameren Illinois elected to participate in the performance-based formula ratemaking framework pursuant to the IEIMA. The IEIMA provides for an annual reconciliation of Ameren Illinois' electric distribution revenue requirement. As of each balance sheet date, Ameren Illinois records its estimate of the electric distribution revenue impact resulting from the reconciliation of the revenue requirement necessary to reflect the actual costs incurred for that year with the revenue requirement that was in effect for billing purposes for that year. If the current year's revenue requirement is greater than the revenue requirement customer rates were based upon, an increase to electric operating revenues with an offset to a regulatory asset is recorded to reflect the expected recovery of those additional costs from customers within the next two years. If the current year's revenue requirement is less than the revenue requirement customer rates were based upon, a reduction to electric operating revenues with an offset to a regulatory liability is recorded to reflect the expected refund to customers within the next two years. See Note 2 – Rate and Regulatory Matters for information regarding Ameren Illinois' revenue requirement reconciliation pursuant to the IEIMA.
	Similar to the IEIMA process described above, Ameren Illinois and ATXI record the impact of a revenue requirement reconciliation for each company's electric transmission jurisdiction, pursuant to FERC-approved rate treatment.
Cost Of Sales	'
	Accounting for MISO Transactions
	Ameren Missouri’s cost of nuclear fuel is capitalized and then amortized to fuel expense on a unit-of-production basis. Spent fuel disposal cost is based on net kilowatthours generated and sold. That cost is charged to "Operating Expenses – Fuel" in the statement of income.
Stock-Based Compensation	'
	Stock-based compensation cost is measured at the grant date based on the fair value of the award. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite service period.
Excise Taxes	'
	Excise taxes levied on us are reflected on Ameren Missouri electric customer bills and on Ameren Missouri and Ameren Illinois natural gas customer bills. They are recorded gross in “Operating Revenues – Electric,” “Operating Revenues – Gas” and “Operating Expenses – Taxes other than income taxes” on the statement of income (loss). Excise taxes reflected on Ameren Illinois electric customer bills are imposed on the customer and are therefore not included in revenues and expenses. They are included in “Taxes accrued” on the balance sheet.
Income Taxes	'
	Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes, in accordance with authoritative accounting guidance. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates.
	We recognize that regulators will probably reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in the deferred tax liability, which were recorded because of decreases in the statutory rate, have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery in rates of future income taxes, resulting from the reversal of the equity portion of the allowance for funds used during construction that was an unrecognized temporary difference prior to the adoption of the authoritative accounting guidance for income taxes.
	Investment tax credits used on tax returns for prior years have been deferred in accordance with GAAP. The credits are being amortized over the useful lives of the related investment. Deferred income taxes were recorded on the temporary difference represented by the deferred investment tax credits and a corresponding regulatory liability. This recognizes the expected reduction in rate revenue for future lower income taxes associated with the amortization of the investment tax credits. See Note 13 – Income Taxes.
	For certain renewable energy construction projects placed in service, Ameren Missouri elected to seek federal tax grants in lieu of the investment tax credits for which the projects also qualified. These grants were accounted for using a grant recognition accounting model. Ameren Missouri elected to reduce the basis of property as grants were received, which will reduce the amount of depreciation expense recognized in future periods. In 2012, Ameren Missouri received $18 million in federal tax grants.
	Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax similar to that which would be owed had the party been separately subject to tax. Any net benefit attributable to the parent is reallocated to other members. That allocation is treated as a contribution of capital to the party receiving the benefit.
Noncontrolling Interest	'
	Ameren’s noncontrolling interests included the preferred stock not subject to mandatory redemption of Ameren Missouri and Ameren Illinois. As of December 31, 2012, Ameren's noncontrolling interests also included the 20% of EEI not owned by Ameren. All noncontrolling interests are classified as a component of equity separate from Ameren’s equity in its consolidated balance sheet.
Earnings Per Share	'
	Earnings per Share
	Basic earnings per share is computed by dividing net income attributable to Ameren Corporation by the weighted-average number of common shares outstanding during the period. Diluted earnings per share is computed by dividing net income attributable to Ameren Corporation by the diluted weighted-average number of common shares outstanding during the period. Diluted earnings per share reflects the potential dilution that would occur if certain stock-based performance share units were settled.
Accounting Changes and Other Matters	'
	Accounting Changes and Other Matters
	The following is a summary of recently adopted authoritative accounting guidance, as well as guidance issued but not yet adopted, that could affect the Ameren Companies.
	Presentation of Comprehensive Income
	In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance changed the presentation of comprehensive income in the financial statements. It requires entities to report components of comprehensive income either in a continuous statement of comprehensive income or in two separate but consecutive statements. This guidance was effective for the Ameren Companies beginning in the first quarter of 2012 with retroactive application required. The implementation of the amended guidance did not affect the Ameren Companies’ results of operations, financial position, or liquidity.
	In February 2013, FASB amended this guidance to require an entity to provide information about the amounts reclassified out of accumulated OCI by component. In addition, an entity is required to present significant amounts reclassified out of accumulated OCI by the respective line items of net income either on the face of the statement where net income is presented or in the footnotes. This guidance was effective for the Ameren Companies beginning in the first quarter of 2013. The implementation of this amended guidance did not affect the Ameren Companies’ results of operations, financial position, or liquidity. The amounts reclassified out of accumulated OCI for the Ameren Companies corresponding to continuing operations related to pension and other postretirement plan activity. These amounts were immaterial for the year ended December 31, 2013, and therefore no additional disclosures were required.
	Disclosures about Offsetting Assets and Liabilities
	In December 2011, FASB issued additional authoritative accounting guidance to improve information disclosed about financial and derivative instruments. The guidance requires an entity to disclose information about offsetting and related arrangements to enable users of the financial statements to understand the effect of those arrangements on its financial position. In January 2013, FASB amended this guidance to limit the scope to derivative instruments, repurchase agreements and reverse repurchase agreements, and securities borrowing and securities lending transactions. The Ameren Companies adopted this guidance for the first quarter of 2013. The implementation of this additional guidance did not affect the Ameren Companies’ results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. See Note 7 – Derivative Financial Instruments for the required additional disclosures.
	Presentation of an Unrecognized Tax Benefit
	In July 2013, FASB issued additional authoritative accounting guidance to provide clarity for the financial statement presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exists. It requires entities to present an unrecognized tax benefit as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward to the extent a net operating loss carryforward, a similar tax loss, or a tax credit carryforward is available under the tax law. Currently, any unrecognized tax benefit is recorded in “Other deferred credits and liabilities” on Ameren's, Ameren Missouri's, and Ameren Illinois' balance sheets. After this guidance becomes effective, any unrecognized tax benefit will be recorded in “Accumulated deferred income taxes, net” as a reduction to the deferred tax assets for net operating loss, a similar tax loss, and tax credit carryforwards on the respective balance sheets. At December 31, 2013, unrecognized tax benefits of $48 million and $15 million would have been recorded in “Accumulated deferred income taxes, net” at Ameren and Ameren Missouri, respectively under this new guidance. To the extent that an unrecognized tax benefit exceeds these carryforwards, the excess would continue to be recorded in “Other deferred credits and liabilities” on the respective balance sheets, consistent with current authoritative accounting guidance. The amended guidance will not affect the Ameren Companies' results of operations or liquidity, as this guidance is presentation-related only. This guidance will be effective for the Ameren Companies beginning in the first quarter of 2014.
Asset Retirement Obligations	'
	Authoritative accounting guidance requires us to record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and to capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we are required to make adjustments to AROs based on changes in the estimated fair values of the obligations. Corresponding increases in asset book values are depreciated over the remaining useful life of the related asset. Uncertainties as to the probability, timing, or amount of cash flows associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with Ameren Missouri’s Callaway energy center decommissioning costs, asbestos removal, CCR storage facilities, and river structures. Also, Ameren and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal. In addition, Ameren, Ameren Missouri and Ameren Illinois have recorded AROs for the disposal of certain transformers.
	Asset removal costs accrued by our rate-regulated operations that do not constitute legal obligations are classified as a regulatory liability.

Summary_Of_Significant_Account2

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Schedule Of Materials And Supplies	'
	The following table presents a breakdown of materials and supplies for each of the Ameren Companies at December 31, 2013, and 2012:
			Ameren Missouri				Ameren Illinois				Ameren
	2013
	Fuel(a)		$	144			$	—			$	144
	Gas stored underground		17				110				127
	Other materials and supplies		191				64				255
			$	352			$	174			$	526
	2012
	Fuel(a)		$	198			$	—			$	198
	Gas stored underground		18				113				131
	Other materials and supplies		181				60				241
			$	397			$	173			$	570
	(a)	Consists of coal, oil, and propane.
Schedule Of Rates Used For Allowance For Funds Used During Construction	'
	The following table presents the annual allowance for funds used during construction rates that were utilized during 2013, 2012 and 2011:
		2013			2012			2011
	Ameren Missouri	8	%		8	%		8	%
	Ameren Illinois	8	%		9	%		9	%
Schedule Of Amortization Based On Usage Of Renewable Energy Credits And Emission Allowances	'
			2013			2012			2011
	Ameren Missouri	$	(a)		$	(a)		$	(a)
	Ameren Illinois		13			4			3
	Ameren	$	13		$	4		$	3
	(a)	Less than $1 million.
Schedule Of Excise Taxes	'
	The following table presents excise taxes recorded in “Operating Revenues – Electric,” “Operating Revenues – Gas,” and “Operating Expenses – Taxes other than income taxes” for the years ended 2013, 2012 and 2011:
		2013				2012				2011
	Ameren Missouri	$	152			$	139			$	137
	Ameren Illinois	61				54				57
	Ameren	$	213			$	193			$	194
Schedule of Earnings Per Share, Basic and Diluted	'
	The following table presents Ameren’s basic and diluted earnings per share calculations and reconciles the weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the years ended December 31, 2013, 2012 and 2011:
		2013				2012				2011
	Net income (loss) attributable to Ameren Corporation:
	Continuing operations	$	512			$	516			$	431
	Discontinued operations	(223		)		(1,490		)		88
	Net income (loss) attributable to Ameren Corporation	$	289			$	(974	)		$	519
	Average common shares outstanding – basic	242.6				242.6				241.5
	Assumed settlement of performance share units	1.9				0.4				0.6
	Average common shares outstanding – diluted	244.5				243				242.1
	Earnings (loss) per common share – basic:
	Continuing operations	$	2.11			$	2.13			$	1.79
	Discontinued operations	(0.92		)		(6.14		)		0.36
	Earnings (loss) per common share – basic	$	1.19			$	(4.01	)		$	2.15
	Earnings (loss) per common share – diluted:
	Continuing operations	$	2.1			$	2.13			$	1.79
	Discontinued operations	(0.92		)		(6.14		)		0.36
	Earnings (loss) per common share – diluted	$	1.18			$	(4.01	)		$	2.15
	Average performance share units excluded from calculation(a)	0.1				0.7				—
	(a)	Weighted-average number of performance share units that were excluded from the “Assumed settlement of performance share units” provided above because the performance or market conditions related to the awards had not yet been met.
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	'
	The following table presents additional information regarding Ameren's consolidated statement of cash flows for the years ended December 31, 2013, 2012 and 2011:
		2013				2012				2011
	Cash paid (refunded) during the year:
	Interest
	Continuing operations(a)	$	362			$	384			$	393
	Discontinued operations(b)	31				49				60
		$	393			$	433			$	453
	Income taxes, net
	Continuing Operations	$	116			$	10			$	(47	)
	Discontinued Operations	(108		)		(9		)		(14		)
		$	8			$	1			$	(61	)
	(a)	Net of $20 million, $17 million, and $27 million capitalized, respectively.
	(b)	Net of $17 million, $13 million, and $3 million capitalized, respectively.
Schedule Of Asset Retirement Obligations	'
	The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2013, and 2012:
		Ameren				Ameren				Ameren(a)
		Missouri(a)				Illinois(b)
	Balance at December 31, 2011	$	328			$	3			$	331
	Liabilities incurred	—				—				—
	Liabilities settled	(1		)		(c)				(1		)
	Accretion in 2012(d)	18				(c)				18
	Change in estimates(e)	1				(c)				1
	Balance at December 31, 2012	$	346			$	3			$	349
	Liabilities incurred	—				—				—
	Liabilities settled	(1		)		(c)				(1		)
	Accretion in 2013(d)	19				(c)				19
	Change in estimates(e)	2				(c)				2
	Balance at December 31, 2013	$	366			$	3			$	369
	(a)	The nuclear decommissioning trust fund assets of $494 million and $408 million as of December 31, 2013, and 2012, respectively, are restricted for decommissioning of the Callaway energy center.
	(b)	Balance included in “Other deferred credits and liabilities” on the balance sheet.
	(c)	Less than $1 million.
	(d)	Accretion expense was recorded as an increase to regulatory assets at Ameren Missouri and Ameren Illinois.
	(e)	Ameren Missouri changed its fair value estimates for asbestos removal in 2012 and 2013, and for certain CCR storage facilities in 2013.
	See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the AROs related to the abandoned Meredosia and Hutsonville energy centers, which are presented as discontinued operations and therefore not included in the table above.

Rate_And_Regulatory_Matters_Ta

Rate And Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2013
Public Utilities, General Disclosures [Abstract]	'
Schedule Of Regulatory Assets And Liabilities	'
	The following table presents Ameren’s, Ameren Missouri’s and Ameren Illinois’ regulatory assets and regulatory liabilities at December 31, 2013, and 2012:
			2013						2012
			Ameren		Ameren		Ameren			Ameren		Ameren		Ameren
			Missouri		Illinois					Missouri		Illinois
	Current regulatory assets:
	Under-recovered FAC(a)(b)		$	104	$	—	$	104		$	145	$	—	$	145
	Under-recovered Illinois electric power costs(c)		—		1		1			—		—		—
	Under-recovered PGA(c)		—		1		1			5		7		12
	MTM derivative losses(d)		14		36		50			13		77		90
	Total current regulatory assets		$	118	$	38	$	156		$	163	$	84	$	247
	Noncurrent regulatory assets:
	Pension and postretirement benefit costs(e)		$	44	$	140	$	184		$	348	$	424	$	772
	Income taxes(f)		230		7		237			231		4		235
	Asset retirement obligations(g)		—		5		5			—		5		5
	Callaway costs(a)(h)		40		—		40			44		—		44
	Unamortized loss on reacquired debt(a)(i)		77		74		151			81		100		181
	Recoverable costs – contaminated facilities(j)		—		271		271			—		248		248
	MTM derivative losses(d)		8		118		126			7		128		135
	Storm costs(k)		5		3		8			9		—		9
	Demand-side costs before MEEIA implementation(a)(l)		58		—		58			73		—		73
	Reserve for workers’ compensation liabilities(m)		6		6		12			6		6		12
	Credit facilities fees(n)		5		—		5			6		—		6
	Common stock issuance costs(o)		4		—		4			7		—		7
	Construction accounting for pollution control equipment(a)(p)		22		—		22			23		—		23
	Solar rebate program(a)(q)		27		—		27			5		—		5
	IEIMA revenue requirement reconciliation(r)		—		65		65			—		—		—
	Other(s)(t)		8		12		25			12		19		31
	Total noncurrent regulatory assets		$	534	$	701	$	1,240		$	852	$	934	$	1,786
	Current regulatory liabilities:
	Over-recovered FAC(b)		$	26	$	—	$	26		$	—	$	—	$	—
	Over-recovered Illinois electric power costs(c)		—		51		51			—		58		58
	Over-recovered PGA(c)		5		29		34			—		15		15
	MTM derivative gains(d)		26		1		27			18		1		19
	Wholesale distribution refund(u)		—		13		13			—		8		8
	IEIMA revenue requirement reconciliation(r)		—		65		65			—		—		—
	Total current regulatory liabilities		$	57	$	159	$	216		$	18	$	82	$	100
	Noncurrent regulatory liabilities:
	Income taxes(v)		$	38	$	3	$	41		$	42	$	4	$	46
	Removal costs(w)		828		610		1,438			766		581		1,347
	Asset retirement obligation(g)		146		—		146			80		—		80
	MTM derivative gains(d)		1		—		1			2		—		2
	Bad debt riders(x)		—		8		8			—		12		12
	Pension and postretirement benefit costs tracker(y)		15		—		15			23		—		23
	Energy efficiency riders(z)		3		33		36			—		20		20
	IEIMA revenue requirement reconciliation(r)		—		—		—			—		55		55
	FERC transmission revenue requirement reconciliation(aa)		—		10		10			—		—		—
	Other(ab)		10		—		10			4		—		4
	Total noncurrent regulatory liabilities		$	1,041	$	664	$	1,705		$	917	$	672	$	1,589
	(a)	These assets earn a return.
	(b)	Under-recovered or over-recovered fuel costs to be recovered through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from customers that occurs over the next eight months.
	(c)	Costs under- or over-recovered from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.
	(d)	Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.
	(e)	These costs are being amortized in proportion to the recognition of prior service costs (credits), transition obligations (assets), and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 11 – Retirement Benefits for additional information.
	(f)	Offset to certain deferred tax liabilities for expected recovery of future income taxes when paid. This will be recovered over the expected life of the related assets.
	(g)	Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.
	(h)	Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the remaining life of the energy center's current operating license, which expires in 2024.
	(i)	Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.
	(j)	The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 15 – Commitments and Contingencies for additional information.
	(k)	Actual storm costs in a test year that exceed the MoPSC staff’s normalized storm costs for rate purposes. As approved by the December 2012 MoPSC electric rate order, the 2006, 2007, and 2008 storm costs are being amortized through December 2014. As approved by the May 2010 MoPSC electric rate order, the 2009 storm costs are being amortized through June 2015. The Ameren Illinois total includes 2013 storm costs deferred in accordance with the IEIMA. These costs are being amortized over a five-year period beginning in 2013.
	(l)	Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized over a six-year period that began in July 2010. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013.
	(m)	Reserve for workers’ compensation claims. The period of recovery will depend on the timing of actual expenditures.
	(n)	Ameren Missouri’s costs incurred to enter into and maintain the 2012 Ameren Missouri Credit Agreement. These costs are being amortized over five years, beginning in November 2012. These costs are being amortized to construction work in progress, which will be depreciated when assets are placed into service.
	(o)	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to recover its portion of Ameren’s September 2009 common stock issuance costs. These costs are being amortized over five years, beginning in July 2010.
(p)	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment could be included in customer rates. These costs will be amortized over the expected life of the Sioux energy center, which is currently through 2033.
(q)	Costs associated with Ameren Missouri's solar rebate program beginning in August 2012 to fulfill Ameren Missouri's renewable energy portfolio requirement. The amortization period for these costs will be three years, commencing with the next Ameren Missouri electric rate case order.
(r)	The asset balance relates to the difference between Ameren Illinois' 2013 revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework, and the revenue requirement included in customer rates for 2013. Subject to ICC approval, this asset will be collected from customers in 2015. The liability balance relates to the difference between Ameren Illinois' 2012 revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for 2012. This liability will be refunded to customers in 2014.
(s)	The Ameren Illinois total includes Ameren Illinois Merger integration and optimization costs, which are amortized over four years, beginning in January 2012. The Ameren Illinois total also includes costs related to the 2013 natural gas delivery service rate case costs, which are being amortized over a two-year period that began in January 2014. The Ameren Illinois total also includes a portion of the unamortized debt fair value adjustment recorded upon Ameren's acquisition of IP. This portion is being amortized over the remaining life of the related debt. At Ameren Missouri, the balance primarily includes the cost of renewable energy credits to fulfill its renewable energy portfolio requirement. Costs incurred from January 2010 through July 2012 are being amortized over three years, beginning in January 2013.
(t)	The Ameren total includes $5 million for ATXI's revenue requirement reconciliation adjustments for 2012 and 2013 calculated pursuant to the FERC's electric transmission formula ratemaking framework. These adjustments will be collected from customers in 2014 for the 2012 revenue requirement reconciliation and in 2015 for the 2013 revenue requirement reconciliation.
(u)	Estimated refund to wholesale electric customers. See 2011 Wholesale Distribution Rate Case above.
(v)	Unamortized portion of investment tax credits, federal excess deferred taxes, and uncertain tax position tracker. The tracker is being amortized over three years, beginning in January 2013. The unamortized portion of investment tax credit is being amortized over the expected life of the underlying assets.
(w)	Estimated funds collected for the eventual dismantling and removal of plant from service, net of salvage value, upon retirement related to our rate-regulated operations.
(x)	A regulatory tracking mechanism for the difference between the level of bad debt expense incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2011 was refunded to customers from June 2012 through May 2013. The over-recovery relating to 2012 is being refunded to customers from June 2013 through May 2014. The over-recovery relating to 2013 will be refunded to customers from June 2013 through May 2014.
(y)	A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs built into rates. For periods prior to August 2012, the MoPSC's December 2012 electric rate order directed the amortization to occur over five years, beginning in January 2013. For periods after August 2012, the amortization period will be determined in a future Ameren Missouri electric rate case.
(z)	The Ameren Illinois balance relates its regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. This over-recovery will be refunded to customers over the following 12 months after the plan year. The Ameren Missouri balance relates to its MEEIA program costs incurred and projected lost revenues compared to the amount previously collected from customers. Beginning in January 2014, a MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the projected amounts collected from customers for the MEEIA program costs and its projected lost revenues. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs and projected lost revenues are incurred.
(aa)	Ameren Illinois' 2013 revenue requirement reconciliation adjustment calculated pursuant to the FERC's electric transmission formula ratemaking framework. This liability will be refunded to customers in 2015.
(ab)	Balance primarily includes the costs of renewable energy credits to fulfill Ameren Missouri's renewable energy portfolio requirement from August 2012 through December 2013, which were less than the amount included in rates. The amortization period for this over-recovery will be determined in a future Ameren Missouri electric rate case.

Property_And_Plant_Net_Tables

Property And Plant, Net (Tables)	12 Months Ended
	Dec. 31, 2013
Property, Plant and Equipment [Abstract]	'
Schedule Of Property And Plant, Net	'
	The following table presents property and plant, net, for each of the Ameren Companies at December 31, 2013, and 2012:
			Ameren			Ameren			Other		Ameren(a)(b)
			Missouri(a)			Illinois
	2013
	Property and plant, at original cost:
	Electric		$	15,964		$	5,426		$	336	$	21,726
	Natural gas		413			1,562			—		1,975
			16,377			6,988			336		23,701
	Less: Accumulated depreciation and amortization		6,766			1,627			251		8,644
			9,611			5,361			85		15,057
	Construction work in progress:
	Nuclear fuel in process		246			—			—		246
	Other		595			228			79		902
	Property and plant, net		$	10,452		$	5,589		$	164	$	16,205
	2012
	Property and plant, at original cost:
	Electric		$	15,638		$	4,985		$	319	$	20,942
	Natural gas		393			1,461			—		1,854
			16,031			6,446			319		22,796
	Less: Accumulated depreciation and amortization		6,614			1,495			237		8,346
			9,417			4,951			82		14,450
	Construction work in progress:
	Nuclear fuel in process		317			—			—		317
	Other		427			101			53		581
	Property and plant, net		$	10,161		$	5,052		$	135	$	15,348
	(a)	Amounts in Ameren and Ameren Missouri include two electric generation CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $228 million at December 31, 2013, and $228 million at December 31, 2012. The total accumulated depreciation associated with the two CTs was $56 million and $52 million at December 31, 2013, and 2012, respectively. In addition, Ameren Missouri has investments in debt securities, which were classified as held-to-maturity, related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2013, and 2012, the carrying value of these debt securities was $299 million and $304 million, respectively.
	(b)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Accrued Capital Expenditures	'
	The following table provides accrued capital and nuclear fuel expenditures at December 31, 2013, 2012, and 2011, which represent noncash investing activity excluded from the accompanying statements of cash flows:
		Ameren(a)			Ameren			Ameren
					Missouri			Illinois
	Accrued capital expenditures:
	2013	$	175		$	74		$	86
	2012	107			63			37
	2011	97			73			18
	Accrued nuclear fuel expenditures:
	2013	8			8			(b)
	2012	8			8			(b)
	2011	36			36			(b)
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

ShortTerm_Debt_And_Liquidity_T

Short-Term Debt And Liquidity (Tables)	12 Months Ended
	Dec. 31, 2013
Line of Credit Facility [Abstract]	'
Schedule Of Maximum Aggregate Amount Available On Credit Agreements	'
	The maximum aggregate amount available to each borrower under each facility is shown in the following table (such amount being such borrower's "Borrowing Sublimit"):
			2012 Missouri Credit Agreement		2012 Illinois
					Credit Agreement
	Ameren	$	500		$	300
	Ameren Missouri		800		(a)
	Ameren Illinois		(a)		800
	(a)	Not applicable.
Schedule of Commercial Paper	'
	mercial Paper
	The following table summarizes the borrowing activity and relevant interest rates under Ameren's commercial paper program, for the years ended December 31, 2013, and 2012:
			2013				2012
	Average daily borrowings outstanding		$	54			$	49
	Outstanding borrowings at period-end		368				—
	Weighted-average interest rate		0.56		%		0.92		%
	Peak borrowings during period		$	368			$	229
	Peak interest rate		0.85		%		1.25		%

LongTerm_Debt_And_Equity_Finan1

Long-Term Debt And Equity Financings (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Instrument [Line Items]	'
Schedule of Long-term Debt Instruments	'
	The following table presents long-term debt outstanding, including maturities due within one year, for the Ameren Companies as of December 31, 2013, and 2012:
		2013				2012
	Ameren (Parent):
	8.875% Senior unsecured notes due 2014	$	425			$	425
	Less: Unamortized discount and premium	—				(1		)
	Less: Maturities due within one year	(425		)		—
	Long-term debt, net	$	—			$	424
	Ameren Missouri:
	Senior secured notes:(a)
	4.65% Senior secured notes due 2013	—				200
	5.50% Senior secured notes due 2014	104				104
	4.75% Senior secured notes due 2015	114				114
	5.40% Senior secured notes due 2016	260				260
	6.40% Senior secured notes due 2017	425				425
	6.00% Senior secured notes due 2018(b)	179				179
	5.10% Senior secured notes due 2018	199				199
	6.70% Senior secured notes due 2019(b)	329				329
	5.10% Senior secured notes due 2019	244				244
	5.00% Senior secured notes due 2020	85				85
	5.50% Senior secured notes due 2034	184				184
	5.30% Senior secured notes due 2037	300				300
	8.45% Senior secured notes due 2039(b)	350				350
	3.90% Senior secured notes due 2042(b)	485				485
	Environmental improvement and pollution control revenue bonds:
	1992 Series due 2022(c)(d)	47				47
	1993 5.45% Series due 2028(e)	(e)				44
	1998 Series A due 2033(c)(d)	60				60
	1998 Series B due 2033(c)(d)	50				50
	1998 Series C due 2033(c)(d)	50				50
	Capital lease obligations:
	City of Bowling Green capital lease (Peno Creek CT) through 2022	59				64
	Audrain County capital lease (Audrain County CT) due 2023	240				240
	Total long-term debt, gross	3,764				4,013
	Less: Unamortized discount and premium	(7		)		(7		)
	Less: Maturities due within one year	(109		)		(205		)
	Long-term debt, net	$	3,648			$	3,801
		2013				2012
	Ameren Illinois:
	Senior secured notes:
	8.875% Senior secured notes due 2013(f)	$	—			$	150
	6.20% Senior secured notes due 2016(f)	54				54
	6.25% Senior secured notes due 2016(g)	75				75
	6.125% Senior secured notes due 2017(g)(h)	250				250
	6.25% Senior secured notes due 2018(g)(h)	144				144
	9.75% Senior secured notes due 2018(g)(h)	313				313
	2.70% Senior secured notes due 2022(g)(h)	400				400
	6.125% Senior secured notes due 2028(g)	60				60
	6.70% Senior secured notes due 2036(g)	61				61
	6.70% Senior secured notes due 2036(f)	42				42
	4.80% Senior secured notes due 2043(g)	280				—
	Environmental improvement and pollution control revenue bonds:
	5.90% Series 1993 due 2023(i)	32				32
	5.70% 1994A Series due 2024(j)	36				36
	1993 Series C-1 5.95% due 2026(k)	35				35
	1993 Series C-2 5.70% due 2026(k)	8				8
	1993 Series B-1 due 2028(d)(k)	17				17
	5.40% 1998A Series due 2028(j)	19				19
	5.40% 1998B Series due 2028(j)	33				33
	Fair-market value adjustments	4				4
	Total long-term debt, gross	1,863				1,733
	Less: Unamortized discount and premium	(7		)		(6		)
	Less: Maturities due within one year	—				(150		)
	Long-term debt, net	$	1,856			$	1,577
Ameren consolidated long-term debt, net	$	5,504			$	5,802
(a)	These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.
(b)	Ameren Missouri has agreed, during the life of these notes, not to optionally redeem, purchase or otherwise retire in full its first mortgage bonds. Ameren Missouri has also agreed to prevent a first mortgage bond release date from occurring as long as any of the 8.45% senior secured notes due 2039 and any of the 3.90% senior secured notes due 2042 remain outstanding.
(c)	These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri's senior secured notes. The bonds are also backed by an insurance guarantee policy.
(d)	Interest rates, and periods during which such rates apply, vary depending on our selection of defined rate modes. Maximum interest rates could range up to 18% depending on the series of bonds. The average interest rates for 2013 and 2012 were as follows:
	2013		2012
Ameren Missouri 1992 Series	0.17%		0.30%
Ameren Missouri 1998 Series A	0.34%		0.65%
Ameren Missouri 1998 Series B	0.33%		0.64%
Ameren Missouri 1998 Series C	0.34%		0.64%
Ameren Illinois 1993 Series B-1	0.14%		0.22%
(e)	These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.
(f)	These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the CILCO mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the CILCO first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2023.
(g)	These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.
(h)	Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.
(i)	These bonds are first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture and are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value.
(j)	These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy.
(k)	The bonds are callable at 100% of par value.
Schedule Of Maturities Of Long-Term Debt	'
	The following table presents the aggregate maturities of long-term debt, including current maturities, for the Ameren Companies at December 31, 2013:
		Ameren				Ameren				Ameren				Ameren
		(Parent)(a)				Missouri(a)				Illinois(a)(b)				Consolidated
	2014	$	425			$	109			$	—			$	534
	2015	—				120				—				120
	2016	—				266				129				395
	2017	—				431				250				681
	2018	—				383				457				840
	Thereafter	—				2,455				1,023				3,478
	Total	$	425			$	3,764			$	1,859			$	6,048
	(a)	Excludes unamortized discount and premium of $7 million and $7 million at Ameren Missouri and Ameren Illinois, respectively.
	(b)	Excludes $4 million related to Ameren Illinois’ long-term debt fair-market value adjustments, which are being amortized to interest expense over the remaining life of the debt.
Schedule Of Outstanding Preferred Stock	'
				Redemption Price(per share)				2013				2012
	Ameren Missouri:
	Without par value and stated value of $100 per share, 25 million shares authorized
	$3.50 Series	130,000 shares		$	110			$	13			$	13
	$3.70 Series	40,000 shares		104.75				4				4
	$4.00 Series	150,000 shares		105.625				15				15
	$4.30 Series	40,000 shares		105				4				4
	$4.50 Series	213,595 shares		110			(a)	21				21
	$4.56 Series	200,000 shares		102.47				20				20
	$4.75 Series	20,000 shares		102.176				2				2
	$5.50 Series A	14,000 shares		110				1				1
	Total							$	80			$	80
	Ameren Illinois:
	With par value of $100 per share, 2 million shares authorized
	4.00% Series	144,275 shares		$	101			$	14			$	14
	4.08% Series	45,224 shares		103				5				5
	4.20% Series	23,655 shares		104				2				2
	4.25% Series	50,000 shares		102				5				5
	4.26% Series	16,621 shares		103				2				2
	4.42% Series	16,190 shares		103				2				2
	4.70% Series	18,429 shares		103				2				2
	4.90% Series	73,825 shares		102				7				7
	4.92% Series	49,289 shares		103.5				5				5
	5.16% Series	50,000 shares		102				5				5
	6.625% Series	124,274 shares		100				12				12
	7.75% Series	4,542 shares		100				1				1
	Total							$	62			$	62
	Total Ameren							$	142			$	142
	(a)	In the event of voluntary liquidation, $105.50.
Schedule of Required and Actual Debt Ratios	'
	The following table summarizes the required and actual interest coverage ratios for interest charges and dividend coverage ratios and bonds and preferred stock issuable as of December 31, 2013, at an assumed interest rate of 6% and dividend rate of 7%.
		Required Interest	Actual Interest		Bonds Issuable(b)				Required Dividend	Actual Dividend		Preferred Stock
		Coverage Ratio(a)	Coverage Ratio						Coverage Ratio(c)	Coverage Ratio		Issuable
	Ameren Missouri	>2.0	4.5		$	3,831			>2.5	116.5		$	2,228
	Ameren Illinois	>2.0	6.8		3,565			(d)	>1.5	2.4		203
	(a)	Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.
	(b)	Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $729 million and $365 million at Ameren Missouri and Ameren Illinois, respectively.
	(c)	Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.
	(d)	Amount of bonds issuable by Ameren Illinois based on unfunded property additions and retired bonds solely under the former IP mortgage indenture.
Union Electric Company	'
Debt Instrument [Line Items]	'
Aggregate Principal Amount Of Maturities	'
	The following table sets forth the aggregate principal amount of each series of notes repurchased, along with certain other items related to the tender offer:
	Senior Secured Notes	Principal Amount Repurchased				Premium Plus Accrued				Principal Amount Outstanding After Tender Offer
						and Unpaid Interest(a)
	6.00% senior secured notes due 2018	$	71			$	19			$	179
	6.70% senior secured notes due 2019	121				35				329
	5.10% senior secured notes due 2018	1				(b)				199
	5.10% senior secured notes due 2019	56				12				244
	(a)	The premiums paid in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $485 million 3.90% senior secured notes due 2042.
	(b)	Amount is less than $1 million.
Ameren Illinois Company	'
Debt Instrument [Line Items]	'
Debt Redemption [Table Text Block]	'
	In January 2014, Ameren Illinois redeemed the following environmental improvement and pollution control revenue bonds at par value plus accrued interest:
	Senior Secured Notes	Principal Amount
	5.90% Series 1993 due 2023(a)	$	32
	5.70% 1994A Series due 2024(a)	36
	1993 Series C-1 5.95% due 2026	35
	1993 Series C-2 5.70% due 2026	8
	5.40% 1998A Series due 2028	19
	5.40% 1998B Series due 2028	33
	Total amount redeemed	$	163
	(a)	Less than $1 million principal amount of the bonds remain outstanding as of January 31, 2014.
Aggregate Principal Amount Of Maturities	'
	The following table sets forth the aggregate principal amount of each series of notes repurchased, along with certain other items related to the tender offer:
	Senior Secured Notes	Principal Amount Repurchased				Premium Plus Accrued				Principal Amount Outstanding After Tender Offer
						and Unpaid Interest(a)
	9.75% senior secured notes due 2018	$	87			$	36			$	313
	6.25% senior secured notes due 2018	194				47				144
	(a)	Premiums paid in the amount of $21 million in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $400 million 2.70% senior secured notes due 2022.

Other_Income_And_Expenses_Tabl

Other Income And Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Other Nonoperating Income (Expense) [Abstract]	'
Other Income And Expenses	'
	The following table presents the components of "Other Income and Expenses" in the Ameren Companies’ statements of income (loss) for the years ended December 31, 2013, 2012, and 2011:
		2013		2012			2011
	Ameren:(a)
	Miscellaneous income:
	Allowance for equity funds used during construction	$	37	$	36		$	34
	Interest income on industrial development revenue bonds	27		28			28
	Interest and dividend income	3		4		(b)	3
	Other	2		2			3
	Total miscellaneous income	$	69	$	70		$	68
	Miscellaneous expense:
	Donations	$	12	$	24	(c)	$	8
	Other	14		13			15
	Total miscellaneous expense	$	26	$	37		$	23
	Ameren Missouri:
	Miscellaneous income:
	Allowance for equity funds used during construction	$	31	$	31		$	30
	Interest income on industrial development revenue bonds	27		28			28
	Interest and dividend income	—		4		(b)	2
	Other	—		—			1
	Total miscellaneous income	$	58	$	63		$	61
	Miscellaneous expense:
	Donations	$	4	$	9		$	3
	Other	7		5			7
	Total miscellaneous expense	$	11	$	14		$	10
	Ameren Illinois:
	Miscellaneous income:
	Allowance for equity funds used during construction	$	6	$	5		$	4
	Interest and dividend income	2		—			1
	Other	2		2			2
	Total miscellaneous income	$	10	$	7		$	7
	Miscellaneous expense:
	Donations	$	4	$	11	(c)	$	1
	Other	5		6			5
	Total miscellaneous expense	$	9	$	17		$	6
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	Includes interest income received in 2012 relating to a refund of charges included in an expired power purchase agreement with Entergy. See Note 2 – Rate and Regulatory Matters for additional information.
	(c)	Includes Ameren Illinois' one-time $7.5 million donation to the Illinois Science and Energy Innovation Trust pursuant to the IEIMA as a result of Ameren Illinois' 2012 participation in the electric delivery formula ratemaking process.

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2013
Derivative Instrument Detail [Abstract]	'
Open Gross Derivative Volumes By Commodity Type	'
	The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2013, and 2012. As of December 31, 2013, these contracts ran through October 2016, October 2019, May 2032, and October 2016 for fuel oils, natural gas, power, and uranium, respectively.
		Quantity (in millions, except as indicated)
		2013			2012
	Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
	Fuel oils (in gallons)(a)	66	(b)	66	70	(b)	70
	Natural gas (in mmbtu)	28	108	136	19	128	147
	Power (in megawatthours)	3	11	14	11	14	25
	Uranium (pounds in thousands)	796	(b)	796	446	(b)	446
	(a)	Fuel oils consist of heating oil, ultra-low-sulfur diesel, and crude oil.
	(b)	Not applicable.
Derivative Instruments Carrying Value	'
	The following table presents the carrying value and balance sheet location of all derivative instruments as of December 31, 2013, and 2012:
		Balance Sheet Location		Ameren			Ameren			Ameren
				Missouri			Illinois
	2013
	Derivative assets not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	Other current assets	$	6		$	—		$	6
		Other assets		3			—			3
	Natural gas	Other current assets		1			1			2
	Power	Other current assets		23			—			23
		Total assets	$	33		$	1		$	34
	Derivative liabilities not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	MTM derivative liabilities	$	(b)		$	—		$	2
		Other current liabilities		2			—			—
		Other deferred credits and liabilities		1			—			1
	Natural gas	MTM derivative liabilities		(b)			27			32
		Other current liabilities		5			—			—
		Other deferred credits and liabilities		6			19			25
	Power	MTM derivative liabilities		(b)			9			13
		Other current liabilities		4			—			—
		Other deferred credits and liabilities		—			99			99
	Uranium	MTM derivative liabilities		(b)			—			5
		Other current liabilities		5			—			—
		Other deferred credits and liabilities		1			—			1
		Total liabilities	$	24		$	154		$	178
	2012
	Derivative assets not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	Other current assets	$	8		$	—		$	8
		Other assets		4			—			4
	Natural gas	Other current assets		—			1			1
		Other assets		1			—			1
	Power	Other current assets		14			—			14
		Other assets		1			—			1
		Total assets	$	28		$	1		$	29
	Derivative liabilities not designated as hedging instruments(a)
	Commodity contracts:
	Fuel oils	MTM derivative liabilities	$	(b)		$	—		$	2
		Other current liabilities		2			—			—
		Other deferred credits and liabilities		2			—			2
	Natural gas	MTM derivative liabilities		(b)			56			64
		Other current liabilities		8			—			—
		Other deferred credits and liabilities		7			38			45
	Power	MTM derivative liabilities		(b)			21			25
		Other current liabilities		4			—			—
		Other deferred credits and liabilities		—			90			90
	Uranium	MTM derivative liabilities		(b)			—			1
		Other current liabilities		1			—			—
		Other deferred credits and liabilities		1			—			1
		Total liabilities	$	25		$	205		$	230
	(a)	Includes derivatives subject to regulatory deferral.
	(b)	Balance sheet line item not applicable to registrant.
Cumulative Pretax Net Gains (Losses) On All Derivative Instruments In OCI	'
	The following table presents the cumulative amount of pretax net gains (losses) on all derivative instruments deferred in regulatory assets or regulatory liabilities as of December 31, 2013, and 2012:
			Ameren			Ameren			Ameren
			Missouri			Illinois
	2013
	Cumulative gains (losses) deferred in regulatory liabilities or assets:
	Fuel oils derivative contracts(a)	$	2		$	—		$	2
	Natural gas derivative contracts(b)		(10	)		(45	)		(55	)
	Power derivative contracts(c)		19			(108	)		(89	)
	Uranium derivative contracts(d)		(6	)		—			(6	)
	2012
	Cumulative gains (losses) deferred in regulatory liabilities or assets:
	Fuel oils derivative contracts(a)	$	4		$	—		$	4
	Natural gas derivative contracts(b)		(14	)		(93	)		(107	)
	Power derivative contracts(c)		12			(111	)		(99	)
	Uranium derivative contracts(d)		(2	)		—			(2	)
	(a)	Represents net gains on fuel oils derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri’s transportation costs for coal through October 2016, as of December 31, 2013. Current gains deferred as regulatory liabilities include $3 million and $3 million at Ameren and Ameren Missouri as of December 31, 2013, respectively. Current losses deferred as regulatory assets include $1 million and $1 million at Ameren and Ameren Missouri as of December 31, 2013, respectively.
	(b)	Represents net losses associated with natural gas derivative contracts. These contracts are a partial hedge of natural gas requirements through October 2019 at Ameren and Ameren Missouri and through March 2017 at Ameren Illinois, in each case as of December 31, 2013. Current gains deferred as regulatory liabilities include $2 million, $1 million, and $1 million at Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2013. Current losses deferred as regulatory assets include $32 million, $5 million, and $27 million at Ameren, Ameren Missouri and Ameren Illinois, respectively, as of December 31, 2013.
	(c)	Represents net gains (losses) associated with power derivative contracts. These contracts are a partial hedge of power price requirements through May 2032 at Ameren and Ameren Illinois and through December 2015 at Ameren Missouri, in each case as of December 31, 2013. Current gains deferred as regulatory liabilities include $23 million and $23 million at Ameren and Ameren Missouri, respectively, as of December 31, 2013. Current losses deferred as regulatory assets include $13 million, $4 million, and $9 million at Ameren, Ameren Missouri and Ameren Illinois, respectively, as of December 31, 2013.
	(d)	Represents net losses on uranium derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri's uranium requirements through October 2016, as of December 31, 2013. Current losses deferred as regulatory assets include $5 million and $5 million at Ameren and Ameren Missouri as of December 31, 2013, respectively.
Derivative Instruments With Credit Risk-Related Contingent Features	'
	The following table presents, as of December 31, 2013, and 2012, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that could be required to be posted with counterparties. The additional collateral required is the net liability position allowed under the master trading and netting agreements assuming (1) the credit risk-related contingent features underlying these agreements were triggered on December 31, 2013, or 2012, respectively, and (2) those counterparties with rights to do so requested collateral:
		Aggregate Fair Value of				Cash				Potential Aggregate Amount of
		Derivative Liabilities(a)				Collateral Posted				Additional Collateral Required(b)
	2013
	Ameren Missouri	$	70			$	2			$	67
	Ameren Illinois	75				15				55
	Ameren	$	145			$	17			$	122
	2012
	Ameren Missouri	$	78			$	3			$	71
	Ameren Illinois	148				58				84
	Ameren	$	226			$	61			$	155
	(a)	Prior to consideration of master trading and netting agreements and including NPNS and accrual contract exposures.
	(b)	As collateral requirements with certain counterparties are based on master trading and netting agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such agreements.
Derivatives That Qualify For Regulatory Deferral	'
	The following table represents the net change in market value associated with derivatives that qualify for regulatory deferral for the years ended December 31, 2013 and 2012:
				Gain (Loss) Recognized
				in Regulatory Liabilities
				or Regulatory Assets
				2013				2012
	Ameren (a)	Fuel oils		$	(2	)		$	(15	)
		Natural gas		52				84
		Power		10				(180		)
		Uranium		(4		)		(1		)
		Total		$	56			$	(112	)
	Ameren Missouri	Fuel oils		$	(2	)		$	(15	)
		Natural gas		4				10
		Power		7				(9		)
		Uranium		(4		)		(1		)
		Total		$	5			$	(15	)
	Ameren Illinois	Natural gas		$	48			$	74
		Power		3				29
		Total		$	51			$	103
	(a)	Amounts include intercompany eliminations.
Offsetting Derivative Assets and Liabilities [Table Text Block]	'
	The following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of December 31, 2013, and 2012:
						Gross Amounts Not Offset in the Balance Sheet
			Gross Amounts Recognized in the Balance Sheet			Derivative Instruments			Cash Collateral Received/Posted(a)			Net
												Amount
	2013
	Commodity contracts eligible to be offset:
	Assets:
	Ameren Missouri	$	33		$	9		$	—		$	24
	Ameren Illinois		1			1			—			—
	Ameren	$	34		$	10		$	—		$	24
	Liabilities:
	Ameren Missouri	$	24		$	9		$	9		$	6
	Ameren Illinois		154			1			15			138
	Ameren	$	178		$	10		$	24		$	144
	2012
	Commodity contracts eligible to be offset:
	Assets:
	Ameren Missouri	$	28		$	9		$	—		$	19
	Ameren Illinois		1			1			—			—
	Ameren	$	29		$	10		$	—		$	19
	Liabilities:
	Ameren Missouri	$	25		$	9		$	7		$	9
	Ameren Illinois		205			1			58			146
	Ameren	$	230		$	10		$	65		$	155
	(a)	Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” and “Other assets” on the balance sheet.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Inputs, Assets and Liabilities, Quantitative Information	'
	The following table describes the valuation techniques and unobservable inputs for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy for the period ended December 31, 2013:
			Fair Value									Weighted
			Assets			Liabilities			Valuation Technique(s)	Unobservable Input	Range	Average
	Level 3 Derivative asset and liability – commodity contracts(a):
	Ameren	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	Oct-35	16
									Discounted cash flow	Counterparty credit risk(%)(c)(d)	0.26 - 2	1
		Power(e)	21			(110		)	Discounted cash flow	Average forward peak and off-peak pricing - forwards/swaps($/MWh)(c)	25 - 51	32
										Estimated auction price for FTRs($/MW)(b)	(1,594) - 945	305
										Nodal basis($/MWh)(c)	(3) - (1)	-2
										Counterparty credit risk(%)(c)(d)	0.39 - 0.50	0.42
										Ameren credit risk(%)(c)(d)	2	(f)
									Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	5-Apr	5
										Escalation rate(%)(b)(g)	4-Mar	4
									Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
		Uranium	—			(6		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	34 - 41	36
	Ameren Missouri	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	Oct-35	16
									Discounted cash flow	Counterparty credit risk(%)(c)(d)	0.26 - 2	1
		Power(e)	21			(2		)	Discounted cash flow	Average forward peak and off-peak pricing - forwards/swaps($/MWh)(c)	25 - 51	40
										Estimated auction price for FTRs($/MW)(b)	(1,594) - 945	305
										Nodal basis($/MWh)(c)	(3) - (1)	-2
										Counterparty credit risk(%)(c)(d)	0.39 - 0.50	0.42
										Ameren Missouri credit risk(%)(c)(d)	2	(f)
		Uranium	—			(6		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	34 - 41	36
	Ameren Illinois	Power(e)	$	—		$	(108	)	Discounted cash flow	Average forward peak and off-peak pricing - forwards/swaps($/MWh)(b)	27 - 36	30
										Nodal basis($/MWh)(b)	(4) - 0	-2
										Ameren Illinois credit risk(%)(c)(d)	2	(f)
									Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	5-Apr	5
										Escalation rate(%)(b)(g)	4-Mar	4
									Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
	(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
	(b)	Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
	(c)	Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
	(d)	Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren, Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
	(e)	Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2017. Valuations beyond 2017 use fundamentally modeled pricing by month for peak and off-peak demand.
	(f)	Not applicable.
	(g)	Escalation rate applies to power prices 2026 and beyond.
	The following table describes the valuation techniques and unobservable inputs for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2012:
			Fair Value									Weighted
			Assets			Liabilities			Valuation Technique	Unobservable Input	Range	Average
	Level 3 Derivative asset and liability – commodity contracts(a):
	Ameren	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	27-Jul	24
									Discounted cash flow	Escalation rate(%)(b)	0.21 - 0.60	0.44
										Counterparty credit risk(%)(c)(d)	0.12 - 1	1
										Ameren credit risk(%)(c)(d)	2	(e)
		Power(f)	14			(114		)	Discounted cash flow	Average forward peak and off-peak power pricing - forwards/swaps($/MWh)(c)	22 - 47	31
										Estimated auction price for FTRs($/MW)(b)	(281) - 1,851	178
										Nodal basis($/MWh)(c)	(5) - (1)	-3
										Counterparty credit risk(%)(c)(d)	0.22 - 1	1
										Ameren credit risk(%)(c)(d)	5-Feb	5
									Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	8-Apr	6
									Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
		Uranium	—			(2		)	Discounted cash flow	Average forward uranium pricing($/pound)(b)	43 - 46	44
	Ameren Missouri	Fuel oils	$	8		$	(3	)	Option model	Volatilities(%)(b)	27-Jul	24
									Discounted cash flow	Escalation rate(%)(b)	0.21 - 0.60	0.44
										Counterparty credit risk(%)(c)(d)	0.12 - 1	1
										Ameren Missouri credit risk(%)(c)(d)	2	(e)
		Power(f)	14			(3		)	Discounted cash flow	Average forward peak and off-peak power pricing - forwards/swaps($/MWh)(c)	24 - 56	36
										Estimated auction price for FTRs($/MW)(b)	(281) - 1,851	178
										Nodal basis($/MWh)(c)	(5) - (1)	-2
										Counterparty credit risk(%)(c)(d)	0.22 - 1	1
										Ameren Missouri credit risk(%)(c)(d)	2	(e)
		Uranium	—			(2		)	Discounted cash flow	Average forward uranium pricing($/pound)(b)	43 - 46	44
	Ameren Illinois	Power(f)	$	—		$	(111	)	Discounted cash flow	Average forward peak and off-peak power pricing - forwards/swaps($/MWh)(b)	22 - 47	30
									Nodal basis($/MWh)(b)	(5) - (1)	-3
									Ameren Illinois credit risk(%)(c)(d)	5	(e)
								Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	8-Apr	6
								Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	7-May	6
(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)	Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
(c)	Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
(d)	Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren, Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
(e)	Not applicable.
(f)	Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2017. Valuations beyond 2017 use fundamentally modeled pricing by month for peak and off-peak demand.
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis	'
	The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2013:
				Quoted Prices in				Significant Other				Significant Other				Total
				Active Markets for				Observable				Unobservable
				Identical Assets				Inputs				Inputs
				or Liabilities				(Level 2)				(Level 3)
				(Level 1)
	Assets:
	Ameren	Derivative assets – commodity contracts(a):
		Fuel oils		$	1			$	—			$	8			$	9
		Natural gas		—				2				—				2
		Power		—				2				21				23
		Total derivative assets – commodity contracts		$	1			$	4			$	29			$	34
		Nuclear decommissioning trust fund:
		Cash and cash equivalents		$	3			$	—			$	—			$	3
		Equity securities:
		U.S. large capitalization		332				—				—				332
		Debt securities:
		Corporate bonds		—				52				—				52
		Municipal bonds		—				2				—				2
		U.S. treasury and agency securities		—				94				—				94
		Asset-backed securities		—				10				—				10
		Other		—				1				—				1
		Total nuclear decommissioning trust fund		$	335			$	159			$	—			$	494
		Total Ameren		$	336			$	163			$	29			$	528
	Ameren Missouri	Derivative assets – commodity contracts(a):
		Fuel oils		$	1			$	—			$	8			$	9
		Natural gas		—				1				—				1
		Power		—				2				21				23
		Total derivative assets – commodity contracts		$	1			$	3			$	29			$	33
		Nuclear decommissioning trust fund:
		Cash and cash equivalents		$	3			$	—			$	—			$	3
		Equity securities:
		U.S. large capitalization		332				—				—				332
		Debt securities:
		Corporate bonds		—				52				—				52
		Municipal bonds		—				2				—				2
		U.S. treasury and agency securities		—				94				—				94
		Asset-backed securities		—				10				—				10
		Other		—				1				—				1
		Total nuclear decommissioning trust fund		$	335			$	159			$	—			$	494
		Total Ameren Missouri		$	336			$	162			$	29			$	527
	Ameren Illinois	Derivative assets – commodity contracts(a):
		Natural gas		$	—			$	1			$	—			$	1
	Liabilities:
	Ameren	Derivative liabilities – commodity contracts(a):
		Fuel oils		$	—			$	—			$	3			$	3
		Natural gas		3				54				—				57
		Power		—				2				110				112
		Uranium		—				—				6				6
		Total Ameren		$	3			$	56			$	119			$	178
	Ameren Missouri	Derivative liabilities – commodity contracts(a):
		Fuel oils		$	—			$	—			$	3			$	3
		Natural gas		3				8				—				11
		Power		—				2				2				4
		Uranium		—				—				6				6
		Total Ameren Missouri		$	3			$	10			$	11			$	24
	Ameren Illinois	Derivative liabilities – commodity contracts(a):
		Natural gas		$	—			$	46			$	—			$	46
		Power		—				—				108				108
		Total Ameren Illinois		$	—			$	46			$	108			$	154
	(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
	The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2012:
				Quoted Prices in				Significant Other				Significant				Total
Active Markets for				Observable Inputs				Other
Identical Assets				(Level 2)				Unobservable
or Liabilities								Inputs
(Level 1)								(Level 3)
Assets:
Ameren	Derivative assets – commodity contracts(a):
	Fuel oils		$	4			$	—			$	8			$	12
	Natural gas		—				2				—				2
	Power		—				1				14				15
	Total derivative assets – commodity contracts		$	4			$	3			$	22			$	29
	Nuclear decommissioning trust fund:
	Cash and cash equivalents		$	1			$	—			$	—			$	1
	Equity securities:
	U.S. large capitalization		264				—				—				264
	Debt securities:
	Corporate bonds		—				47				—				47
	Municipal bonds		—				1				—				1
	U.S. treasury and agency securities		—				81				—				81
	Asset-backed securities		—				11				—				11
	Other		—				1				—				1
	Total nuclear decommissioning trust fund		$	265			$	141			$	—			$	406	(b)
	Total Ameren		$	269			$	144			$	22			$	435
Ameren Missouri	Derivative assets – commodity contracts(a):
	Fuel oils		$	4			$	—			$	8			$	12
	Natural gas		—				1				—				1
	Power		—				1				14				15
	Total derivative assets – commodity contracts		$	4			$	2			$	22			$	28
	Nuclear decommissioning trust fund:
	Cash and cash equivalents		$	1			$	—			$	—			$	1
	Equity securities:
	U.S. large capitalization		264				—				—				264
	Debt securities:
	Corporate bonds		—				47				—				47
	Municipal bonds		—				1				—				1
	U.S. treasury and agency securities		—				81				—				81
	Asset-backed securities		—				11				—				11
	Other		—				1				—				1
	Total nuclear decommissioning trust fund		$	265			$	141			$	—			$	406	(b)
	Total Ameren Missouri		$	269			$	143			$	22			$	434
Ameren Illinois	Derivative assets – commodity contracts(a):
	Natural gas		$	—			$	1			$	—			$	1
Liabilities:
Ameren	Derivative liabilities – commodity contracts(a):
	Fuel oils		$	1			$	—			$	3			$	4
	Natural gas		7				102				—				109
	Power		—				1				114				115
	Uranium		—				—				2				2
	Total Ameren		$	8			$	103			$	119			$	230
Ameren Missouri	Derivative liabilities – commodity contracts(a):
	Fuel oils		$	1			$	—			$	3			$	4
	Natural gas		7				8				—				15
	Power		—				1				3				4
	Uranium		—				—				2				2
	Total Ameren Missouri		$	8			$	9			$	8			$	25
Ameren Illinois	Derivative liabilities – commodity contracts(a):
	Natural gas		$	—			$	94			$	—			$	94
	Power		—				—				111				111
	Total Ameren Illinois		$	—			$	94			$	111			$	205
(a)	The derivative asset and liability balances are presented net of counterparty credit considerations.
(b)	Balance excludes $2 million of receivables, payables, and accrued income, net.
Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy	'
	The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2013:
			Net Derivative Commodity Contracts
			Ameren			Ameren			Ameren
			Missouri			Illinois
	Fuel oils:
	Beginning balance at January 1, 2013	$	5		$	(a)		$	5
	Realized and unrealized gains (losses):
	Included in regulatory assets/liabilities		—			(a)			—
	Total realized and unrealized gains (losses)		—			(a)			—
	Purchases		3			(a)			3
	Sales		(1	)		(a)			(1	)
	Settlements		(2	)		(a)			(2	)
	Ending balance at December 31, 2013	$	5		$	(a)		$	5
	Change in unrealized gains (losses) related to assets/liabilities held at December 31,2013	$	—		$	(a)		$	—
	Natural gas:
	Beginning balance at January 1, 2013	$	—		$	—		$	—
	Realized and unrealized gains (losses):
	Included in regulatory assets/liabilities		—			(1	)		(1	)
	Total realized and unrealized gains (losses)		—			(1	)		(1	)
	Purchases		—			1			1
	Ending balance at December 31, 2013	$	—		$	—		$	—
	Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2013	$	—		$	—		$	—
	Power:
	Beginning balance at January 1, 2013	$	11		$	(111	)	$	(100	)
	Realized and unrealized gains (losses):
	Included in regulatory assets/liabilities		3			(18	)		(15	)
	Total realized and unrealized gains (losses)		3			(18	)		(15	)
	Purchases		40			—			40
	Settlements		(36	)		21			(15	)
	Transfers into Level 3		(3	)		—			(3	)
	Transfers out of Level 3		4			—			4
	Ending balance at December 31, 2013	$	19		$	(108	)	$	(89	)
	Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2013	$	(1	)	$	(24	)	$	(25	)
	Uranium:
	Beginning balance at January 1, 2013	$	(2	)	$	(a)		$	(2	)
	Realized and unrealized gains (losses):
	Included in regulatory assets/liabilities		(3	)		(a)			(3	)
	Total realized and unrealized gains (losses)		(3	)		(a)			(3	)
	Purchases		(2	)		(a)			(2	)
	Settlements		1			(a)			1
	Ending balance at December 31, 2013	$	(6	)	$	(a)		$	(6	)
	Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2013	$	(2	)	$	(a)		$	(2	)
	(a)	Not applicable.
	The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2012:
			Net Derivative Commodity Contracts
			Ameren			Ameren			Ameren
			Missouri			Illinois
	Fuel oils:
	Beginning balance at January 1, 2012	$	3		$	(a)		$	3
	Realized and unrealized gains (losses):
	Included in regulatory assets/liabilities		(1	)		(a)			(1	)
	Total realized and unrealized gains (losses)		(1	)		(a)			(1	)
	Purchases		7			(a)			7
	Sales		(3	)		(a)			(3	)
	Settlements		(2	)		(a)			(2	)
	Transfers into Level 3		1			(a)			1
	Ending balance at December 31, 2012	$	5		$	(a)		$	5
	Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	(1	)	$	(a)		$	(1	)
	Natural gas:
	Beginning balance at January 1, 2012	$	(14	)	$	(160	)	$	(174	)
	Realized and unrealized gains (losses):
	Included in regulatory assets/liabilities		(2	)		(25	)		(27	)
	Total realized and unrealized gains (losses)		(2	)		(25	)		(27	)
Settlements		1			15			16
Transfers out of Level 3		15			170			185
Ending balance at December 31, 2012	$	—		$	—		$	—
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	—		$	—		$	—
Power(b):
Beginning balance at January 1, 2012	$	21		$	(140	)	$	81
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		11			(226	)		(175	)
Total realized and unrealized gains (losses)		11			(226	)		(175	)
Purchases		21			—			21
Sales		(1	)		—			(1	)
Settlements		(37	)		255			(22	)
Transfers out of Level 3		(4	)		—			(4	)
Ending balance at December 31, 2012	$	11		$	(111	)	$	(100	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	—		$	(191	)	(c) $	(175	)
Uranium:
Beginning balance at January 1, 2012	$	(1	)	$	(a)		$	(1	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(2	)		(a)			(2	)
Total realized and unrealized gains (losses)		(2	)		(a)			(2	)
Settlements		1			(a)			1
Ending balance at December 31, 2012	$	(2	)	$	(a)		$	(2	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	(1	)	$	(a)		$	(1	)
(a)	Not applicable.
(b)	Ameren amounts include intercompany eliminations.
(c)	The change in unrealized losses was due to decreases in long-term power prices applied to 20-year Ameren Illinois swap contracts, which expire in May 2032.
Schedule Of Transfers Between Fair Value Hierarchy Levels	'
	The following table summarizes all transfers between fair value hierarchy levels related to derivative commodity contracts for the years ended December 31, 2013 and 2012:
		2013				2012
	Ameren - derivative commodity contracts:
	Transfers into Level 3 / Transfers out of Level 1 – Fuel oils	$	—			$	1
	Transfers out of Level 3 / Transfers into Level 2 – Natural gas	—				185
	Transfers into Level 3 / Transfers out of Level 2 – Power	(3		)		—
	Transfers out of Level 3 / Transfers into Level 2 – Power	4				(4		)
	Net fair value of Level 3 transfers	$	1			$	182
	Ameren Missouri - derivative commodity contracts:
	Transfers into Level 3 / Transfers out of Level 1 – Fuel oils	$	—			$	1
	Transfers out of Level 3 / Transfers into Level 2 – Natural gas	—				15
	Transfers into Level 3 / Transfers out of Level 2 – Power	(3		)		—
	Transfers out of Level 3 / Transfers into Level 2 – Power	4				(4		)
	Net fair value of Level 3 transfers	$	1			$	12
	Ameren Illinois - derivative commodity contracts:
	Transfers out of Level 3 / Transfers into Level 2 – Natural gas	$	—			$	170
Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock	'
	The following table presents the carrying amounts and estimated fair values of our long-term debt and preferred stock at December 31, 2013 and 2012:
		2013								2012
		Carrying Amount				Fair Value				Carrying Amount				Fair Value
	Ameren:(a)
	Long-term debt and capital lease obligations (including current portion)	$	6,038			$	6,584			$	6,157			$	7,110
	Preferred stock	142				118				142				123
	Ameren Missouri:
	Long-term debt and capital lease obligations (including current portion)	$	3,757			$	4,124			$	4,006			$	4,625
	Preferred stock	80				71				80				74
	Ameren Illinois:
	Long-term debt (including current portion)	$	1,856			$	2,028			$	1,727			$	2,020
	Preferred stock	62				47				62				49
	(a)	Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.

Nuclear_Decommissioning_Trust_1

Nuclear Decommissioning Trust Fund Investments (Tables)	12 Months Ended
	Dec. 31, 2013
Nuclear Decommissioning Trust Fund Investments [Line Items]	'
Fair Value Of Securities In Nuclear Decommissioning Trust Fund	'
	The following table presents the costs and fair values of investments in debt and equity securities in Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2013, and 2012:
	Security Type	Cost		Gross Unrealized Gain			Gross Unrealized Loss		Fair Value
	2013
	Debt securities	$	157	$	4	$	2		$	159
	Equity securities	137		199			4		332
	Cash	3		—			—		3
	Other(b)	(a)		—			—		(a)
	Total	$	297	$	203	$	6		$	494
	2012
	Debt securities	$	133	$	8	$	(a)		$	141
	Equity securities	145		130			11		264
	Cash	1		—			—		1
	Other(b)	2		—			—		2
	Total	$	281	$	138	$	11		$	408
	(a)	Amount less than $1 million.
	(b)	Represents payables relating to pending security purchases, net of receivables related to pending security sales and interest receivables.
Schedule Of Unrealized Losses On Available-For-Sale Investments Included In Nuclear Decommissioning Trust Fund	'
	They are aggregated by investment category and the length of time that individual securities have been in a continuous unrealized loss position at December 31, 2013:
		Less than 12 Months						12 Months or Greater			Total
		Fair Value		Gross				Fair Value		Gross	Fair Value		Gross
				Unrealized						Unrealized			Unrealized
				Losses						Losses			Losses
	Debt securities	$	72	$	2		$	(a)	$	(a)	$	72	$	2
	Equity securities	6		(a)				7		4	13		4
	Total	$	78	$	2		$	7	$	4	$	85	$	6
	(a)	Amount less than $1 million.
Regulatory Asset	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'
Proceeds From Sale Of Investments In Nuclear Decommissioning Trust Fund And Gross Realized Gains And Losses	'
	The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2013, 2012, and 2011:
		2013		2012			2011
	Proceeds from sales and maturities	$	196	$	384		$	199
	Gross realized gains	7		6			5
	Gross realized losses	5		2			4
Fair Value Of Securities In Nuclear Decommissioning Trust Fund According To Their Contractual Maturities	'
	The following table presents the costs and fair values of investments in debt securities in Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2013:
		Cost		Fair Value
	Less than 5 years	$	93	$	94
	5 years to 10 years	31		32
	Due after 10 years	33		33
	Total	$	157	$	159

Retirement_Benefits_Tables

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2013
Summary Of Benefit Liability Recorded	'
	The following table presents the net benefit liability recorded on the balance sheets of each of the Ameren Companies as of December 31, 2013, and 2012:
		2013			2012
	Ameren(a)	$	461		$	1,143
	Ameren Missouri	191			464
	Ameren Illinois	198			408
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI	'
	The following table presents the funded status of our pension and postretirement benefit plans as of December 31, 2013, and 2012. It also provides the amounts included in regulatory assets and accumulated OCI at December 31, 2013, and 2012, that have not been recognized in net periodic benefit costs.
		2013							2012
		Pension Benefits(a)				Postretirement			Pension Benefits(a)				Postretirement
						Benefits(a)							Benefits(a)
	Accumulated benefit obligation at end of year	$	3,698		$	(b)			$	3,829		$	(b)
	Change in benefit obligation:
	Net benefit obligation at beginning of year	$	4,051		$	1,157			$	3,764		$	1,145
	Service cost	91				22			81				22
	Interest cost	163				46			166				47
	Participant contributions	—				16			—				16
	Actuarial (gain) loss	(207		)		(76	)		240				(10	)
	Curtailment gain(c)	—				(3	)		—				—
	Settlement(d)	—				(5	)		—				—
	Benefits paid	(198		)		(64	)		(200		)		(69	)
	Early retiree reinsurance program receipt	(b)				—			(b)				2
	Federal subsidy on benefits paid	(b)				3			(b)				4
	Net benefit obligation at end of year	3,900				1,096			4,051				1,157
	Change in plan assets:
	Fair value of plan assets at beginning of year	3,127				938			2,814				836
	Actual return on plan assets	376				156			385				104
	Employer contributions	156				25			128				45
	Federal subsidy on benefits paid	(b)				3			(b)				4
	Early retiree reinsurance program receipt	(b)				—			(b)				2
	Participant contributions	—				16			—				16
	Benefits paid	(198		)		(64	)		(200		)		(69	)
	Fair value of plan assets at end of year	3,461				1,074			3,127				938
	Funded status – deficiency	439				22			924				219
	Accrued benefit cost at December 31	$	439		$	22			$	924		$	219
	Amounts recognized in the balance sheet consist of:
	Noncurrent asset(e)	$	—		$	(9	)		$	—		$	—
	Current liability(f)	3				1			3				2
	Noncurrent liability	436				30			921				217
	Net liability recognized	$	439		$	22			$	924		$	219
	Amounts recognized in regulatory assets consist of:
	Net actuarial (gain) loss	$	282		$	(71	)		$	699		$	103
	Prior service cost (credit)	(7		)		(20	)		(6		)		(24	)
	Amounts (pretax) recognized in accumulated OCI consist of:
	Net actuarial (gain) loss	17				(12	)		65				5
	Prior service cost (credit)	—				(1	)		(14		)		(6	)
	Total	$	292		$	(104	)		$	744		$	78
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
	(b)	Not applicable.
Assumptions Used To Determine Benefit Obligations	'
	The following table presents the assumptions used to determine our benefit obligations at December 31, 2013, and 2012:
		Pension Benefits						Postretirement Benefits
		2013			2012			2013			2012
	Discount rate at measurement date	4.75	%		4	%		4.75	%		4	%
	Increase in future compensation	3.5			3.5			3.5			3.5
	Medical cost trend rate (initial)	—			—			5			5
	Medical cost trend rate (ultimate)	—			—			5			5
	Years to ultimate rate	—			—			—			—
Schedule Of Cash Contributions Made To Benefit Plans	'
	The following table presents the cash contributions made to our defined benefit retirement plan and to our postretirement plans during 2013, 2012, and 2011:
		Pension Benefits												Postretirement Benefits
		2013				2012				2011				2013				2012		2011
	Ameren Missouri	$	60			$	52			$	43			$	10			$	9	$	9
	Ameren Illinois	50				46				28				11				35		118
	Other	46				30				25				4				1		2
	Ameren(a)	156				128				96				25				45		129
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Target Allocation Of The Plans' Asset Categories	'
	The following table presents our target allocations for 2014 and our pension and postretirement plans’ asset categories as of December 31, 2013, and 2012.
	Asset	Target Allocation		Percentage of Plan Assets at December  31,
	Category	2014		2013			2012
	Pension Plan:
	Cash and cash equivalents	0 - 5  %		2	%		2	%
	Equity securities:
	U.S. large capitalization	29 - 39		36			34	%
	U.S. small and mid-capitalization	2 - 12		8			7	%
	International and emerging markets	9 - 19		14			13	%
	Total equity	50 - 60		58			54	%
	Debt securities	35 - 45		36			39	%
	Real estate	0 -   9		4			4	%
	Private equity	0 -   4		(a)			1	%
	Total			100	%		100	%
	Postretirement Plans:
	Cash and cash equivalents	0 - 10 %		4	%		4	%
	Equity securities:
	U.S. large capitalization	33 - 43		41	%		40	%
	U.S. small and mid-capitalization	3 - 13		8	%		8	%
	International	10 - 20		14	%		14	%
	Total equity	55 - 65		63	%		62	%
	Debt securities	30 - 40		33	%		34	%
	Total			100	%		100	%
Changes In The Fair Value Of Plan Assets Classified As Level 3	'
	The following table summarizes the changes in the fair value of the pension plan assets classified as Level 3 in the fair value hierarchy for each of the years ended December 31, 2013, and 2012:
		Beginning				Actual Return on				Actual Return on				Purchases,				Net		Ending Balance at
		Balance at				Plan Assets Related				Plan Assets Related				Sales, and				Transfers		December 31,
		January 1,				to Assets Still Held				to Assets Sold				Settlements, Net				into (out of)
						at the Reporting Date				During the Period								of Level 3
	2013:00:00
	Real estate	$	118			$	9			$	—			$	4			$	—	$	131
	Private equity	19				(9		)		11				(6		)		—		15
	2012:00:00
	Real estate	$	108			$	7			$	—			$	3			$	—	$	118
	Private equity	23				(7		)		8				(5		)		—		19
Components Of Net Periodic Benefit Cost	'
	The following table presents the components of the net periodic benefit cost of our pension and postretirement benefit plans during 2013, 2012, and 2011:
		Pension Benefits				Postretirement Benefits
		Ameren(a)				Ameren(a)
	2013
	Service cost	$	91			$	22
	Interest cost	163				46
	Expected return on plan assets	(218		)		(62		)
	Amortization of:
	Transition obligation	—				—
	Prior service cost	(2		)		(6		)
	Actuarial loss	87				8
	Curtailment gain	(12		)		(7		)
	Net periodic benefit cost(b)	$	109			$	1
	2012
	Service cost	$	81			$	22
	Interest cost	166				47
	Expected return on plan assets	(208		)		(56		)
	Amortization of:
	Transition obligation	—				2
	Prior service cost	(3		)		(6		)
	Actuarial loss	75				5
	Net periodic benefit cost(c)	$	111			$	14
	2011
	Service cost	$	73			$	20
	Interest cost	175				54
	Expected return on plan assets	(211		)		(50		)
	Amortization of:
	Transition obligation	—				2
	Prior service cost	(1		)		(6		)
	Actuarial loss	41				3
	Net periodic benefit cost(c)	$	77			$	23
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Summary Of Estimated Amortizable Amounts From Regulatory Assets and Accumulated OCI Into Net Periodic Benefit Cost	'
	The estimated amounts that will be amortized from regulatory assets and accumulated OCI into net periodic benefit cost in 2014 are as follows:
		Pension Benefits				Postretirement Benefits
		Ameren(a)				Ameren(a)
	Regulatory assets:
	Prior service cost (credit)	$	(1	)		$	(4	)
	Net actuarial loss	60				9
	Accumulated OCI:
	Net actuarial (gain) loss	1				(2		)
	Total	$	60			$	3
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Summary Of Benefit Plan Costs Incurred	'
	The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred and included in continuing operations for the years ended December 31, 2013, 2012, and 2011:
		Pension Costs												Postretirement Costs
		2013				2012				2011				2013				2012		2011
	Ameren Missouri	$	69			$	63			$	51			$	8			$	10	$	11
	Ameren Illinois	41				37				16				—				4		11
	Other	5				2				3				—				—		1
	Ameren(a)	115				102				70				8				14		23
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Schedule Of Expected Payments From Qualified Trust And Company Funds	'
	The expected pension and postretirement benefit payments from qualified trust and company funds and the federal subsidy for postretirement benefits related to prescription drug benefits, which reflect expected future service, as of December 31, 2013, are as follows:
		Pension Benefits								Postretirement Benefits
		Paid from				Paid from				Paid from				Paid from				Federal
		Qualified				Company				Qualified				Company				Subsidy
		Trust				Funds				Trust				Funds
	2014	$	247			$	3			$	61			$	2			$	3
	2015	249				3				63				2				4
	2016	255				3				66				2				4
	2017	260				3				69				2				4
	2018	264				3				72				2				4
	2019 - 2023	1,342				14				394				12				19
Assumptions Used To Determine Net Periodic Benefit Cost	'
	The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2013, 2012, and 2011:
		Pension Benefits									Postretirement Benefits
		2013			2012			2011			2013			2012			2011
	Discount rate at measurement date	4	%		4.5	%		5.25	%		4	%		4.5	%		5.25	%
	Expected return on plan assets	7.5			7.75			8			7.25			7.5			7.75
	Increase in future compensation	3.5			3.5			3.5			3.5			3.5			3.5
	Medical cost trend rate (initial)	—			—			—			5			5.5			6
	Medical cost trend rate (ultimate)	—			—			—			5			5			5
	Years to ultimate rate	—			—			—			—			1 year			2 years
Schedule Of Potential Changes In Key Assumptions	'
	The table below reflects the sensitivity of Ameren’s plans to potential changes in key assumptions:
		Pension Benefits								Postretirement Benefits
		Service Cost				Projected				Service Cost				Postretirement
		and Interest				Benefit				and Interest				Benefit
		Cost				Obligation				Cost				Obligation
	0.25% decrease in discount rate	$	(2	)		$	109			$	—			$	32
	0.25% increase in salary scale	2				17				—				—
	1.00% increase in annual medical trend	—				—				2				40
	1.00% decrease in annual medical trend	—				—				(2		)		(37		)
Schedule Of Matching Contributions	'
	The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to the continuing operations for each of the Ameren Companies for the years ended December 31, 2013, 2012, and 2011:
		2013				2012				2011
	Ameren Missouri	$	16			$	16			$	16
	Ameren Illinois	10				9				8
	Other	1				1				1
	Ameren(a)	27				26				25
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
Pension Benefits	'
Target Allocation Of The Plans' Asset Categories	'
	The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2013:
		Quoted Prices in				Significant Other				Significant Other				Total
		Active Markets for				Observable Inputs				Unobservable
		Identified Assets				(Level 2)				Inputs
		(Level 1)								(Level 3)
	Cash and cash equivalents	$	5			$	39			$	—			$	44
	Equity securities:
	U.S. large capitalization	107				1,162				—				1,269
	U.S. small and mid-capitalization	273				—				—				273
	International and emerging markets	143				372				—				515
	Debt securities:
	Corporate bonds	—				860				—				860
	Municipal bonds	—				149				—				149
	U.S. treasury and agency securities	—				256				—				256
	Other	—				27				—				27
	Real estate	—				—				131				131
	Private equity	—				—				15				15
	Derivative assets	1				—				—				1
	Derivative liabilities	(1		)		—				—				(1		)
	Total	$	528			$	2,865			$	146			$	3,539
	Less: Medical benefit assets at December 31(a)													(112		)
	Plus: Net receivables at December 31(b)													34
	Fair value of pension plans assets at year end													$	3,461
	(a)	Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
	(b)	Receivables related to pending security sales, offset by payables related to pending security purchases.
	The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plan assets measured at fair value as of December 31, 2012:
		Quoted Prices in				Significant Other				Significant Other				Total
		Active Markets for				Observable Inputs				Unobservable
		Identified Assets				(Level 2)				Inputs
		(Level 1)								(Level 3)
	Cash and cash equivalents	$	1			$	28			$	—			$	29
	Equity securities:
	U.S. large capitalization	83				1,007				—				1,090
	U.S. small and mid-capitalization	235				—				—				235
	International and emerging markets	134				301				—				435
	Debt securities:
	Corporate bonds	—				832				—				832
	Municipal bonds	—				176				—				176
	U.S. treasury and agency securities	—				250				—				250
	Other	—				17				—				17
	Real estate	—				—				118				118
	Private equity	—				—				19				19
	Derivative assets	—				—				—				—
	Derivative liabilities	(1		)		—				—				(1		)
	Total	$	452			$	2,611			$	137			$	3,200
	Less: Medical benefit assets at December 31(a)													(102		)
	Plus: Net receivables at December 31(b)													29
	Fair value of pension plans assets at year end													$	3,127
	(a)	Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
	(b)	Receivables related to pending security sales, offset by payables related to pending security purchases.
Postretirement Benefits	'
Target Allocation Of The Plans' Asset Categories	'
	The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2013:
		Quoted Prices in				Significant Other				Significant Other				Total
		Active Markets for				Observable Inputs				Unobservable
		Identified Assets				(Level 2)				Inputs
		(Level 1)								(Level 3)
	Cash and cash equivalents	$	77			$	—			$	—			$	77
	Equity securities:
	U.S. large capitalization	297				101				—				398
	U.S. small and mid-capitalization	77				—				—				77
	International	39				96				—				135
	Debt securities:
	Corporate bonds	—				89				—				89
	Municipal bonds	—				103				—				103
	U.S. treasury and agency securities	—				72				—				72
	Asset-backed securities	—				10				—				10
	Other	—				40				—				40
	Total	$	490			$	511			$	—			$	1,001
	Plus: Medical benefit assets at December 31(a)													112
	Less: Net payables at December 31(b)													(39		)
	Fair value of postretirement benefit plans assets at year end													$	1,074
	(a)	Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
	(b)	Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.
	The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans assets measured at fair value as of December 31, 2012:
		Quoted Prices in				Significant Other				Significant Other				Total
		Active Markets for				Observable Inputs				Unobservable
		Identified Assets				(Level 2)				Inputs
		(Level 1)								(Level 3)
	Cash and cash equivalents	$	83			$	—			$	—			$	83
	Equity securities:
	U.S. large capitalization	245				88				—				333
	U.S. small and mid-capitalization	66				—				—				66
	International	45				69				—				114
	Debt securities:
	Corporate bonds	—				88				—				88
	Municipal bonds	—				91				—				91
	U.S. treasury and agency securities	—				67				—				67
	Asset-backed securities	—				18				—				18
	Other	—				22				—				22
	Total	$	439			$	443			$	—			$	882
	Plus: Medical benefit assets at December 31(a)													102
	Less: Net payables at December 31(b)													(46		)
	Fair value of postretirement benefit plans assets at year end													$	938
	(a)	Medical benefit (health and welfare) component for 401(h) accounts to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
	(b)	Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Summary Of Nonvested Shares Related To Long-Term Incentive Plan	'
	A summary of nonvested shares at December 31, 2013, and changes during the year ended December 31, 2013, under the 2006 Plan are presented below:
		Performance Share Units
		Share		Weighted-average
		Units		Fair Value per Unit
	Nonvested at January 1, 2013	1,192,487		$	33.56
	Granted(a)	840,482		31.19
	Unearned or forfeited(b)	(29,730	)	31.93
	Earned and vested(c)	(784,695	)	31.6
	Nonvested at December 31, 2013	1,218,544		$	33.23
	(a)	Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2013 under the 2006 Plan.
	(b)	Includes share units granted in 2011 that were not earned based on performance provisions of the award grants.
	(c)	Includes share units granted in 2011 that vested as of December 31, 2013, that were earned pursuant to the provisions of the award grants. Also includes share units that vested due to attainment of retirement eligibility by certain employees and certain employees whose employment terminated on December 2, 2013, with the divestiture of New AER. Actual shares issued for retirement-eligible employees and former New AER subsidiaries' employees will vary depending on actual performance over the three-year measurement period.

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013																Dec. 31, 2012
Income Tax Disclosure [Abstract]	'																'
Schedule Of Effective Income Tax Rate Reconciliation	'																'
	The following table presents the principal reasons why the effective income tax rate differed from the statutory federal income tax rate for the years ended December 31, 2013, 2012, and 2011:
		Ameren Missouri			Ameren Illinois			Ameren
	2013
	Statutory federal income tax rate:	35	%		35	%		35	%
	Increases (decreases) from:
	Depreciation differences	—			(1	)		—
	Amortization of investment tax credit	(1	)		—			(1	)
	State tax	3			6			4
	Other permanent items(a)	1			—			—
	Effective income tax rate	38	%		40	%		38	%
	2012
	Statutory federal income tax rate:	35	%		35	%		35	%
	Increases (decreases) from:
	Depreciation differences	(1	)		—			(1	)
	Amortization of investment tax credit	(1	)		(1	)		(1	)
	State tax	3			6			5
	Reserve for uncertain tax positions	1			—			—
	Other permanent items(a)	—			—			(1	)
	Effective income tax rate	37	%		40	%		37	%
	2011
	Statutory federal income tax rate:	35	%		35	%		35	%
	Increases (decreases) from:
	Depreciation differences	(2	)		—			(1	)
	Amortization of investment tax credit	(1	)		(1	)		(1	)
	State tax	3			5			4
	Reserve for uncertain tax positions	—			—			1
	Tax credits	—			—			(1	)
	Other permanent items(a)	1			—			—
	Effective income tax rate	36	%		39	%		37	%
	(a)	Permanent items are treated differently for book and tax purposes and primarily include non-taxable income related to company-owned life insurance and deductions related to dividends on DRPlus and the 401(k) plan for Ameren, as well as nondeductible expenses related to lobbying and stock issuance costs for Ameren Missouri.
Schedule Of Components Of Income Tax Expense (Benefit)	'																'
	The following table presents the components of income tax expense (benefit) for the years ended December 31, 2013, 2012, and 2011:
		Ameren Missouri				Ameren Illinois				Other				Ameren(a)
	2013
	Current taxes:
	Federal	$	136			$	(15	)		$	(239	)	(b)	$	(118	)
	State	41				21				(43		)	(b)	19
	Deferred taxes:
	Federal	64				99				205			(b)	368
	State	6				6				36			(b)	48
	Deferred investment tax credits, amortization	(5		)		(1		)		—				(6		)
	Total income tax expense (benefit)	$	242			$	110			$	(41	)		$	311
	2012
	Current taxes:
	Federal	$	(25	)		$	(7	)		$	72			$	40
	State	(10		)		(3		)		23				10
	Deferred taxes:
	Federal	248				76				(120		)		204
	State	44				30				(14		)		60
	Deferred investment tax credits, amortization	(5		)		(2		)		—				(7		)
	Total income tax expense (benefit)	$	252			$	94			$	(39	)		$	307
	2011
	Current taxes:
	Federal	$	3			$	(24	)		$	15			$	(6	)
	State	2				(4		)		—				(2		)
	Deferred taxes:
	Federal	129				123				(39		)		213
	State	31				34				(10		)		55
	Deferred investment tax credits, amortization	(4		)		(2		)		—				(6		)
	Total income tax expense (benefit)	$	161			$	127			$	(34	)		$	254
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	These amounts are substantially related to the reversal of unrecognized tax benefits as a result of new IRS guidance related to the deductibility of expenditures to maintain, replace or improve steam or electric power generation property, along with casualty loss deductions for storm damage. They also reflect the increase in deferred tax expense due to available net operating losses.
Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences	'																'
	The following table presents the deferred tax assets and deferred tax liabilities recorded as a result of temporary differences at December 31, 2013, and 2012:
		Ameren Missouri				Ameren Illinois				Other				Ameren(a)
	2013
	Accumulated deferred income taxes, net liability (asset):
	Plant related	$	2,513			$	1,243			$	13			$	3,769
	Regulatory assets, net	74				2				—				76
	Deferred employee benefit costs	(74		)		(85		)		(114		)		(273		)
	Purchase accounting	—				(27		)		(1		)		(28		)
	ARO	(7		)		1				—				(6		)
	Other(b)(c)	(17		)		(63		)		(398		)		(478		)
	Total net accumulated deferred income tax liabilities (assets)(d)	$	2,489			$	1,071			$	(500	)		$	3,060
	2012
	Accumulated deferred income taxes, net liability (asset):
	Plant related	$	2,385			$	1,145			$	20			$	3,550
	Regulatory assets, net	73				—				—				73
	Deferred employee benefit costs	(84		)		(102		)		(137		)		(323		)
	Purchase accounting	—				(27		)		(1		)		(28		)
	ARO	(7		)		1				—				(6		)
	Other(b)	50				(77		)		(223		)		(250		)
	Total net accumulated deferred income tax liabilities (assets)(e)	$	2,417			$	940			$	(341	)		$	3,016
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	Includes deferred tax assets related to net operating loss and tax credit carryforwards detailed in the table below.
	(c)	Includes total valuation allowances for Ameren, Ameren Missouri, and Ameren Illinois of $7 million, $1 million, and $1 million, respectively, as of December 31, 2013. The state valuation allowances are shown in the table below.
	(d)	Includes $20 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2013.
	(e)	Includes $26 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2012.
Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards	'																'
	The following table presents the components of deferred tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2013:																The following table presents the components of deferred tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2012:
		Ameren Missouri				Ameren Illinois				Other				Ameren(a)				Ameren Missouri			Ameren Illinois			Other		Ameren(a)
	Net operating loss carryforwards:																Net operating loss carryforwards:
	Federal(b)	$	61			$	84			$	215			$	360		Federal(b)	$	61		$	61		$	51	$	173
	State(c)	3				11				34				48			State(c)	3			11			13		27
	Total net operating loss carryforwards	$	64			$	95			$	249			$	408		Total net operating loss carryforwards	$	64		$	72		$	64	$	200
	Tax credit carryforwards:																Tax credit carryforwards:
	Federal(d)	$	12			$	—			$	76			$	88		Federal(d)	$	11		$	—		$	75	$	86
	State(e)	1				1				32				34			State(e)	1			1			23		25
	State valuation allowance(f)	(1		)		(1		)		(2		)		(4		)	State valuation allowance(f)	(1		)	(1		)	—		(2		)
	Total tax credit carryforwards	$	12			$	—			$	106			$	118
																	Total tax credit carryforwards	$	11		$	—		$	98	$	109
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
																	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
	(b)	These will begin to expire in 2028.
																	(b)	These will begin to expire in 2028
	(c)	These will begin to expire in 2017.
																	(c)	These will begin to expire in2017.
	(d)	These will begin to expire in 2029.
																	(d)	These will begin to expire in 2029.
	(e)	These will begin to expire in 2014.
																	(e)	These began to expire in 2013.
	(f)	This balance increased by $2 million, $- million and $- million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2013.
																	(f)	This balance increased by $1 million, $- million and $1 million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2012.
Schedule Of Changes To Unrecognized Tax Benefits And Related Interest	'																'
	A reconciliation of the change in the unrecognized tax benefit balance during the years ended December 31, 2011, 2012, and 2013, is as follows:
		Ameren Missouri				Ameren Illinois				Other				Ameren(a)
	Unrecognized tax benefits – January 1, 2011	$	164			$	56			$	26			$	246
	Increases based on tax positions prior to 2011	15				—				7				22
	Decreases based on tax positions prior to 2011	(63		)		(41		)		(21		)		(125		)
	Increases based on tax positions related to 2011	13				—				4				17
	Changes related to settlements with taxing authorities	(5		)		(4		)		(1		)		(10		)
	Decreases related to the lapse of statute of limitations	—				—				(2		)		(2		)
	Unrecognized tax benefits – December 31, 2011	$	124			$	11			$	13			$	148
	Increases based on tax positions prior to 2012	4				—				1				5
	Decreases based on tax positions prior to 2012	(7		)		(1		)		(5		)		(13		)
	Increases (decreases) based on tax positions related to 2012	15				3				(1		)		17
	Changes related to settlements with taxing authorities	—				—				—				—
	Decreases related to the lapse of statute of limitations	—				—				(1		)		(1		)
	Unrecognized tax benefits – December 31, 2012	$	136			$	13			$	7			$	156
	Increases based on tax positions prior to 2013	—				2				5				7
	Decreases based on tax positions prior to 2013	(122		)		(16		)		(5		)		(143		)
	Increases based on tax positions related to 2013	16				—				53			(b)	69
	Changes related to settlements with taxing authorities	—				—				—				—
	Increases related to the lapse of statute of limitations	1				—				—				1
	Unrecognized tax benefits (detriments) – December 31, 2013	$	31			$	(1	)		$	60			$	90
	Total unrecognized tax benefits that, if recognized, would affect the effective tax rates as of December 31, 2011	$	1			$	—			$	—			$	1
	Total unrecognized tax benefits (detriments) that, if recognized, would affect the effective tax rates as of December 31, 2012	$	3			$	(1	)		$	(1	)		$	1
	Total unrecognized tax benefits that, if recognized, would affect the effective tax rates as of December 31, 2013	$	3			$	—			$	51		(b)	$	54
Reconciliation Of Changes In Liability For Interest On Unrecognized Tax Benefits	'																'
	A reconciliation of the change in the liability for interest on unrecognized tax benefits during the years ended December 31, 2011, 2012, and 2013, is as follows:
		Ameren Missouri				Ameren Illinois				Other				Ameren(a)
	Liability for interest – January 1, 2011	$	10			$	2			$	5			$	17
	Interest income for 2011	(3		)		(1		)		(7		)		(11		)
	Interest payment	(1		)		—				—				(1		)
	Liability for interest – December 31, 2011	$	6			$	1			$	(2	)		$	5
	Interest charges (income) for 2012	2				—				(1		)		1
	Liability for interest – December 31, 2012	$	8			$	1			$	(3	)		$	6
	Interest charges (income) for 2013	(8		)		(1		)		4				(5		)
	Liability for interest – December 31, 2013	$	—			$	—			$	1			$	1

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Schedule of Related Party Transactions	'
	The following table presents the impact on Ameren Missouri and Ameren Illinois of related party transactions for the years ended December 31, 2013, 2012, and 2011. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity.
	Agreement	Income Statement Line Item			Ameren		Ameren
					Missouri		Illinois
	Ameren Missouri power supply agreements	Operating Revenues	2013	$	3	$	(a)
	with Ameren Illinois		2012		(b)		(a)
			2011		2		(a)
	Ameren Missouri and Ameren Illinois	Operating Revenues	2013		21		1
	rent and facility services		2012		19		1
			2011		16		2
	Ameren Missouri and Ameren Illinois	Operating Revenues	2013		1		3
	miscellaneous support services		2012		1		(b)
			2011		5		1
	Total Operating Revenues		2013	$	25	$	4
			2012		20		1
			2011		23		3
	Ameren Illinois power supply	Purchased Power	2013	$	(a)	$	3
	agreements with Ameren Missouri		2012		(a)		(b)
			2011		(a)		2
	Ameren Illinois transmission	Purchased Power	2013		(a)		2
	services with ATXI		2012		(a)		3
			2011		(a)		3
	Total Purchased Power		2013	$	(a)	$	5
			2012		(a)		3
			2011		(a)		5
	Ameren Services support services	Other Operations and	2013	$	116	$	93
	agreement	Maintenance	2012		106		88
			2011		114		87
	Insurance premiums(c)	Other Operations and	2013		(b)		(a)
		Maintenance	2012		(b)		(a)
			2011		(b)		(a)
	Total Other Operations and		2013	$	116	$	93
	Maintenance Expenses		2012		106		88
			2011		114		87
	Money pool borrowings (advances)	Interest (Charges)	2013	$	(b)	$	(b)
		Income	2012		(b)		(b)
			2011		—		—
	(a)	Not applicable.
	(b)	Amount less than $1 million.
	(c)	Represents insurance premiums paid to Energy Risk Assurance Company, an affiliate for replacement power, property damage, and terrorism coverage.

Commitments_And_Contingencies_

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Schedule Of Insurance Coverage At Callaway Energy Center	'
	The following table presents insurance coverage at Ameren Missouri’s Callaway energy center at December 31, 2013. The property coverage and the nuclear liability coverage must be renewed on April 1 and January 1, respectively, of each year.
	Type and Source of Coverage	Maximum Coverages			Maximum Assessments
	Public liability and nuclear worker liability:
	American Nuclear Insurers	$	375		$	—
	Pool participation	13,241		(a)	128		(b)
		$	13,616	(c)	$	128
	Property damage:
	Nuclear Electric Insurance Limited	$	2,250	(d)	$	23	(e)
	European Mutual Association for Nuclear Insurance	500		(f)	—
		$	2,750		$	23
	Replacement power:
	Nuclear Electric Insurance Limited	$	490	(g)	$	9	(e)
	Missouri Energy Risk Assurance Company	$	64	(h)	$	—
	(a)	Provided through mandatory participation in an industrywide retrospective premium assessment program.
	(b)	Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $375 million in the event of an incident at any licensed United States commercial reactor, payable at $19 million per year.
	(c)	Limit of liability for each incident under the Price-Anderson Act liability provisions of the Atomic Energy Act of 1954, as amended. A company could be assessed up to $128 million per incident for each licensed reactor it operates with a maximum of $19 million per incident to be paid in a calendar year for each reactor. This limit is subject to change to account for the effects of inflation and changes in the number of licensed reactors.
	(d)	Nuclear Electric Insurance Limited provides $2.25 billion in property damage, decontamination, and premature decommissioning insurance. There is a $1.7 billion sublimit for non-radiation events, of which the top $200 million is a shared limit with other generators purchasing this coverage and includes one free reinstatement.
	(e)	All Nuclear Electric Insurance Limited insured plants could be subject to assessments should losses exceed the accumulated funds from Nuclear Electric Insurance Limited.
	(f)	European Mutual Association for Nuclear Insurance provides $500 million in excess of the $2.25 billion property coverage and $1.7 billion non-radiation coverage.
	(g)	Provides replacement power cost insurance in the event of a prolonged accidental outage at our nuclear energy center. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first eight weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Effective April 1, 2013, non-radiation events are sub-limited to $327.6 million.
	(h)	Provides replacement power cost insurance in the event of a prolonged accidental outage at our nuclear energy center. The coverage commences after the first 52 weeks of insurance coverage from Nuclear Electric Insurance Limited and is a weekly indemnity of $900,000 for 71 weeks in excess of the $3.6 million per week set forth above. Missouri Energy Risk Assurance Company LLC is an affiliate and has reinsured this coverage with third-party insurance companies. See Note 14 – Related Party Transactions for more information on this affiliate transaction.
Schedule Of Lease Obligations	'
	We lease various facilities, office equipment, plant equipment, and rail cars under capital and operating leases. The following table presents our lease obligations at December 31, 2013:
		Total			2014			2015		2016		2017		2018		After 5 Years
	Ameren:(a)
	Minimum capital lease payments(b)	$	556		$	32		$	33	$	33	$	33	$	32	$	393
	Less amount representing interest	257			27			27		27		27		26		123
	Present value of minimum capital lease payments	$	299		$	5		$	6	$	6	$	6	$	6	$	270
	Operating leases(c)	117			14			13		13		13		13		51
	Total lease obligations	$	416		$	19		$	19	$	19	$	19	$	19	$	321
	Ameren Missouri:
	Minimum capital lease payments(b)	$	556		$	32		$	33	$	33	$	33	$	32	$	393
	Less amount representing interest	257			27			27		27		27		26		123
	Present value of minimum capital lease payments	$	299		$	5		$	6	$	6	$	6	$	6	$	270
	Operating leases(c)	106			11			11		11		12		11		50
	Total lease obligations	$	405		$	16		$	17	$	17	$	18	$	17	$	320
	Ameren Illinois:
	Operating leases(c)	$	7		$	2		$	1	$	1	$	1	$	1	$	1
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
	(b)	See Properties under Part I, Item 2, and Note 3 – Property and Plant, Net, of this report for additional information.
	(c)	Amounts related to certain land-related leases have indefinite payment periods. The annual obligation of $2 million, $1 million and $1 million for Ameren, Ameren Missouri and Ameren Illinois for these items is included in the 2014 through 2018 columns, respectively.
Schedule Of Rental Expense	'
	The following table presents total rental expense, included in operating expenses, for the years ended December 31, 2013, 2012, and 2011:
		2013			2012			2011
	Ameren(a)	$	32		$	33		$	36
	Ameren Missouri	29			29			29
	Ameren Illinois	21			19			17
	(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
Schedule Of Estimated Purchased Commitments	'
	The table below presents our estimated commitments at December 31, 2013. Ameren’s and Ameren Missouri’s purchased power obligations include a 102-megawatt power purchase agreement with a wind farm operator that expires in 2024. Ameren’s and Ameren Illinois’ purchased power obligations include the Ameren Illinois power purchase agreements entered into as part of the IPA-administered power procurement process. Included in the Other column are minimum purchase commitments under contracts for equipment, design and construction, and meter reading services at December 31, 2013. Ameren's and Ameren Illinois' Other column also include obligations related to IEIMA. In addition, the Other column includes Ameren's and Ameren Missouri's obligations related to energy efficiency programs under the MEEIA as approved by the MoPSC's December 2012 electric rate order. Ameren Missouri expects to incur $48 million in 2014 and $64 million in 2015 for these energy efficiency programs. See Note 2 – Rate and Regulatory Matters for additional information about the IEIMA and MEEIA.
		Coal			Natural			Nuclear		Purchased		Methane		Other		Total
					Gas(a)			Fuel		Power(b)		Gas
	Ameren:(c)
	2014	$	620		$	323		$	64	$	308	$	3	$	201	$	1,519
	2015	642			179			63		164		4		143		1,195
	2016	664			90			81		78		4		76		993
	2017	676			45			58		55		4		50		888
	2018	120			28			57		52		5		51		313
	Thereafter	125			82			158		635		91		350		1,441
	Total	$	2,847		$	747		$	481	$	1,292	$	111	$	871	$	6,349
	Ameren Missouri:
	2014	$	620		$	62		$	64	$	19	$	3	$	127	$	895
	2015	642			32			63		19		4		101		861
	2016	664			19			81		19		4		40		827
	2017	676			11			58		19		4		26		794
	2018	120			8			57		19		5		27		236
	Thereafter	125			28			158		110		91		183		695
	Total	$	2,847		$	160		$	481	$	205	$	111	$	504	$	4,308
	Ameren Illinois:
	2014	$	—		$	261		$	—	$	289	$	—	$	23	$	573
	2015	—			147			—		145		—		24		316
	2016	—			71			—		59		—		24		154
	2017	—			34			—		36		—		24		94
	2018	—			20			—		33		—		24		77
	Thereafter	—			54			—		525		—		167		746
	Total	$	—		$	587		$	—	$	1,087	$	—	$	286	$	1,960
	(a)	Includes amounts for generation and for distribution.
	(b)	The purchased power amounts for Ameren and Ameren Illinois include 20-year agreements for renewable energy credits that were entered into in December 2010 with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.
	(c)	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
Schedule Of Estimated Obligations For Manufactured Gas Plant Remediation	'
	The following table presents, as of December 31, 2013, the estimated obligation to complete the remediation of these former MGP sites.
		Estimate						Recorded
		Low			High			Liability(a)
	Ameren	$	278		$	338		$	278
	Ameren Missouri	4			5			4
	Ameren Illinois	274			333			274
	(a)	Recorded liability represents the estimated minimum probable obligations, as no other amount within the range provided a better estimate.
Schedule Of Asbestos-Related Litigation Pending Lawsuits	'
	The following table presents the pending asbestos-related lawsuits filed against the Ameren Companies as of December 31, 2013:
	Ameren		Ameren	Ameren		Total(a)
			Missouri	Illinois
	1		47	50		71
	(a)	Total does not equal the sum of the subsidiary unit lawsuits because some of the lawsuits name multiple Ameren entities as defendants.

Divestiture_Transactions_and_D1

Divestiture Transactions and Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures	'
	The following table presents the components of discontinued operations in Ameren's consolidated statement of income (loss) for the years ended December 31, 2013, 2012 and 2011:
		Year ended
		2013				2012				2011
	Operating revenues	$	1,037			$	1,047			$	1,358
	Operating expenses	(1,207		)	(a)	(3,474		)	(b)	(1,150		)
	Operating income (loss)	(170		)		(2,427		)		208
	Other income (loss)	(1		)		—				1
	Interest charges	(39		)		(56		)		(64		)
	Income (loss) before income taxes	(210		)		(2,483		)		145
	Income tax (expense) benefit	(13		)		987				(56		)
	Income (loss) from discontinued operations, net of taxes	$	(223	)		$	(1,496	)		$	89
	(a)	Includes a $201 million pretax loss on disposal relating to the New AER divestiture.
	(b)	Includes a noncash pretax asset impairment charge of $628 million to reduce the carrying value of AERG’s Duck Creek energy center to its estimated fair value under held and used accounting guidance. In addition, includes a noncash pretax asset impairment charge of $1.95 billion to reduce the carrying values of all the AER coal and natural gas-fired energy centers, except the Joppa coal-fired energy center, to their estimated fair values, under held and used accounting guidance, as a result of the decision in December 2012 that Ameren intended to exit the Merchant Generation business.
	The following table presents the carrying amounts of the components of assets and liabilities segregated on Ameren's consolidated balance sheets as discontinued operations at December 31, 2013, and 2012:
		31-Dec-13				31-Dec-12
	Assets of discontinued operations
	Cash and cash equivalents	$	—			$	25
	Accounts receivable and unbilled revenue	5				102
	Materials and supplies	5				135
	Mark-to-market derivative assets	—				102
	Property and plant, net	142				748
	Accumulated deferred income taxes, net(a)	13				395
	Other assets	—				104
	Total assets of discontinued operations	$	165			$	1,611
	Liabilities of discontinued operations
	Accounts payable and other current obligations	$	5			$	141
	Mark-to-market derivative liabilities	—				63
	Long-term debt, net	—				824
	Asset retirement obligations(b)	40				97
	Pension and other postretirement benefits	—				40
	Other liabilities	—				28
	Total liabilities of discontinued operations	$	45			$	1,193
	Accumulated other comprehensive income (c)	$	—			$	19
	Noncontrolling interest(d)	$	—			$	8
	(a)	The December 31, 2013 balance primarily consists of deferred income tax assets related to the abandoned Meredosia and Hutsonville energy centers.
	(b)	Includes AROs associated with the abandoned Meredosia and Hutsonville energy centers of $31 million and $26 million at December 31, 2013, and 2012, respectively.
	(c)	Accumulated other comprehensive income related to discontinued operations included in “Accumulated other comprehensive loss” on Ameren’s December 31, 2012, consolidated balance sheet. This balance related to New AER assets and liabilities that were realized or removed from Ameren’s consolidated balance sheet either before or at the December 2, 2013 closing of the New AER divestiture.
	(d)	The 20% ownership interest of EEI not owned by Ameren was included in “Noncontrolling interests” on Ameren’s December 31, 2012, consolidated balance sheet. This noncontrolling interest was removed from Ameren’s consolidated balance sheet at the December 2, 2013 closing of the New AER divestiture.

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting Information, Profit (Loss) [Abstract]	'
Schedule Of Segment Reporting Information, By Segment	'
	The following table presents information about the reported revenues and specified items reflected in Ameren’s net income attributable to Ameren Corporation from continuing operations for the years ended December 31, 2013, 2012, and 2011, and total assets in continuing operations as of December 31, 2013, 2012, and 2011.
	Ameren
		Ameren		Ameren		Other				Intersegment			Consolidated
		Missouri		Illinois						Eliminations
	2013
	External revenues	$	3,516	$	2,307	$	15			$	—		$	5,838
	Intersegment revenues	25		4		2				(31		)	—
	Depreciation and amortization	454		243		9				—			706
	Interest and dividend income	27		2		1				—			30
	Interest charges	210		143		45				—			398
	Income taxes (benefit)	242		110		(41		)		—			311
	Net income (loss) attributable to Ameren Corporation from continuing operations	395		160		(43		)		—			512
	Capital expenditures	648		701		30			(a)	—			1,379
	Total assets	12,904		7,454		752				(233		)	20,877		(b)
	2012
	External revenues	$	3,252	$	2,524	$	5			$	—		$	5,781
	Intersegment revenues	20		1		3				(24		)	—
	Depreciation and amortization	440		221		12				—			673
	Interest and dividend income	32		—		—				—			32
	Interest charges	223		129		40				—			392
	Income taxes (benefit)	252		94		(39		)		—			307
	Net income (loss) attributable to Ameren Corporation from continuing operations	416		141		(41		)		—			516
	Capital expenditures	595		442		26			(a)	—			1,063
	Total assets	13,043		7,282		1,228				(934		)	20,619		(b)
	2011
	External revenues	$	3,360	$	2,784	$	4			$	—		$	6,148
	Intersegment revenues	23		3		3				(29		)	—
	Depreciation and amortization	408		215		20				—			643
	Interest and dividend income	30		1		—				—			31
	Interest charges	209		136		42				—			387
	Income taxes (benefit)	161		127		(34		)		—			254
	Net income (loss) attributable to Ameren Corporation from continuing operations	287		193		(49		)		—			431
	Capital expenditures	550		351		(20		)	(a)	—			881
	Total assets	12,757		7,213		1,211				(1,179		)	20,002		(b)
	.
	(a)	Includes the elimination of intercompany transfers.

Selected_Quarterly_Information1

Selected Quarterly Information (Tables)	12 Months Ended
	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]	'
Summary Of Selected Quarterly Information	'
	SELECTED QUARTERLY INFORMATION (Unaudited) (In millions, except per share amounts)
	Ameren	2013												2012
	Quarter ended (a)	31-Mar			30-Jun			30-Sep			31-Dec			31-Mar			30-Jun		30-Sep		31-Dec
	Operating revenues	$	1,475		$	1,403		$	1,638		$	1,322		$	1,412		$	1,402	$	1,709	$	1,258
	Operating income	185			261			567			171			159			347		570		112
	Net income (loss)(b)	(143		)	96			304			38			(403		)	210		374		(1,155		)
	Net income attributable to Ameren Corporation – continuing operations	$	54		$	105		$	305		$	48		$	38		$	164	$	302	$	12
	Net income (loss) attributable to Ameren Corporation – discontinued operations (b)	(199		)	(10		)	(3		)	(11		)	(441		)	47		72		(1,168		)
	Net income (loss) attributable to Ameren Corporation	$	(145	)	$	95		$	302		$	37		$	(403	)	$	211	$	374	$	(1,156	)
	Earnings per common share – basic – continuing operations	$	0.22		$	0.44		$	1.26		$	0.19		$	0.16		$	0.67	$	1.25	$	0.05
	Earnings (loss) per common share – basic – discontinued operations	(0.82		)	(0.05		)	(0.01		)	(0.04		)	(1.82		)	0.2		0.29		(4.81		)
	Earnings (loss) per common share – basic	$	(0.60	)	$	0.39		$	1.25		$	0.15		$	(1.66	)	$	0.87	$	1.54	$	(4.76	)
	Earnings per common share – diluted – continuing operations	$	0.22		$	0.44		$	1.25		$	0.19		$	0.16		$	0.67	$	1.25	$	0.05
	Earnings (loss) per common share – diluted – discontinued operations	(0.82		)	(0.05		)	(0.01		)	(0.04		)	(1.82		)	0.2		0.29		(4.81		)
	Earnings (loss) per common share – diluted	$	(0.60	)	$	0.39		$	1.24		$	0.15		$	(1.66	)	$	0.87	$	1.54	$	(4.76	)
	(a)	The sum of quarterly amounts, including per share amounts, may not equal amounts reported for year-to-date periods. This is due to the effects of rounding and to changes in the number of weighted-average shares outstanding each period.
	(b)	Includes pretax asset impairment charge of $2.6 billion recorded in discontinued operations during the year ended December 31, 2012. See Note 16 – Divestiture Transactions and Discontinued Operations under Part II, Item 8, for additional information.
	Ameren Missouri Quarter ended		Operating			Operating			Net income			Net income (loss)
			revenues			income			(loss)			available
												to common
												stockholder
	March 31, 2013		$	796		$	111		$	41		$	40
	March 31, 2012		691			78			22			21
	June 30, 2013		889			179			85			84
	June 30, 2012		844			269			144			143
	September 30, 2013		1,093			417			239			238
	September 30, 2012		1,064			429			237			236
	December 31, 2013		763			96			33			33
	December 31, 2012		673			69			16			16
	Ameren Illinois Quarter ended		Operating			Operating			Net income			Net income
			revenues			income						available
												to common
												stockholder
	March 31, 2013		$	684		$	85		$	32		$	31
	March 31, 2012		724			89			28			27
	June 30, 2013		516			87			32			31
	June 30, 2012		564			86			33			32
	September 30, 2013		547			158			77			77
	September 30, 2012		648			151			71			71
	December 31, 2013		564			85			22			21
	December 31, 2012		589			51			12			11

Summary_Of_Significant_Account3

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Mar. 31, 2014	Dec. 31, 2010
Accounting Policies [Line Items]	'		'		'		'	'
Unrecognized Tax Benefits	$90	[1]	$156	[1]	$148	[1]	$48	$246	[1]
Goodwill	411		411		'		'	'
Public Utilities, Property, Plant and Equipment, Amount of Indirect Disallowance of Costs of Recently Completed Plants	'		'		89		'	'
Tax grants received related to renewable energy properties	'		18		'		'	'
Book value	22		14		'		'	'
Ameren Illinois Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Unrecognized Tax Benefits	-1		13		11		'	56
Goodwill	411		411		'		'	'
Public Utilities, Area Serviced	40,000		'		'		'	'
Public Utilities, Estimated Population of Service Territory	3,100,000		'		'		'	'
Union Electric Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Unrecognized Tax Benefits	31		136		124		15	164
Public Utilities, Property, Plant and Equipment, Amount of Indirect Disallowance of Costs of Recently Completed Plants	'		'		89		'	'
Tax grants received related to renewable energy properties	'		18		'		'	'
Public Utilities, Area Serviced	24,000		'		'		'	'
Public Utilities, Estimated Population of Service Territory	2,800,000		'		'		'	'
Book value	22		14		'		'	'
Electric Energy Inc	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Percentage of EEI not owned by Ameren	'		20.00%		'		'	'
Voluntary Separation Offer	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Number Of Employee Positions Eliminated	'		'		340		'	'
Severance Costs	'		'		28		'	'
Voluntary Separation Offer | Union Electric Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Severance Costs	'		'		27		'	'
Minimum	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Percent of average depreciable cost	3.00%		3.00%		3.00%		'	'
Maximum	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Percent of average depreciable cost	4.00%		4.00%		4.00%		'	'
Power | Ameren Illinois Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Public Utilities, Number of Customers	1,200,000		'		'		'	'
Power | Union Electric Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Public Utilities, Number of Customers	1,200,000		'		'		'	'
Natural Gas | Ameren Illinois Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Public Utilities, Number of Customers	767,000		'		'		'	'
Natural Gas | Union Electric Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Public Utilities, Number of Customers	127,000		'		'		'	'
FAC | Union Electric Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Sharing Level For Fac	95.00%		'		'		'	'
Taum Sauk Energy Center | Union Electric Company	'		'		'		'	'
Accounting Policies [Line Items]	'		'		'		'	'
Public Utilities, Property, Plant and Equipment, Amount of Indirect Disallowance of Costs of Recently Completed Plants	'		'		$89		'	'
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Summary_Of_Significant_Account4

Summary Of Significant Accounting Policies (Schedule Of Material And Supplies) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Accounting Policies [Line Items]	'		'
Fuel	$144	[1]	$198	[1]
Gas stored underground	127		131
Other materials and supplies	255		241
Total materials and supplies	526		570
Union Electric Company	'		'
Accounting Policies [Line Items]	'		'
Fuel	144	[1]	198	[1]
Gas stored underground	17		18
Other materials and supplies	191		181
Total materials and supplies	352		397
Ameren Illinois Company	'		'
Accounting Policies [Line Items]	'		'
Fuel	'	[1]	'	[1]
Gas stored underground	110		113
Other materials and supplies	64		60
Total materials and supplies	$174		$173
[1]	(a)Consists of coal, oil, and propane.

Summary_Of_Significant_Account5

Summary Of Significant Accounting Policies (Schedule Of Rates Used For Allowance For Funds Used During Construction) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Union Electric Company	'	'	'
Accounting Policies [Line Items]	'	'	'
Allowance for funds used during construction, rate	8.00%	8.00%	8.00%
Ameren Illinois Company	'	'	'
Accounting Policies [Line Items]	'	'	'
Allowance for funds used during construction, rate	8.00%	9.00%	9.00%

Summary_Of_Significant_Account6

Summary Of Significant Accounting Policies (Schedule Of Amortization Expense) (Details) (Emission Allowances, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Finite-Lived Intangible Assets [Line Items]	'		'		'
Amortization expense	$13		$4		$3
Union Electric Company	'		'		'
Finite-Lived Intangible Assets [Line Items]	'		'		'
Amortization expense	1	[1]	1	[1]	1	[1]
Ameren Illinois Company	'		'		'
Finite-Lived Intangible Assets [Line Items]	'		'		'
Amortization expense	$13		$4		$3
[1]	(a)Less than $1 million.

Summary_Of_Significant_Account7

Summary Of Significant Accounting Policies (Schedule Of Excise Taxes) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accounting Policies [Line Items]	'	'	'
Excise tax expense	$213	$193	$194
Union Electric Company	'	'	'
Accounting Policies [Line Items]	'	'	'
Excise tax expense	152	139	137
Ameren Illinois Company	'	'	'
Accounting Policies [Line Items]	'	'	'
Excise tax expense	$61	$54	$57

Summary_Of_Significant_Account8

Summary Of Significant Accounting Policies (Basic and Diluted Earnings Per Share Calculations) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Accounting Policies [Abstract]	'	'	'	'	'	'	'	'	'		'		'
Continuing Operations	$48	$305	$105	$54	$12	$302	$164	$38	$512		$516		$431
Discontinued Operations	11	3	10	199	1,168	-72	-47	441	-223		-1,490		88
Net income (loss) attributable to Ameren Corporation	$37	$302	$95	($145)	($1,156)	$374	$211	($403)	$289		($974)		$519
Average Common Shares Outstanding - Basic	'	'	'	'	'	'	'	'	242.6		242.6		241.5
Assumed Settlement of Performance Share Units	'	'	'	'	'	'	'	'	1.9		0.4		0.6
Average Common Shares Outstanding - Diluted	'	'	'	'	'	'	'	'	244.5		243		242.1
Continuing Operations - Basic	$0.19	$1.26	$0.44	$0.22	$0.05	$1.25	$0.67	$0.16	$2.11		$2.13		$1.79
Discontinued Operations - Basic	($0.04)	($0.01)	($0.05)	($0.82)	($4.81)	$0.29	$0.20	($1.82)	($0.92)		($6.14)		$0.36
Earnings (Loss) per Common Share – Basic	$0.15	$1.25	$0.39	($0.60)	($4.76)	$1.54	$0.87	($1.66)	$1.19		($4.01)		$2.15
Continuing Operations - Diluted	$0.19	$1.25	$0.44	$0.22	$0.05	$1.25	$0.67	$0.16	$2.10		$2.13		$1.79
Discontinued Operations - Diluted	($0.04)	($0.01)	($0.05)	($0.82)	($4.81)	$0.29	$0.20	($1.82)	($0.92)		($6.14)		$0.36
Earnings (Loss) per Common Share – Diluted	$0.15	$1.24	$0.39	($0.60)	($4.76)	$1.54	$0.87	($1.66)	$1.18		($4.01)		$2.15
Average performance share units excluded from calculation	'	'	'	'	'	'	'	'	0.1	[1]	0.7	[1]	0	[1]
[1]	Weighted-average number of performance share units that were excluded from the “Assumed settlement of performance share units” provided above because the performance or market conditions related to the awards had not yet been met.

Summary_Of_Significant_Account9

Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Supplemental Cash Flow Information) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Cash Flow Information [Line Items]	'	'	'
Interest Paid, Net	$393	$433	$453
Income Taxes Paid, Net	8	1	-61
Continuing Operations [Member]	'	'	'
Supplemental Cash Flow Information [Line Items]	'	'	'
Interest Paid, Capitalized	20	17	27
Interest Paid, Net	362	384	393
Income Taxes Paid, Net	116	10	-47
Discontinued Operations [Member]	'	'	'
Supplemental Cash Flow Information [Line Items]	'	'	'
Interest Paid, Capitalized	17	13	3
Interest Paid, Net	31	49	60
Income Taxes Paid, Net	($108)	($9)	($14)

Recovered_Sheet1

Summary Of Significant Accounting Policies (Schedule Of Asset Retirement Obligations) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Balance	$349	[1]	$331	[1]
Liabilities incurred	0	[1]	'	[1]
Liabilities settled	-1	[1]	-1	[1]
Accretion in period	19	[1],[2]	18	[1],[2]
Change in estimates	2	[1],[3]	1	[1],[3]
Balance	369	[1]	349	[1]
Nuclear decommissioning trust fund	494		408
Union Electric Company	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Balance	346	[1]	328	[1]
Liabilities incurred	'	[1]	'	[1]
Liabilities settled	-1	[1]	-1	[1]
Accretion in period	19	[1],[2]	18	[1],[2]
Change in estimates	2	[1],[3]	1	[1],[3]
Balance	366	[1]	346	[1]
Nuclear decommissioning trust fund	494		408
Ameren Illinois Company	'		'
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]	'		'
Balance	3	[4]	3	[4]
Liabilities incurred	'	[4]	'	[4]
Liabilities settled	1	[4],[5]	1	[4],[5]
Accretion in period	1	[2],[4],[5]	1	[2],[4],[5]
Change in estimates	1	[4],[5]	1	[4],[5]
Balance	$3	[4]	$3	[4]
[1]	The nuclear decommissioning trust fund assets of $494 million and $408 million as of December 31, 2013, and 2012, respectively, are restricted for decommissioning of the Callaway energy center.
[2]	Accretion expense was recorded as an increase to regulatory assets at Ameren Missouri and Ameren Illinois.
[3]	Ameren Missouri changed its fair value estimates for asbestos removal in 2012 and 2013, and for certain CCR storage facilities in 2013.
[4]	Balance included in “Other deferred credits and liabilities” on the balance sheet.
[5]	Less than $1 million.

Rate_And_Regulatory_Matters_Na

Rate And Regulatory Matters (Narrative) (Details) (USD $)

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

60 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

Nov. 30, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2008

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Feb. 13, 2014

Apr. 30, 2011

Dec. 31, 2012

Dec. 31, 2005

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 18, 2013

Dec. 09, 2013

Dec. 09, 2013

Dec. 31, 2012

Dec. 09, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Feb. 28, 2014

design

design

FERC Relicensing

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

ATXI

Maximum

Maximum

Minimum

Pending Ferc Case [Member]

Midwest Independent Transmission System Operator, Inc [Member]

Fac Prudence Review

FERC Revenue Requirement Reconciliation

FERC Revenue Requirement Reconciliation

FERC Revenue Requirement Reconciliation

FERC Revenue Requirement Reconciliation

FERC Revenue Requirement Reconciliation

FERC Revenue Requirement Reconciliation

FERC Revenue Requirement Reconciliation

Customer [Domain]

Taum Sauk Energy Center

New Nuclear Energy Center COL

Electric Distribution

Fac Prudence Review

Entergy Refund

Pending Ferc Case [Member]

Final Rate Order

Final Rate Order

Accounting Authority Order Request

customer

Wholesale Distribution Rate Case

Wholesale Distribution Rate Case

Final Rate Order

Final Rate Order

Final Rate Order

Final Rate Order

Final Rate Order

IEMA Revenue Requirement Reconciliation

IEMA Revenue Requirement Reconciliation

IEMA Revenue Requirement Reconciliation

Potential Transmission Project Investments Through 2019

Union Electric Company

Ameren Illinois Company

Union Electric Company

Ameren Illinois Company

Pending Ferc Case [Member]

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

ATXI

Union Electric Company

customer

Power Purchase Agreement With Entergy Arkansas

Electric Distribution

MEEIA

Electric Distribution

Gas Distribution

Gas Distribution

Electric Distribution

IEIMA

IEIMA

Electric Distribution

IEIMA

IEIMA

New Nuclear Energy Center COL

Pending Ferc Case [Member]

New Nuclear Energy Center COL

customer

Subsequent Periods After September 30, 2009

Electric Distribution

Electric Distribution

Electric Distribution

Electric Distribution

Electric Distribution

Electric Distribution

Rate And Regulatory Matters [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Refund to Customers Under FAC

'

'

'

'

'

'

'

'

'

'

$18,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Authorized increase in revenue from utility service

'

'

'

'

'

'

'

'

'

'

'

'

'

260,000,000

'

'

'

'

'

'

'

'

32,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss Contingency, Settlement Agreement, Number of Wholesale Customers

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

'

'

'

'

'

'

'

'

'

Number of Wholesale Customers

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5

'

'

'

'

'

'

'

'

'

'

Rate of return on common equity

'

'

'

'

'

'

'

'

'

'

'

'

'

9.80%

'

'

'

'

'

'

'

9.10%

'

'

'

'

'

'

'

'

'

'

'

'

12.38%

'

'

'

'

'

'

'

'

'

Percent of capital structure composed of equity

'

'

'

'

'

'

'

'

'

'

'

'

'

52.30%

'

'

'

'

'

'

'

51.70%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Rate base

'

'

'

'

'

'

'

'

'

'

'

'

'

6,800,000,000

'

'

'

'

'

'

'

1,100,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Incentive Award if Energy Efficiency Goals Are Achieved

'

'

'

'

'

'

'

'

'

'

'

'

'

'

19,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Achieved Percentage of Energy Efficiency Earnings For Incentive Award

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Incentive Award if Energy Efficiency Goals Are Achieved, Period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Minimum Percentage of Energy Efficiency Goal Achievement For Company To Be Eligible For Incentive Award

'

'

'

'

'

'

'

'

'

'

'

'

'

'

70.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of Customers Filed Complaint Case

'

'

'

'

'

'

'

'

'

37

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Contested return on equity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9.80%

Customer Requested Rate on Equity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9.40%

Revenue Requirement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

788,000,000

765,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Authorized Decrease In Revenue From Utility Service

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-45,000,000

23,000,000

'

-68,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Disallowed costs associated with debt redemption

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15,000,000

15,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Current regulatory liabilities

'

216,000,000

100,000,000

'

'

57,000,000

18,000,000

'

'

'

'

'

'

'

'

'

159,000,000

82,000,000

'

13,000,000

8,000,000

'

'

'

'

'

'

65,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Noncurrent regulatory liabilities

'

1,705,000,000

1,589,000,000

'

'

1,041,000,000

917,000,000

'

'

'

'

'

'

'

'

'

664,000,000

672,000,000

'

'

'

'

'

'

'

'

'

'

55,000,000

'

'

'

'

'

'

'

10,000,000

[1]

0

[1]

0

[1]

0

[1]

10,000,000

[1]

0

[1]

'

'

Loss Contingency, Estimate of Possible Loss

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15,000,000

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from Legal Settlements

'

'

'

'

'

'

'

'

'

'

'

31,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Purchased power

'

502,000,000

780,000,000

952,000,000

'

127,000,000

78,000,000

104,000,000

'

'

'

24,000,000

25,000,000

'

'

'

380,000,000

705,000,000

853,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Department of Energy, Investing Funding Support, Number of Small Modular Reactor Designs

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Department of Energy, Investing Funding Support, Period

'

'5 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number Of Years COL is Valid For

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'40 years

'

'

'

'

'

'

'

'

'

'

'

Department of Energy, Investing Funding Support, Number of Small Modular Reactor Designs Awarded

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other Nonoperating Income

'

69,000,000

[2]

70,000,000

[2]

68,000,000

[2]

'

58,000,000

63,000,000

61,000,000

'

'

'

5,000,000

'

'

'

'

10,000,000

7,000,000

7,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reduction To Under-recovered Asset

'

'

'

'

'

'

'

'

'

'

'

2,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Customer Refund Liability, Current

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

26,000,000

'

'

'

'

'

'

'

'

Interest Expense

'

398,000,000

392,000,000

387,000,000

'

210,000,000

223,000,000

209,000,000

'

'

1,000,000

'

'

'

'

'

143,000,000

129,000,000

136,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000,000

'

'

'

'

'

'

'

'

Noncurrent regulatory assets

'

1,240,000,000

1,786,000,000

'

'

534,000,000

852,000,000

'

'

'

'

'

'

'

'

36,000,000

701,000,000

934,000,000

'

'

'

'

'

'

'

'

'

65,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5,000,000

'

Capital investments

'

'

'

'

'

'

'

'

$69,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$1,100,000,000

$100,000,000

'

$80,000,000

'

'

'

'

'

'

'

'

'

'

'

Number of years for proposed relicensing application filed with FERC

'

'

'

'

'40 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

Ameren Illinois' 2013 revenue requirement reconciliation adjustment calculated pursuant to the FERC's electric transmission formula ratemaking framework. This liability will be refunded to customers in 2015.

[2]

Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

Rate_And_Regulatory_Matters_Sc

Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	$156		$247
Noncurrent regulatory assets	1,240		1,786
Current regulatory liabilities	216		100
Noncurrent regulatory liabilities	1,705		1,589
Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	118		163
Noncurrent regulatory assets	534		852
Current regulatory liabilities	57		18
Noncurrent regulatory liabilities	1,041		917
Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	38		84
Noncurrent regulatory assets	701		934
Current regulatory liabilities	159		82
Noncurrent regulatory liabilities	664		672
Under-Recovered FAC	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	104	[1],[2]	145	[1],[2]
Under-Recovered FAC | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	104	[1],[2]	145	[1],[2]
Under-Recovered FAC | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	0	[1],[2]	0	[1],[2]
Under-Recovered Illinois Electric Power Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	1	[3]	0	[3]
Under-Recovered Illinois Electric Power Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	'	[3]	'	[3]
Under-Recovered Illinois Electric Power Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	1	[3]	0	[3]
Under-Recovered PGA	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	1	[3]	12	[3]
Under-Recovered PGA | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	0	[3]	5	[3]
Under-Recovered PGA | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	1	[3]	7	[3]
MTM Derivative Losses	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	50	[4]	90	[4]
Noncurrent regulatory assets	126	[4]	135	[4]
MTM Derivative Losses | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	14	[4]	13	[4]
Noncurrent regulatory assets	8	[4]	7	[4]
MTM Derivative Losses | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory assets	36	[4]	77	[4]
Noncurrent regulatory assets	118	[4]	128	[4]
Pension And Postretirement Benefit Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	184	[5]	772	[5]
Pension And Postretirement Benefit Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	44	[5]	348	[5]
Pension And Postretirement Benefit Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	140	[5]	424	[5]
Income Taxes	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	237	[6]	235	[6]
Noncurrent regulatory liabilities	41	[7]	46	[7]
Income Taxes | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	230	[6]	231	[6]
Noncurrent regulatory liabilities	38	[7]	42	[7]
Income Taxes | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	7	[6]	4	[6]
Noncurrent regulatory liabilities	3	[7]	4	[7]
Asset Retirement Obligation	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	5	[8]	5	[8]
Noncurrent regulatory liabilities	146	[8]	80	[8]
Asset Retirement Obligation | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[8]	0	[8]
Noncurrent regulatory liabilities	146	[8]	80	[8]
Asset Retirement Obligation | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	5	[8]	5	[8]
Noncurrent regulatory liabilities	'	[8]	0	[8]
Callaway Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	40	[1],[9]	44	[1],[9]
Callaway Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	40	[1],[9]	44	[1],[9]
Callaway Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[1],[9]	'	[1],[9]
Unamortized Loss On Reacquired Debt	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	151	[1],[10]	181	[1],[10]
Unamortized Loss On Reacquired Debt | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	77	[1],[10]	81	[1],[10]
Unamortized Loss On Reacquired Debt | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	74	[1],[10]	100	[1],[10]
Recoverable Costs Contaminated Facilities	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	271	[11]	248	[11]
Recoverable Costs Contaminated Facilities | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[11]	0	[11]
Recoverable Costs Contaminated Facilities | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	271	[11]	248	[11]
Storm Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	8	[12]	9	[12]
Storm Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	5	[12]	9	[12]
Storm Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	3	[12]	0	[12]
Demand-Side Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	58	[1],[13]	73	[1],[13]
Demand-Side Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	58	[1],[13]	73	[1],[13]
Demand-Side Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[1],[13]	0	[1],[13]
Reserve For Workers' Compensation Liabilities	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	12	[14]	12	[14]
Reserve For Workers' Compensation Liabilities | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	6	[14]	6	[14]
Reserve For Workers' Compensation Liabilities | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	6	[14]	6	[14]
Bad Debt Rider	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	8	[15]	12	[15]
Bad Debt Rider | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	'	[15]	'	[15]
Bad Debt Rider | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	8	[15]	12	[15]
Credit Facilities Fees	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	5	[16]	6	[16]
Credit Facilities Fees | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	5	[16]	6	[16]
Credit Facilities Fees | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[16]	0	[16]
Common Stock Issuance Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	4	[17]	7	[17]
Common Stock Issuance Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	4	[17]	7	[17]
Common Stock Issuance Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[17]	0	[17]
Construction Accounting For Pollution Control Equipment	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	22	[1],[18]	23	[1],[18]
Construction Accounting For Pollution Control Equipment | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	22	[1],[18]	23	[1],[18]
Construction Accounting For Pollution Control Equipment | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	'	[1],[18]	0	[1],[18]
Solar Rebates	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	27	[1],[19]	5	[1],[19]
Solar Rebates | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	27	[1],[19]	5	[1],[19]
Solar Rebates | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	0	[1],[20]	0	[1],[19]
IEMA Revenue Requirement Reconciliation	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	65	[21]	0	[21]
Current regulatory liabilities	65	[21]	0	[21]
Noncurrent regulatory liabilities	0	[21]	55	[21]
IEMA Revenue Requirement Reconciliation | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	0	[21]	0	[21]
Current regulatory liabilities	0	[21]	0	[21]
Noncurrent regulatory liabilities	0	[21]	0	[21]
IEMA Revenue Requirement Reconciliation | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	65	[21]	0	[21]
Current regulatory liabilities	65	[21]	0	[21]
Noncurrent regulatory liabilities	0	[21]	55	[21]
Other	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	25	[20],[22]	31	[20]
Noncurrent regulatory liabilities	10	[23]	4	[23]
Other | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	8	[20]	12	[20]
Noncurrent regulatory liabilities	10	[23]	4	[23]
Other | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory assets	12	[20]	19	[20]
Noncurrent regulatory liabilities	0	[23]	0	[23]
Over-Recovered FAC	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	26	[2]	0	[2]
Over-Recovered FAC | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	26	[2]	0	[2]
Over-Recovered FAC | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	0	[2]	0	[2]
Over-Recovered Illinois Electric Power Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	51	[3]	58	[3]
Over-Recovered Illinois Electric Power Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	0	[3]	0	[3]
Over-Recovered Illinois Electric Power Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	51	[3]	58	[3]
Over-Recovered PGA	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	34	[3]	15	[3]
Over-Recovered PGA | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	5	[3]	0	[3]
Over-Recovered PGA | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	29	[3]	15	[3]
MTM Derivative Gains	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	27	[4]	19	[4]
Noncurrent regulatory liabilities	1	[4]	2	[4]
MTM Derivative Gains | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	26	[4]	18	[4]
Noncurrent regulatory liabilities	1	[4]	2	[4]
MTM Derivative Gains | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	1	[4]	1	[4]
Noncurrent regulatory liabilities	'	[4]	'	[4]
Wholesale Distribution Refund	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	13	[24]	8	[24]
Wholesale Distribution Refund | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	0	[24]	0	[24]
Wholesale Distribution Refund | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Current regulatory liabilities	13	[24]	8	[24]
Removal Costs	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	1,438	[25]	1,347	[25]
Removal Costs | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	828	[25]	766	[25]
Removal Costs | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	610	[25]	581	[25]
Pension And Postretirement Benefit Costs Tracker	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	15	[26]	23	[26]
Pension And Postretirement Benefit Costs Tracker | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	15	[26]	23	[26]
Pension And Postretirement Benefit Costs Tracker | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	0	[26]	0	[26]
Energy Efficiency Rider	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	36	[27]	20	[27]
Energy Efficiency Rider | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	3	[27]	0	[27]
Energy Efficiency Rider | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	33	[27]	20	[27]
FERC Revenue Requirement Reconciliation	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	10	[28]	0	[28]
FERC Revenue Requirement Reconciliation | Union Electric Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	0	[28]	0	[28]
FERC Revenue Requirement Reconciliation | Ameren Illinois Company	'		'
Rate And Regulatory Matters [Line Items]	'		'
Noncurrent regulatory liabilities	$10	[28]	$0	[28]
[1]	These assets earn a return.
[2]	Under-recovered or over-recovered fuel costs to be recovered through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from customers that occurs over the next eight months.
[3]	Costs under- or over-recovered from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.
[4]	Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.
[5]	These costs are being amortized in proportion to the recognition of prior service costs (credits), transition obligations (assets), and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 11 – Retirement Benefits for additional information.
[6]	Offset to certain deferred tax liabilities for expected recovery of future income taxes when paid. This will be recovered over the expected life of the related assets.
[7]	Unamortized portion of investment tax credits, federal excess deferred taxes, and uncertain tax position tracker. The tracker is being amortized over three years, beginning in January 2013. The unamortized portion of investment tax credit is being amortized over the expected life of the underlying assets.
[8]	Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.
[9]	Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the remaining life of the energy center's current operating license, which expires in 2024.
[10]	Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.
[11]	The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 15 – Commitments and Contingencies for additional information.
[12]	Actual storm costs in a test year that exceed the MoPSC staff’s normalized storm costs for rate purposes. As approved by the December 2012 MoPSC electric rate order, the 2006, 2007, and 2008 storm costs are being amortized through December 2014. As approved by the May 2010 MoPSC electric rate order, the 2009 storm costs are being amortized through June 2015. The Ameren Illinois total includes 2013 storm costs deferred in accordance with the IEIMA. These costs are being amortized over a five-year period beginning in 2013.
[13]	Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing and evaluating customer energy efficiency and demand response programs. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized over a six-year period that began in July 2010. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013.
[14]	Reserve for workers’ compensation claims. The period of recovery will depend on the timing of actual expenditures.
[15]	A regulatory tracking mechanism for the difference between the level of bad debt expense incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2011 was refunded to customers from June 2012 through May 2013. The over-recovery relating to 2012 is being refunded to customers from June 2013 through May 2014. The over-recovery relating to 2013 will be refunded to customers from June 2013 through May 2014.
[16]	Ameren Missouri’s costs incurred to enter into and maintain the 2012 Ameren Missouri Credit Agreement. These costs are being amortized over five years, beginning in November 2012. These costs are being amortized to construction work in progress, which will be depreciated when assets are placed into service.
[17]	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to recover its portion of Ameren’s September 2009 common stock issuance costs. These costs are being amortized over five years, beginning in July 2010.
[18]	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment could be included in customer rates. These costs will be amortized over the expected life of the Sioux energy center, which is currently through 2033.
[19]	Costs associated with Ameren Missouri's solar rebate program beginning in August 2012 to fulfill Ameren Missouri's renewable energy portfolio requirement. The amortization period for these costs will be three years, commencing with the next Ameren Missouri electric rate case order.
[20]	The Ameren Illinois total includes Ameren Illinois Merger integration and optimization costs, which are amortized over four years, beginning in January 2012. The Ameren Illinois total also includes costs related to the 2013 natural gas delivery service rate case costs, which are being amortized over a two-year period that began in January 2014. The Ameren Illinois total also includes a portion of the unamortized debt fair value adjustment recorded upon Ameren's acquisition of IP. This portion is being amortized over the remaining life of the related debt. At Ameren Missouri, the balance primarily includes the cost of renewable energy credits to fulfill its renewable energy portfolio requirement. Costs incurred from January 2010 through July 2012 are being amortized over three years, beginning in January 2013.
[21]	The asset balance relates to the difference between Ameren Illinois' 2013 revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework, and the revenue requirement included in customer rates for 2013. Subject to ICC approval, this asset will be collected from customers in 2015. The liability balance relates to the difference between Ameren Illinois' 2012 revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for 2012. This liability will be refunded to customers in 2014.
[22]	The Ameren total includes $5 million for ATXI's revenue requirement reconciliation adjustments for 2012 and 2013 calculated pursuant to the FERC's electric transmission formula ratemaking framework. These adjustments will be collected from customers in 2014 for the 2012 revenue requirement reconciliation and in 2015 for the 2013 revenue requirement reconciliation.
[23]	Balance primarily includes the costs of renewable energy credits to fulfill Ameren Missouri's renewable energy portfolio requirement from August 2012 through December 2013, which were less than the amount included in rates. The amortization period for this over-recovery will be determined in a future Ameren Missouri electric rate case.
[24]	Estimated refund to wholesale electric customers. See 2011 Wholesale Distribution Rate Case above.
[25]	Estimated funds collected for the eventual dismantling and removal of plant from service, net of salvage value, upon retirement related to our rate-regulated operations.
[26]	A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs built into rates. For periods prior to August 2012, the MoPSC's December 2012 electric rate order directed the amortization to occur over five years, beginning in January 2013. For periods after August 2012, the amortization period will be determined in a future Ameren Missouri electric rate case.
[27]	The Ameren Illinois balance relates its regulatory tracking mechanism to recover its electric and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. This over-recovery will be refunded to customers over the following 12 months after the plan year. The Ameren Missouri balance relates to its MEEIA program costs incurred and projected lost revenues compared to the amount previously collected from customers. Beginning in January 2014, a MEEIA rider allows Ameren Missouri to collect from or refund to customers any annual difference in the actual amounts incurred and the projected amounts collected from customers for the MEEIA program costs and its projected lost revenues. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs and projected lost revenues are incurred.
[28]	Ameren Illinois' 2013 revenue requirement reconciliation adjustment calculated pursuant to the FERC's electric transmission formula ratemaking framework. This liability will be refunded to customers in 2015.

Property_And_Plant_Net_Schedul

Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified	equipment		agreement
			equipment
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	$23,701	[1],[2]	$22,796	[1],[2]
Accumulated depreciation and amortization	8,644	[1],[2]	8,346	[1],[2]
Property and plant, before construction work in progress	15,057	[1],[2]	14,450	[1],[2]
Property, Plant and Equipment, Net	16,205	[1],[2]	15,348	[1],[2]
Number of combustion turbine electric generation equipment under capital lease agreements	2		2
Number of capital lease agreements	2		2
Capital lease agreements, gross asset value	228		228
Total accumulated depreciation, capital lease agreements	56		52
Held-to-maturity Securities	299		304
Electric	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	21,726	[1],[2]	20,942	[1],[2]
Gas	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	1,975	[1],[2]	1,854	[1],[2]
Nuclear Fuel	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	246	[1],[2]	317	[1],[2]
Other Energy	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	902	[1],[2]	581	[1],[2]
Union Electric Company	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	16,377	[1]	16,031	[1]
Accumulated depreciation and amortization	6,766	[1]	6,614	[1]
Property and plant, before construction work in progress	9,611	[1]	9,417	[1]
Property, Plant and Equipment, Net	10,452	[1]	10,161	[1]
Union Electric Company | Electric	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	15,964	[1]	15,638	[1]
Union Electric Company | Gas	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	413	[1]	393	[1]
Union Electric Company | Nuclear Fuel	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	246	[1]	317	[1]
Union Electric Company | Other Energy	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	595	[1]	427	[1]
Ameren Illinois Company	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	6,988		6,446
Accumulated depreciation and amortization	1,627		1,495
Property and plant, before construction work in progress	5,361		4,951
Property, Plant and Equipment, Net	5,589		5,052
Ameren Illinois Company | Electric	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	5,426		4,985
Ameren Illinois Company | Gas	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	1,562		1,461
Ameren Illinois Company | Nuclear Fuel	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	0		0
Ameren Illinois Company | Other Energy	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	228		101
Other Affiliates [Member]	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	336		319
Accumulated depreciation and amortization	251		237
Property and plant, before construction work in progress	85		82
Property, Plant and Equipment, Net	164		135
Other Affiliates [Member] | Electric	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	336		319
Other Affiliates [Member] | Gas	'		'
Property, Plant and Equipment [Line Items]	'		'
Property and plant, at original cost	0		0
Other Affiliates [Member] | Nuclear Fuel	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	0		0
Other Affiliates [Member] | Other Energy	'		'
Property, Plant and Equipment [Line Items]	'		'
Construction work in progress	$79		$53
[1]	(a)Amounts in Ameren and Ameren Missouri include two electric generation CTs under separate capital lease agreements. The gross cumulative asset value of those agreements was $228 million at December 31, 2013, and $228 million at December 31, 2012. The total accumulated depreciation associated with the two CTs was $56 million and $52 million at December 31, 2013, and 2012, respectively. In addition, Ameren Missouri has investments in debt securities, which were classified as held-to-maturity, related to the two CTs from the city of Bowling Green and Audrain County. As of December 31, 2013, and 2012, the carrying value of these debt securities was $299 million and $304 million, respectively.
[2]	(b)Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Property_And_Plant_Net_Accrued

Property And Plant, Net (Accrued Capital Expenditures) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Property, Plant and Equipment [Line Items]	'		'		'
Accrued capital expenditures	$175	[1]	$107	[1]	$97	[1]
Union Electric Company	'		'		'
Property, Plant and Equipment [Line Items]	'		'		'
Accrued capital expenditures	74		63		73
Ameren Illinois Company	'		'		'
Property, Plant and Equipment [Line Items]	'		'		'
Accrued capital expenditures	86		37		18
Nuclear Fuel	'		'		'
Property, Plant and Equipment [Line Items]	'		'		'
Accrued capital expenditures	8	[1]	8	[1]	36	[1]
Nuclear Fuel | Union Electric Company	'		'		'
Property, Plant and Equipment [Line Items]	'		'		'
Accrued capital expenditures	$8		$8		$36
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

ShortTerm_Debt_And_Liquidity_N

Short-Term Debt And Liquidity (Narrative) (Details) (USD $)

Nov. 14, 2012

Dec. 31, 2013

Dec. 31, 2013

Nov. 14, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Illinois Credit Agreement 2012

Illinois Credit Agreement 2012

Illinois Credit Agreement 2012

Missouri Credit Agreement 2012

Missouri Credit Agreement 2012

Missouri Credit Agreement 2012

Credit Agreements 2012

Unilateral Borrowing Agreement

Multiyear Credit Facility

Multiyear Credit Facility

Commercial Paper

Utilities

Utilities

Maximum

Ameren Illinois Company

Maximum

Union Electric Company

Ameren Illinois Company

lender

Maximum

Line of Credit Facility [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of credit facility, maximum borrowing capacity

$1,100,000,000

$1,300,000,000

$800,000,000

$1,000,000,000

$1,200,000,000

$800,000,000

$1,700,000,000

$500,000,000

$2,100,000,000

'

'

'

'

Number of lenders

'

'

'

'

'

'

'

'

24

'

'

'

'

Line of credit facility, maximum borrowing capacity, per lender

'

'

'

'

'

'

'

'

125,000,000

'

'

'

'

Commercial paper maximum issuance

'

'

'

'

'

'

'

'

'

'

500,000,000

'

'

Actual debt-to-capital ratio

'

'

0.44

'

'

0.47

'

'

0.48

0.65

'

'

'

Minimum ratio of consolidated funds from operations plus interest expense to consolidated interest expense as of balance sheet date

'

'

'

'

'

'

'

'

'2.0 to 1.0

'

'

'

'

Current ratio of consolidated funds from operations plus interest expense to consolidated interest expense as of balance sheet date

'

'

'

'

'

'

'

'

'5.3 to 1.0

'

'

'

'

Covenant terms, default provisions, maximum indebtedness

'

'

'

'

'

'

$50,000,000

'

'

'

'

'

'

Short Term Debt, Weighted Average Interest Rate During Period

'

'

'

'

'

'

'

'

'

'

'

0.14%

0.13%

Letters of credit portion of aggregate commitment

'

'

'

'

'

'

'

'

25.00%

'

'

'

'

ShortTerm_Debt_And_Liquidity_S

Short-Term Debt And Liquidity (Schedule Of Maximum Aggregate Amount Available On Credit Agreements) (Details) (USD $)	Nov. 14, 2012	Dec. 31, 2013	Dec. 31, 2013	Nov. 14, 2012	Dec. 31, 2013	Dec. 31, 2013
	Illinois Credit Agreement 2012	Illinois Credit Agreement 2012	Illinois Credit Agreement 2012	Missouri Credit Agreement 2012	Missouri Credit Agreement 2012	Missouri Credit Agreement 2012
		Parent Company	Ameren Illinois Company		Parent Company	Union Electric Company
Line of Credit Facility [Line Items]	'	'	'	'	'	'
Line of credit facility, maximum borrowing capacity	$1,100,000,000	$300,000,000	$800,000,000	$1,000,000,000	$500,000,000	$800,000,000

ShortTerm_Debt_And_Liquidity_S1

Short-Term Debt And Liquidity Short-Term Debt And Liquidity (Commercial Paper) (Details) (Commercial Paper, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Commercial Paper	'	'
Line of Credit Facility [Line Items]	'	'
Average Daily Commercial Paper Borrowings Outstanding	$54	$49
Commercial paper outstanding	368	'
Weighted average interest rate	0.56%	0.92%
Peak short-term borrowings	$368	$229
Peak short-term borrowings interest rate	0.85%	1.25%

LongTerm_Debt_And_Equity_Finan2

Long-Term Debt And Equity Financings (Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

3 Months Ended

1 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

1 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Oct. 31, 2013

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Jan. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Oct. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Oct. 31, 2013

Dec. 31, 2012

Nov. 30, 2012

Aug. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 11, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Sep. 20, 2012

Aug. 27, 2012

Dec. 31, 2013

Jan. 31, 2014

DRPlus

DRPlus

401 (K)

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Missouri and Ameren Illinois

Senior Secured Notes 4.80% Due 2043

Senior Secured Notes 4.80% Due 2043

Senior Secured Notes 8.875% Due 2013

Senior Secured Notes 8.875% Due 2013

1993 5.45% Series due 2028

1993 5.45% Series due 2028

1993 5.45% Series due 2028

4.65% Senior secured notes due 2013

4.65% Senior secured notes due 2013

4.65% Senior secured notes due 2013

Series1992 B 6.20% Due 2012

Senior Secured Notes, 2.70%, Due 2022

Senior Secured Notes, 2.70%, Due 2022

Senior Secured Notes, 2.70%, Due 2022

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

5.25% Senior secured notes due 2012

Series A 2000 5.50% Due 2014

Minimum

Subsequent Event

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Secured Debt

Secured Debt

Secured Debt

Environmental Improvement And Pollution Control Revenue Bonds

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Long-Term Debt And Equity Financings [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock, authorized

100,000,000

'

'

'

'

'

7,500,000

'

'

2,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock, par value

$0.01

'

'

'

'

'

$1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock, shares outstanding

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock, shares authorized

400,000,000

400,000,000

'

4,000,000

6,000,000

'

150,000,000

150,000,000

'

45,000,000

45,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock, shares issued

'

0

2,200,000

'

'

2,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock, value of shares issued

'

'

$65,000,000

'

'

$65,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument face amount

'

'

'

'

'

'

'

'

1,000,000

[1]

'

'

'

280,000,000

[2]

0

[2]

'

[3]

150,000,000

[3]

1,000,000

[4]

'

44,000,000

[4]

'

[5]

'

200,000,000

[5]

'

400,000,000

400,000,000

[2],[6]

400,000,000

[2],[6]

485,000,000

485,000,000

[5],[7]

485,000,000

[5],[7]

485,000,000

'

'

'

'

Long-term debt interest rate

'

'

'

'

'

'

'

'

'

'

'

'

4.80%

'

8.88%

'

5.45%

5.45%

'

4.65%

4.65%

'

6.20%

2.70%

2.70%

'

3.90%

3.90%

'

3.90%

5.25%

5.50%

'

'

Proceeds from issuance of secured debt

'

'

'

'

'

'

'

'

'

'

'

'

276,000,000

'

'

'

'

'

'

'

'

'

'

397,000,000

'

'

478,000,000

'

'

'

'

'

'

'

Redemptions of long-term debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

150,000,000

'

44,000,000

'

'

200,000,000

'

'

1,000,000

'

'

'

'

'

'

'

173,000,000

51,000,000

'

163,000,000

Bonds interest rate assumption

'

'

'

'

'

'

'

'

'

'

'

6.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividend rate on preferred shares, percentage

'

'

'

'

'

'

'

'

'

'

'

7.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Excess in indebtedness upon default of maturity

$25,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock equity to capitalization ratio

'

'

'

'

'

'

'

'

'

55.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

30.00%

'

[1]

These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy.

[2]

These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.

[3]

These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the CILCO mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the CILCO first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2023.

[4]

These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.

[5]

These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.

[6]

Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.

[7]

Ameren Missouri has agreed, during the life of these notes, not to optionally redeem, purchase or otherwise retire in full its first mortgage bonds. Ameren Missouri has also agreed to prevent a first mortgage bond release date from occurring as long as any of the 8.45% senior secured notes due 2039 and any of the 3.90% senior secured notes due 2042 remain outstanding.

LongTerm_Debt_And_Equity_Finan3

Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Jan. 31, 2014

Sep. 20, 2012

Dec. 31, 2013

Oct. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Sep. 11, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Aug. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Oct. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Nov. 30, 2012

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Parent Company

Parent Company

Parent Company

Parent Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

8.875% Senior unsecured notes due 2014

8.875% Senior unsecured notes due 2014

City Of Bowling Green Capital Lease Peno Creek Ct

City Of Bowling Green Capital Lease Peno Creek Ct

Audrain County Capital Lease Audrain County Ct

Audrain County Capital Lease Audrain County Ct

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

5.25% Senior secured notes due 2012

4.65% Senior secured notes due 2013

4.65% Senior secured notes due 2013

4.65% Senior secured notes due 2013

5.50% Senior secured notes due 2014

5.50% Senior secured notes due 2014

4.75% Senior secured notes due 2015

4.75% Senior secured notes due 2015

5.40% Senior secured notes due 2016

5.40% Senior secured notes due 2016

6.40% Senior secured notes due 2017

6.40% Senior secured notes due 2017

6.00% Senior secured notes due 2018

6.00% Senior secured notes due 2018

6.00% Senior secured notes due 2018

5.10% Senior secured notes due 2018

5.10% Senior secured notes due 2018

5.10% Senior secured notes due 2018

6.70% Senior secured notes due 2019

6.70% Senior secured notes due 2019

6.70% Senior secured notes due 2019

5.10% Senior secured notes due 2019

5.10% Senior secured notes due 2019

5.10% Senior secured notes due 2019

5.00% Senior secured notes due 2020

5.00% Senior secured notes due 2020

5.50% Senior secured notes due 2034

5.50% Senior secured notes due 2034

5.30% Senior secured notes due 2037

5.30% Senior secured notes due 2037

8.45% Senior secured notes due 2039

8.45% Senior secured notes due 2039

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

Senior Secured Notes 8.875% Due 2013

Senior Secured Notes 8.875% Due 2013

Senior Secured Notes 6.20% Due 2016

Senior Secured Notes 6.20% Due 2016

Senior Secured Notes 6.25% Due 2016

Senior Secured Notes 6.25% Due 2016

Senior Secured Notes 6.125% Due 2017

Senior Secured Notes 6.125% Due 2017

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes, 2.70%, Due 2022

Senior Secured Notes, 2.70%, Due 2022

Senior Secured Notes, 2.70%, Due 2022

Senior Secured Notes 6.125% Due 2028

Senior Secured Notes 6.125% Due 2028

Senior Secured Notes 6.70% Due 2036

Senior Secured Notes 6.70% Due 2036

Senior Secured Notes 6.70% Due 2036

Senior Secured Notes 6.70% Due 2036

Senior Secured Notes 4.80% Due 2043

Senior Secured Notes 4.80% Due 2043

1992 Series due 2022

1992 Series due 2022

1993 5.45% Series due 2028

1993 5.45% Series due 2028

1993 5.45% Series due 2028

1998 Series A due 2033

1998 Series A due 2033

1998 Series B due 2033

1998 Series B due 2033

1998 Series C due 2033

1998 Series C due 2033

Series1992 B 6.20% Due 2012

Series A 2000 5.50% Due 2014

Series 1993 5.90% Due 2023

Series 1993 5.90% Due 2023

Series 1994 A 5.70% Due 2024

Series 1994 A 5.70% Due 2024

Series C-1 1993 5.95% Due 2026

Series C-1 1993 5.95% Due 2026

Series C-2 1993 5.70% Due 2026

Series C-2 1993 5.70% Due 2026

Series B-1 1993 Due 2028

Series B-1 1993 Due 2028

Series1998A 5.40% Due 2028

Series1998A 5.40% Due 2028

Series1998B 5.40% Due 2028

Series1998B 5.40% Due 2028

Debt Instrument [Line Items]

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'

Debt instrument face amount

'

'

'

'

$425,000,000

$425,000,000

'

'

'

'

'

'

'

'

$1,000,000

[1]

'

'

[2]

'

$200,000,000

[2]

$104,000,000

[2]

$104,000,000

[2]

$114,000,000

[2]

$114,000,000

[2]

$260,000,000

[2]

$260,000,000

[2]

$425,000,000

[2]

$425,000,000

[2]

$179,000,000

[2],[3]

$179,000,000

[2],[3]

$179,000,000

$199,000,000

[2]

$199,000,000

[2]

$199,000,000

[4]

$329,000,000

[2],[3]

$329,000,000

[2],[3]

$329,000,000

$244,000,000

[2]

$244,000,000

[2]

$244,000,000

$85,000,000

[2]

$85,000,000

[2]

$184,000,000

[2]

$184,000,000

[2]

$300,000,000

[2]

$300,000,000

[2]

$350,000,000

[2],[3]

$350,000,000

[2],[3]

$485,000,000

[2],[3]

$485,000,000

[2],[3]

$485,000,000

$485,000,000

'

[5]

$150,000,000

[5]

$54,000,000

[5]

$54,000,000

[5]

$75,000,000

[6]

$75,000,000

[6]

$250,000,000

[6],[7]

$250,000,000

[6],[7]

$144,000,000

[6],[7]

$144,000,000

[6],[7]

$144,000,000

$313,000,000

[6],[7]

$313,000,000

[6],[7]

$313,000,000

$400,000,000

[6],[7]

$400,000,000

[6],[7]

$400,000,000

$60,000,000

[6]

$60,000,000

[6]

$61,000,000

[6]

$61,000,000

[6]

$42,000,000

[5]

$42,000,000

[5]

$280,000,000

[6]

$0

[6]

$47,000,000

[8],[9]

$47,000,000

[8],[9]

$1,000,000

[10]

'

$44,000,000

[10]

$60,000,000

[8],[9]

$60,000,000

[8],[9]

$50,000,000

[8],[9]

$50,000,000

[8],[9]

$50,000,000

[8],[9]

$50,000,000

[8],[9]

'

'

$32,000,000

[11]

$32,000,000

[11]

$36,000,000

[1]

$36,000,000

[1]

$35,000,000

[12]

$35,000,000

[12]

$8,000,000

[12]

$8,000,000

[12]

$17,000,000

[12],[8]

$17,000,000

[12],[8]

$19,000,000

[1]

$19,000,000

[1]

$33,000,000

[1]

$33,000,000

[1]

Capital lease obligations

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'

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'

59,000,000

64,000,000

240,000,000

240,000,000

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Fair-market value adjustments

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4,000,000

4,000,000

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Long-term debt, gross

'

'

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'

3,764,000,000

4,013,000,000

'

'

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'

1,863,000,000

1,733,000,000

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Less: Unamortized discount and premium

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1,000,000

'

'

7,000,000

7,000,000

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7,000,000

6,000,000

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'

Less: Maturities due within one year

-534,000,000

-355,000,000

-425,000,000

'

'

'

-109,000,000

-205,000,000

'

'

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'

-150,000,000

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'

'

'

Long-term Debt, Net

$5,504,000,000

$5,802,000,000

'

$424,000,000

'

'

$3,648,000,000

$3,801,000,000

'

'

'

'

$1,856,000,000

$1,577,000,000

'

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'

'

'

'

Long-term debt interest rate

'

'

'

'

8.88%

'

'

'

'

'

'

'

'

'

'

5.25%

4.65%

4.65%

'

5.50%

'

4.75%

'

5.40%

'

6.40%

'

6.00%

'

6.00%

5.10%

'

5.10%

6.70%

'

6.70%

5.10%

'

5.10%

5.00%

'

5.50%

'

5.30%

'

8.45%

'

3.90%

'

3.90%

3.90%

8.88%

'

6.20%

'

6.25%

'

6.13%

'

6.25%

'

6.25%

9.75%

'

9.75%

2.70%

'

2.70%

6.13%

'

6.70%

'

6.70%

'

4.80%

'

'

'

5.45%

5.45%

'

'

'

'

'

'

'

6.20%

5.50%

5.90%

'

5.70%

'

5.95%

'

5.70%

'

'

'

5.40%

'

5.40%

'

Long-term debt maturity date

'

'

'

'

'2014

'

'

'

'2022

'

'2033

'

'

'

'

'

'2013

'

'

'2014

'

'2015

'

'2016

'

'2017

'

'2018

'

'

'2018

'

'

'2019

'

'

'2019

'

'

'2020

'

'2034

'

'2037

'

'2039

'

'2042

'

'

'

'2013

'

'2016

'

'2016

'

'2017

'

'2018

'

'

'2018

'

'

'2022

'

'

'2028

'

'2036

'

'2036

'

'2043

'

'2022

'

'2028

'

'

'2033

'

'2033

'

'2033

'

'

'

'2023

'

'2024

'

'2026

'

'2026

'

'2028

'

'2028

'

'2028

'

Debt instrument, interest rate, maximum

'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

18.00%

'

'

'

'

18.00%

'

18.00%

'

18.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Redemption price, percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

100.00%

'

100.00%

'

100.00%

'

100.00%

'

100.00%

'

100.00%

'

100.00%

'

[1]

These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy.

[2]

These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.

[3]

Ameren Missouri has agreed, during the life of these notes, not to optionally redeem, purchase or otherwise retire in full its first mortgage bonds. Ameren Missouri has also agreed to prevent a first mortgage bond release date from occurring as long as any of the 8.45% senior secured notes due 2039 and any of the 3.90% senior secured notes due 2042 remain outstanding.

[4]

Amount is less than $1 million.

[5]

These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the CILCO mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the CILCO first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2023.

[6]

These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.

[7]

Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.

[8]

Interest rates, and periods during which such rates apply, vary depending on our selection of defined rate modes. Maximum interest rates could range up to 18% depending on the series of bonds. The average interest rates for 2013 and 2012 were as follows: 2013 2012Ameren Missouri 1992 Series0.17% 0.30%Ameren Missouri 1998 Series A0.34% 0.65%Ameren Missouri 1998 Series B0.33% 0.64%Ameren Missouri 1998 Series C0.34% 0.64%Ameren Illinois 1993 Series B-10.14% 0.22%

[9]

These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri's senior secured notes. The bonds are also backed by an insurance guarantee policy.

[10]

These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage bond indenture and are secured by substantially all Ameren Missouri property and franchises. The bonds are callable at 100% of par value. Less than $1 million principal amount of the bonds remain outstanding.

[11]

These bonds are first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture and are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value.

[12]

The bonds are callable at 100% of par value.

LongTerm_Debt_And_Equity_Finan4

Long-Term Debt And Equity Financings (Schedule Of Average Interest Rates) (Details)

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Sep. 20, 2012

Sep. 11, 2012

1992 Series due 2022

1992 Series due 2022

1998 Series A due 2033

1998 Series A due 2033

1998 Series B due 2033

1998 Series B due 2033

1998 Series C due 2033

1998 Series C due 2033

Series B-1 1993 Due 2028

Series B-1 1993 Due 2028

Secured Debt

Secured Debt

Secured Debt

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

Union Electric Company

Union Electric Company

Union Electric Company

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term debt interest rate

'

'

'

'

'

'

'

'

'

'

3.90%

3.90%

3.90%

Debt instrument, interest rate during period

0.17%

0.30%

0.34%

0.65%

0.33%

0.64%

0.34%

0.64%

0.14%

0.22%

'

'

'

LongTerm_Debt_And_Equity_Finan5

Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Debt Instrument [Line Items]	'		'
2014	$534		'
2015	120		'
2016	395		'
2017	681		'
2018	840		'
Thereafter	3,478		'
Total	6,048		'
Parent Company	'		'
Debt Instrument [Line Items]	'		'
2014	425		'
2015	'		'
2016	'		'
2017	'		'
2018	'		'
Thereafter	'		'
Total	425		'
Unamortized discount and premium	'		1
Union Electric Company	'		'
Debt Instrument [Line Items]	'		'
2014	109	[1]	'
2015	120	[1]	'
2016	266	[1]	'
2017	431	[1]	'
2018	383	[1]	'
Thereafter	2,455	[1]	'
Total	3,764	[1]	'
Unamortized discount and premium	7		7
Ameren Illinois Company	'		'
Debt Instrument [Line Items]	'		'
2014	'	[1],[2]	'
2015	'	[1],[2]	'
2016	129	[1],[2]	'
2017	250	[1],[2]	'
2018	457	[1],[2]	'
Thereafter	1,023	[1],[2]	'
Total	1,859	[1],[2]	'
Unamortized discount and premium	7		6
Fair value adjustments	$4		'
[1]	Excludes unamortized discount and premium of $7 million and $7 million at Ameren Missouri and Ameren Illinois, respectively.
[2]	Excludes $4 million related to Ameren Illinois’ long-term debt fair-market value adjustments, which are being amortized to interest expense over the remaining life of the debt.

LongTerm_Debt_And_Equity_Finan6

Long-Term Debt And Equity Financings (Schedule Of Outstanding Preferred Stock) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Long-Term Debt And Equity Financings [Line Items]	'		'
Preferred stock, par value	$0.01		'
Preferred stock, authorized	100,000,000		'
Preferred stock, shares outstanding	0		'
Preferred stock, issued	$142		$142
Preferred stock, voluntary liquidation	$106		'
Union Electric Company	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Preferred stock, par value	$1		'
Preferred stock, authorized	7,500,000		'
Preferred stock, issued	80		80
Union Electric Company | Par Value $100 [Member]	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Preferred stock, par value	$100		'
Preferred stock, authorized	25,000,000		'
Union Electric Company | $3.50 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$3.50		'
Preferred stock, shares outstanding	130,000		'
Preferred stock, redemption price per share	$110		'
Preferred stock, issued	13		13
Union Electric Company | $3.70 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$3.70		'
Preferred stock, shares outstanding	40,000		'
Preferred stock, redemption price per share	$105		'
Preferred stock, issued	4		4
Union Electric Company | $4.00 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$4		'
Preferred stock, shares outstanding	150,000		'
Preferred stock, redemption price per share	$106		'
Preferred stock, issued	15		15
Union Electric Company | $4.30 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$4.30		'
Preferred stock, shares outstanding	40,000		'
Preferred stock, redemption price per share	$105		'
Preferred stock, issued	4		4
Union Electric Company | $4.50 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$4.50		'
Preferred stock, shares outstanding	213,595		'
Preferred stock, redemption price per share	$110	[1]	'
Preferred stock, issued	21		21
Union Electric Company | $4.56 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$4.56		'
Preferred stock, shares outstanding	200,000		'
Preferred stock, redemption price per share	$102		'
Preferred stock, issued	20		20
Union Electric Company | $4.75 Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$4.75		'
Preferred stock, shares outstanding	20,000		'
Preferred stock, redemption price per share	$102		'
Preferred stock, issued	2		2
Union Electric Company | $5.50 Series A	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, per-dollar amount	$5.50		'
Preferred stock, shares outstanding	14,000		'
Preferred stock, redemption price per share	$110		'
Preferred stock, issued	1		1
Ameren Illinois Company	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Preferred stock, authorized	2,600,000		'
Preferred stock, issued	62		62
Ameren Illinois Company | Par Value $100 [Member]	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Preferred stock, par value	$100		'
Preferred stock, authorized	2,000,000		'
Ameren Illinois Company | 4.00% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.00%		'
Preferred stock, shares outstanding	144,275		'
Preferred stock, redemption price per share	$101		'
Preferred stock, issued	14		14
Ameren Illinois Company | 4.08% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.08%		'
Preferred stock, shares outstanding	45,224		'
Preferred stock, redemption price per share	$103		'
Preferred stock, issued	5		5
Ameren Illinois Company | 4.20% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.20%		'
Preferred stock, shares outstanding	23,655		'
Preferred stock, redemption price per share	$104		'
Preferred stock, issued	2		2
Ameren Illinois Company | 4.25% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.25%		'
Preferred stock, shares outstanding	50,000		'
Preferred stock, redemption price per share	$102		'
Preferred stock, issued	5		5
Ameren Illinois Company | 4.26% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.26%		'
Preferred stock, shares outstanding	16,621		'
Preferred stock, redemption price per share	$103		'
Preferred stock, issued	2		2
Ameren Illinois Company | 4.42% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.42%		'
Preferred stock, shares outstanding	16,190		'
Preferred stock, redemption price per share	$103		'
Preferred stock, issued	2		2
Ameren Illinois Company | 4.70% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.70%		'
Preferred stock, shares outstanding	18,429		'
Preferred stock, redemption price per share	$103		'
Preferred stock, issued	2		2
Ameren Illinois Company | 4.90% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.90%		'
Preferred stock, shares outstanding	73,825		'
Preferred stock, redemption price per share	$102		'
Preferred stock, issued	7		7
Ameren Illinois Company | 4.92% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	4.92%		'
Preferred stock, shares outstanding	49,289		'
Preferred stock, redemption price per share	$104		'
Preferred stock, issued	5		5
Ameren Illinois Company | 5.16% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	5.16%		'
Preferred stock, shares outstanding	50,000		'
Preferred stock, redemption price per share	$102		'
Preferred stock, issued	5		5
Ameren Illinois Company | 6.625% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	6.63%		'
Preferred stock, shares outstanding	124,274		'
Preferred stock, redemption price per share	$100		'
Preferred stock, issued	12		12
Ameren Illinois Company | 7.75% Series	'		'
Long-Term Debt And Equity Financings [Line Items]	'		'
Dividend rate on preferred shares, percentage	7.75%		'
Preferred stock, shares outstanding	4,542		'
Preferred stock, redemption price per share	$100		'
Preferred stock, issued	$1		$1
[1]	In the event of voluntary liquidation, $105.50

LongTerm_Debt_And_Equity_Finan7

Long-Term Debt And Equity Financings (Aggregate Principal Amount of Senior Notes) (Details) (USD $)

12 Months Ended

12 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

0 Months Ended

Dec. 31, 2013

Jan. 31, 2014

Dec. 31, 2013

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 20, 2012

Sep. 11, 2012

Sep. 20, 2012

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Maximum

2.70% Senior Notes Due 2022

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Union Electric Company

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 6.25% Due 2018

6.00% Senior secured notes due 2018

6.00% Senior secured notes due 2018

6.00% Senior secured notes due 2018

6.70% Senior secured notes due 2019

6.70% Senior secured notes due 2019

6.70% Senior secured notes due 2019

5.10% Senior secured notes due 2018

5.10% Senior secured notes due 2018

5.10% Senior secured notes due 2018

5.10% Senior secured notes due 2019

5.10% Senior secured notes due 2019

5.10% Senior secured notes due 2019

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

3.90% Senior secured notes due 2042

Secured Debt

5.10% Senior secured notes due 2018

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Payments of Debt Issuance Costs

'

'

$21,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term debt interest rate

'

'

2.70%

9.75%

9.75%

'

6.25%

6.25%

'

6.00%

6.00%

'

6.70%

6.70%

'

5.10%

5.10%

'

5.10%

5.10%

'

3.90%

'

3.90%

3.90%

'

Amortization of Financing Costs

15,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal Amount Repurchased

'

'

'

87,000,000

'

'

194,000,000

'

'

71,000,000

'

'

121,000,000

'

'

1,000,000

[1]

'

'

56,000,000

'

'

'

'

'

'

'

Premium Plus Accrued and Unpaid Interest

'

'

'

36,000,000

[2]

'

'

47,000,000

[2]

'

'

19,000,000

[3]

'

'

35,000,000

[3]

'

'

'

'

'

12,000,000

[3]

'

'

'

'

'

'

1,000,000

Principal Amount Outstanding After Tender Offer

'

$1,000,000

[4]

$400,000,000

$313,000,000

$313,000,000

[5],[6]

$313,000,000

[5],[6]

$144,000,000

$144,000,000

[5],[6]

$144,000,000

[5],[6]

$179,000,000

$179,000,000

[7],[8]

$179,000,000

[7],[8]

$329,000,000

$329,000,000

[7],[8]

$329,000,000

[7],[8]

$199,000,000

[1]

$199,000,000

[8]

$199,000,000

[8]

$244,000,000

$244,000,000

[8]

$244,000,000

[8]

$485,000,000

[7],[8]

$485,000,000

[7],[8]

$485,000,000

$485,000,000

'

[1]

Amount is less than $1 million.

[2]

Premiums paid in the amount of $21 million in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $400 million 2.70% senior secured notes due 2022. Premiums of $15 million were expensed in 2013 as a result of disallowances in the ICC's December 2013 electric and natural gas rate orders. See Note 2 – Rate and Regulatory Matters for further information regarding the disallowances

[3]

The premiums paid in association with the tender offer were recorded as a regulatory asset and are being amortized over the life of the $485 million 3.90% senior secured notes due 2042.

[4]

These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy.

[5]

Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.

[6]

These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.

[7]

Ameren Missouri has agreed, during the life of these notes, not to optionally redeem, purchase or otherwise retire in full its first mortgage bonds. Ameren Missouri has also agreed to prevent a first mortgage bond release date from occurring as long as any of the 8.45% senior secured notes due 2039 and any of the 3.90% senior secured notes due 2042 remain outstanding.

[8]

These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Missouri first mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the first mortgage bond lien protection associated with these notes to fall away until 2042.

Recovered_Sheet2

Long-Term Debt and Equity Financings (Schedule of Debt Redemptions) (Details) (Ameren Illinois Company, USD $)

Jan. 31, 2014

Dec. 31, 2013

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Aug. 27, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

Jan. 31, 2014

2.70% Senior Notes Due 2022

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Secured Debt

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Subsequent Event

Subsequent Event

Subsequent Event

Subsequent Event

Subsequent Event

Subsequent Event

Subsequent Event

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 9.75% Due 2018

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 6.25% Due 2018

Senior Secured Notes 6.25% Due 2018

Series 1993 5.90% Due 2023

Series 1993 5.90% Due 2023

Series 1994 A 5.70% Due 2024

Series 1994 A 5.70% Due 2024

Series C-1 1993 5.95% Due 2026

Series C-1 1993 5.95% Due 2026

Series C-2 1993 5.70% Due 2026

Series C-2 1993 5.70% Due 2026

Series1998A 5.40% Due 2028

Series1998A 5.40% Due 2028

Series1998B 5.40% Due 2028

Series1998B 5.40% Due 2028

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Environmental Improvement And Pollution Control Revenue Bonds

Series 1993 5.90% Due 2023

Series 1994 A 5.70% Due 2024

Series C-1 1993 5.95% Due 2026

Series C-2 1993 5.70% Due 2026

Series1998A 5.40% Due 2028

Series1998B 5.40% Due 2028

Debt Instrument [Line Items]

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Redemptions of long-term debt

'

'

$87,000,000

'

'

$194,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$163,000,000

$32,000,000

[1]

$36,000,000

[1]

$35,000,000

$8,000,000

$19,000,000

$33,000,000

Debt instrument face amount

$1,000,000

[2]

$400,000,000

$313,000,000

$313,000,000

[3],[4]

$313,000,000

[3],[4]

$144,000,000

$144,000,000

[3],[4]

$144,000,000

[3],[4]

$32,000,000

[5]

$32,000,000

[5]

$36,000,000

[2]

$36,000,000

[2]

$35,000,000

[6]

$35,000,000

[6]

$8,000,000

[6]

$8,000,000

[6]

$19,000,000

[2]

$19,000,000

[2]

$33,000,000

[2]

$33,000,000

[2]

'

'

'

'

'

'

'

[1]

Less than $1 million principal amount of the bonds remain outstanding as of January 31, 2014.

[2]

These bonds are mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture and are secured by substantially all property of the former IP and CIPS. The bonds are callable at 100% of par value. The bonds are also backed by an insurance guarantee policy.

[3]

Ameren Illinois has agreed, during the life of these notes, not to optionally redeem, purchase, or otherwise retire in full its Ameren Illinois mortgage bonds; therefore, an Ameren Illinois first mortgage bond release date will not occur as long as any of these notes are outstanding.

[4]

These notes are collaterally secured by mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any series of first mortgage bonds issued under the Ameren Illinois mortgage indenture remain outstanding. Redemption, purchase, or maturity of all mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the Ameren Illinois mortgage bonds and senior secured notes currently outstanding, and assuming no early retirement of any series of such securities in full, we do not expect the mortgage bond lien protection associated with these notes to fall away until 2028.

[5]

These bonds are first mortgage bonds issued by Ameren Illinois under the CILCO mortgage indenture and are secured by substantially all property of the former CILCO. The bonds are callable at 100% of par value.

[6]

The bonds are callable at 100% of par value.

Recovered_Sheet3

Long-Term Debt and Equity Financings (Schedule of Required and Actual Debt Ratios) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Union Electric Company	'
Debt Instrument [Line Items]	'
Bonds Issuable Based On Coverage Ratio	3,831	[1]
Preferred Stock Issuable Based On Coverage Ratio	2,228
Retired Bond Capacity	729
Union Electric Company | Actual Interest Coverage Ratio	'
Debt Instrument [Line Items]	'
Interest Coverage Ratio	4.5
Dividend Coverage Ratio	116.5
Ameren Illinois Company	'
Debt Instrument [Line Items]	'
Bonds Issuable Based On Coverage Ratio	3,565	[1],[2]
Preferred Stock Issuable Based On Coverage Ratio	203
Retired Bond Capacity	365
Ameren Illinois Company | Actual Interest Coverage Ratio	'
Debt Instrument [Line Items]	'
Interest Coverage Ratio	6.8
Dividend Coverage Ratio	2.4
Minimum | Union Electric Company | Required Dividend Coverage Ratio	'
Debt Instrument [Line Items]	'
Interest Coverage Ratio	2	[3]
Dividend Coverage Ratio	2.5	[4]
Minimum | Ameren Illinois Company | Required Dividend Coverage Ratio	'
Debt Instrument [Line Items]	'
Interest Coverage Ratio	2	[3]
Dividend Coverage Ratio	1.5	[4]
[1]	Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $729 million and $365 million at Ameren Missouri and Ameren Illinois, respectively.
[2]	Amount of bonds issuable by Ameren Illinois based on unfunded property additions and retired bonds solely under the former IP mortgage indenture.
[3]	Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds.
[4]	Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation.

Other_Income_And_Expenses_Othe

Other Income And Expenses (Other Income And Expenses) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Other Nonoperating Income (Expense) [Line Items]	'		'		'
Allowance for equity funds used during construction	$37	[1]	$36	[1]	$34	[1]
Interest income on industrial development revenue bonds	27	[1]	28	[1]	28	[1]
Interest and dividend income	3	[1]	4	[1],[2]	3	[1]
Other	2	[1]	2	[1]	3	[1]
Total miscellaneous income	69	[1]	70	[1]	68	[1]
Donations	12	[1]	24	[1],[3]	8	[1]
Other	14	[1]	13	[1]	15	[1]
Total miscellaneous expense	26	[1]	37	[1]	23	[1]
Union Electric Company	'		'		'
Other Nonoperating Income (Expense) [Line Items]	'		'		'
Allowance for equity funds used during construction	31		31		30
Interest income on industrial development revenue bonds	27		28		28
Interest and dividend income	'		4	[2]	2
Other	'		'		1
Total miscellaneous income	58		63		61
Donations	4		9		3
Other	7		5		7
Total miscellaneous expense	11		14		10
Ameren Illinois Company	'		'		'
Other Nonoperating Income (Expense) [Line Items]	'		'		'
Allowance for equity funds used during construction	6		5		4
Interest and dividend income	2		'		1
Other	2		2		2
Total miscellaneous income	10		7		7
Donations	4		11	[3]	1
Other	5		6		5
Total miscellaneous expense	9		17		6
Illinois Science and Energy Innovation Trust | Ameren Illinois Company	'		'		'
Other Nonoperating Income (Expense) [Line Items]	'		'		'
One-time Donation	$7.50		'		'
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
[2]	Includes interest income received in 2012 relating to a refund of charges included in an expired power purchase agreement with Entergy.
[3]	Includes Ameren Illinois' one-time $7.5 million donation to the Illinois Science and Energy Innovation Trust pursuant to the IEIMA as a result of Ameren Illinois' 2012 participation in the electric delivery formula ratemaking process.

Derivative_Financial_Instrumen2

Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Details)	Dec. 31, 2013		Dec. 31, 2012
	gal		gal
Fuel Oils	'		'
Derivative [Line Items]	'		'
Quantity	66,000,000	[1]	70,000,000	[1]
Natural Gas	'		'
Derivative [Line Items]	'		'
Quantity	136,000,000		147,000,000
Power	'		'
Derivative [Line Items]	'		'
Quantity	14,000,000		25,000,000
Uranium	'		'
Derivative [Line Items]	'		'
Quantity	796,000		446,000
Union Electric Company | Fuel Oils	'		'
Derivative [Line Items]	'		'
Quantity	66,000,000	[1]	70,000,000	[1]
Union Electric Company | Natural Gas	'		'
Derivative [Line Items]	'		'
Quantity	28,000,000		19,000,000
Union Electric Company | Power	'		'
Derivative [Line Items]	'		'
Quantity	3,000,000		11,000,000
Union Electric Company | Uranium	'		'
Derivative [Line Items]	'		'
Quantity	796,000		446,000
Ameren Illinois Company | Natural Gas	'		'
Derivative [Line Items]	'		'
Quantity	108,000,000		128,000,000
Ameren Illinois Company | Power	'		'
Derivative [Line Items]	'		'
Quantity	11,000,000		14,000,000
[1]	Fuel oils consist of heating oil, ultra-low-sulfur diesel, and crude oil.

Derivative_Financial_Instrumen3

Derivative Financial Instruments (Derivative Instruments Carrying Value) (Details) (Not Designated As Hedging Instrument, USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivative [Line Items]	'		'
Derivative assets	$34	[1]	$29	[1]
Derivative liabilities	178	[1]	230	[1]
Fuel Oils | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	6	[1]	8	[1]
Fuel Oils | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	3	[1]	4	[1]
Fuel Oils | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	2	[1]	2	[1]
Fuel Oils | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Fuel Oils | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	1	[1]	2	[1]
Natural Gas | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	2	[1]	1	[1]
Natural Gas | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'		1	[1]
Natural Gas | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	32	[1]	64	[1]
Natural Gas | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Natural Gas | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	25	[1]	45	[1]
Power | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	23	[1]	14	[1]
Power | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'		1	[1]
Power | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	13	[1]	25	[1]
Power | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Power | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	99	[1]	90	[1]
Uranium | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	5	[1]	1	[1]
Uranium | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'
Uranium | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	1	[1]	1	[1]
Union Electric Company	'		'
Derivative [Line Items]	'		'
Derivative assets	33	[1]	28	[1]
Derivative liabilities	24	[1]	25	[1]
Union Electric Company | Fuel Oils | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	6	[1]	8	[1]
Union Electric Company | Fuel Oils | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	3	[1]	4	[1]
Union Electric Company | Fuel Oils | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	2	[1]	2	[1]
Union Electric Company | Fuel Oils | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	1	[1]	2	[1]
Union Electric Company | Natural Gas | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	1	[1]	'	[1]
Union Electric Company | Natural Gas | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'		1	[1]
Union Electric Company | Natural Gas | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	5	[1]	8	[1]
Union Electric Company | Natural Gas | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	6	[1]	7	[1]
Union Electric Company | Power | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	23	[1]	14	[1]
Union Electric Company | Power | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'		1	[1]
Union Electric Company | Power | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	4	[1]	4	[1]
Union Electric Company | Power | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Union Electric Company | Uranium | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	5	[1]	1	[1]
Union Electric Company | Uranium | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	1	[1]	1	[1]
Ameren Illinois Company	'		'
Derivative [Line Items]	'		'
Derivative assets	1	[1]	1	[1]
Derivative liabilities	154	[1]	205	[1]
Ameren Illinois Company | Fuel Oils | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'	[1]	'	[1]
Ameren Illinois Company | Fuel Oils | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'	[1]	'	[1]
Ameren Illinois Company | Fuel Oils | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Ameren Illinois Company | Fuel Oils | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Ameren Illinois Company | Natural Gas | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	1	[1]	1	[1]
Ameren Illinois Company | Natural Gas | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'		'	[1]
Ameren Illinois Company | Natural Gas | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	27	[1]	56	[1]
Ameren Illinois Company | Natural Gas | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Ameren Illinois Company | Natural Gas | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	19	[1]	38	[1]
Ameren Illinois Company | Power | Other current assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'	[1]	'	[1]
Ameren Illinois Company | Power | Other assets	'		'
Derivative [Line Items]	'		'
Derivative assets	'		'	[1]
Ameren Illinois Company | Power | MTM derivative liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	9	[1]	21	[1]
Ameren Illinois Company | Power | Other current liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
Ameren Illinois Company | Power | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	99	[1]	90	[1]
Ameren Illinois Company | Uranium | Other deferred credits and liabilities	'		'
Derivative [Line Items]	'		'
Derivative liabilities	'	[1]	'	[1]
[1]	ncludes derivatives subject to regulatory deferral.

Derivative_Financial_Instrumen4

Derivative Financial Instruments (Cumulative Amount Of Pretax Net Gains (Losses) On All Derivative Instruments In OCI) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	$216		$100
Current losses deferred as regulatory assets	156		247
Power	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	23		'
Current losses deferred as regulatory assets	13		'
Fuel Oils	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	3		'
Current losses deferred as regulatory assets	1		'
Natural Gas	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	2		'
Current losses deferred as regulatory assets	32		'
Uranium	'		'
Derivative [Line Items]	'		'
Current losses deferred as regulatory assets	5		'
Regulatory Liabilities Or Assets | Power	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-89	[1]	-99	[1]
Regulatory Liabilities Or Assets | Fuel Oils	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	2	[2]	4	[2]
Regulatory Liabilities Or Assets | Natural Gas	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-55	[3]	-107	[3]
Regulatory Liabilities Or Assets | Uranium	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-6	[4]	-2	[4]
Union Electric Company	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	57		18
Current losses deferred as regulatory assets	118		163
Union Electric Company | Power	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	23		'
Current losses deferred as regulatory assets	4		'
Union Electric Company | Fuel Oils	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	3		'
Current losses deferred as regulatory assets	1		'
Union Electric Company | Natural Gas	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	1		'
Current losses deferred as regulatory assets	5		'
Union Electric Company | Uranium	'		'
Derivative [Line Items]	'		'
Current losses deferred as regulatory assets	5		'
Union Electric Company | Regulatory Liabilities Or Assets | Power	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	19	[1]	12	[1]
Union Electric Company | Regulatory Liabilities Or Assets | Fuel Oils	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	2	[2]	4	[2]
Union Electric Company | Regulatory Liabilities Or Assets | Natural Gas	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-10	[3]	-14	[3]
Union Electric Company | Regulatory Liabilities Or Assets | Uranium	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-6	[4]	-2	[4]
Ameren Illinois Company	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	159		82
Current losses deferred as regulatory assets	38		84
Ameren Illinois Company | Power	'		'
Derivative [Line Items]	'		'
Current losses deferred as regulatory assets	9		'
Ameren Illinois Company | Natural Gas	'		'
Derivative [Line Items]	'		'
Current gains deferred as regulatory liabilities	1		'
Current losses deferred as regulatory assets	27		'
Ameren Illinois Company | Regulatory Liabilities Or Assets | Power	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-108	[1]	-111	[1]
Ameren Illinois Company | Regulatory Liabilities Or Assets | Fuel Oils	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	'	[2]	'	[2]
Ameren Illinois Company | Regulatory Liabilities Or Assets | Natural Gas	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	-45	[3]	-93	[3]
Ameren Illinois Company | Regulatory Liabilities Or Assets | Uranium	'		'
Derivative [Line Items]	'		'
Cumulative deferred pretax gains (losses)	'	[4]	'	[4]
[1]	Represents net gains (losses) associated with power derivative contracts. These contracts are a partial hedge of power price requirements through May 2032 at Ameren and Ameren Illinois and through December 2015 at Ameren Missouri, in each case as of December 31, 2013. Current gains deferred as regulatory liabilities include $23 million and $23 million at Ameren and Ameren Missouri, respectively, as of December 31, 2013. Current losses deferred as regulatory assets include $13 million, $4 million, and $9 million at Ameren, Ameren Missouri and Ameren Illinois, respectively, as of December 31, 2013.
[2]	Represents net gains on fuel oils derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri’s transportation costs for coal through October 2016, as of December 31, 2013. Current gains deferred as regulatory liabilities include $3 million and $3 million at Ameren and Ameren Missouri as of December 31, 2013, respectively. Current losses deferred as regulatory assets include $1 million and $1 million at Ameren and Ameren Missouri as of December 31, 2013, respectively.
[3]	Represents net losses associated with natural gas derivative contracts. These contracts are a partial hedge of natural gas requirements through October 2019 at Ameren and Ameren Missouri and through March 2017 at Ameren Illinois, in each case as of December 31, 2013. Current gains deferred as regulatory liabilities include $2 million, $1 million, and $1 million at Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2013. Current losses deferred as regulatory assets include $32 million, $5 million, and $27 million at Ameren, Ameren Missouri and Ameren Illinois, respectively, as of December 31, 2013.
[4]	Represents net losses on uranium derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri's uranium requirements through October 2016, as of December 31, 2013. Current losses deferred as regulatory assets include $5 million and $5 million at Ameren and Ameren Missouri as of December 31, 2013, respectively.

Derivative_Financial_Instrumen5

Derivative Financial Instruments Derivative Financial Instruments (Offsetting Derivative Assets and Liabilities) (Details) (Commodity Contract, USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts Recognized in the Balance Sheet	$34	[1]	$29	[1]
Derivative Instruments	10		10
Cash Collateral Received/Posted	'	[2]	'	[2]
Net Amount	24		19
Gross Amounts Recognized in the Balance Sheet	178	[1]	230	[1]
Derivative Instruments	10		10
Cash Collateral Received/Posted	24	[2]	65	[2]
Net Amount	144		155
Union Electric Company	'		'
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts Recognized in the Balance Sheet	33	[1]	28	[1]
Derivative Instruments	9		9
Cash Collateral Received/Posted	'	[2]	'	[2]
Net Amount	24		19
Gross Amounts Recognized in the Balance Sheet	24	[1]	25	[1]
Derivative Instruments	9		9
Cash Collateral Received/Posted	9	[2]	7	[2]
Net Amount	6		9
Ameren Illinois Company	'		'
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts Recognized in the Balance Sheet	1		1
Derivative Instruments	1		1
Cash Collateral Received/Posted	'	[2]	'	[2]
Net Amount	0		0
Gross Amounts Recognized in the Balance Sheet	154	[1]	205	[1]
Derivative Instruments	1		1
Cash Collateral Received/Posted	15	[2]	58	[2]
Net Amount	$138		$146
[1]	The derivative asset and liability balances are presented net of counterparty credit considerations.
[2]	Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” and “Other assets” on the balance sheet.

Derivative_Financial_Instrumen6

Derivative Financial Instruments (Maximum Exposure If Counterparties Fail To Perform On Contracts) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Concentration Risk [Line Items]	'	'
Maximum exposure to counterparties related to derivative contracts	$13	$23
Union Electric Company	'	'
Concentration Risk [Line Items]	'	'
Maximum exposure to counterparties related to derivative contracts	12	22
Ameren Illinois Company	'	'
Concentration Risk [Line Items]	'	'
Maximum exposure to counterparties related to derivative contracts	$1	$1

Derivative_Financial_Instrumen7

Derivative Financial Instruments (Potential Loss On Counterparty Exposures) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Concentration Risk [Line Items]	'	'
Potential loss on counterparty exposures related to derivative contracts	$6	$15
Union Electric Company	'	'
Concentration Risk [Line Items]	'	'
Potential loss on counterparty exposures related to derivative contracts	$6	$15

Derivative_Financial_Instrumen8

Derivative Financial Instruments (Derivative Instruments With Credit Risk-Related Contingent Features) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivative [Line Items]	'		'
Aggregate Fair Value of Derivative Liabilities	$145	[1]	$226	[1]
Cash Collateral Posted	17		61
Potential Aggregate Amount of Additional Collateral Required	122	[2]	155	[2]
Union Electric Company	'		'
Derivative [Line Items]	'		'
Aggregate Fair Value of Derivative Liabilities	70	[1]	78	[1]
Cash Collateral Posted	2		3
Potential Aggregate Amount of Additional Collateral Required	67	[2]	71	[2]
Ameren Illinois Company	'		'
Derivative [Line Items]	'		'
Aggregate Fair Value of Derivative Liabilities	75	[1]	148	[1]
Cash Collateral Posted	15		58
Potential Aggregate Amount of Additional Collateral Required	$55	[2]	$84	[2]
[1]	Prior to consideration of master trading and netting agreements and including NPNS and accrual contract exposures.
[2]	As collateral requirements with certain counterparties are based on master trading and netting agreements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such agreements.

Derivative_Financial_Instrumen9

Derivative Financial Instruments (Cash Flow Hedges) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating revenues	$1,322	$1,638	$1,403	$1,475	$1,258	$1,709	$1,402	$1,412	$5,838	$5,781	$6,148

Recovered_Sheet4

Derivative Financial Instruments (Derivatives That Qualify For Regulatory Deferral) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	$56	[1]	($112)	[1]
Fuel Oils	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	-2		-15
Natural Gas	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	52		84
Power	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	10	[1]	-180	[1]
Uranium	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	-4		-1
Union Electric Company	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	5		-15
Union Electric Company | Fuel Oils	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	-2		-15
Union Electric Company | Natural Gas	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	4		10
Union Electric Company | Power	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	7		-9
Union Electric Company | Uranium	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	-4		-1
Ameren Illinois Company	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	51		103
Ameren Illinois Company | Natural Gas	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	48		74
Ameren Illinois Company | Power	'		'
Derivative [Line Items]	'		'
Gain (Loss) RecognizedIn Regulatory Liabilitiesor Regulatory Assets	$3		$29
[1]	Amounts include intercompany eliminations

Fair_Value_Measurements_Schedu

Fair Value Measurements (Schedule of Valuation Process and Unobservable Inputs) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Discounted Cash Flow | Minimum | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	'		0.21%	[1]
Counterparty credit risk	0.26%	[2],[3]	0.12%	[2],[3]
Credit risk	'		2.00%	[2],[3]
Discounted Cash Flow | Minimum | Power	'		'
Fair Value Inputs [Abstract]	'		'
Counterparty credit risk	0.39%	[2],[3]	0.22%	[2],[3]
Credit risk	2.00%	[2],[3]	2.00%	[2],[3]
Average bid/ask consensus peak and off-peak pricing	25	[3]	22	[3]
Estimated auction price for FTRs	-1,594	[1]	-281	[1]
Nodal basis	-3	[3]	-5	[3]
Discounted Cash Flow | Minimum | Uranium	'		'
Fair Value Inputs [Abstract]	'		'
Average bid/ask consensus pricing	34	[1]	43	[1]
Discounted Cash Flow | Minimum | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	'		0.21%	[1]
Counterparty credit risk	0.26%	[2],[3]	0.12%	[2],[3]
Credit risk	'		2.00%	[2],[3]
Discounted Cash Flow | Minimum | Union Electric Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Counterparty credit risk	0.39%	[2],[3]	0.22%	[2],[3]
Credit risk	2.00%	[2],[3]	2.00%	[2],[3]
Average bid/ask consensus peak and off-peak pricing	25	[3]	24	[3]
Estimated auction price for FTRs	-1,594	[1]	-281	[1]
Nodal basis	-3	[3]	-5	[3]
Discounted Cash Flow | Minimum | Union Electric Company | Uranium	'		'
Fair Value Inputs [Abstract]	'		'
Average bid/ask consensus pricing	34	[1]	43	[1]
Discounted Cash Flow | Minimum | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Credit risk	2.00%	[2],[3]	5.00%	[2],[3]
Nodal basis	-4	[1]	-5	[1]
Average bid/ask consensus pricing	27	[1]	22	[1]
Discounted Cash Flow | Maximum | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	'		0.60%	[1]
Counterparty credit risk	2.00%	[2],[3]	1.00%	[2],[3]
Credit risk	'		2.00%	[2],[3]
Discounted Cash Flow | Maximum | Power	'		'
Fair Value Inputs [Abstract]	'		'
Counterparty credit risk	0.50%	[2],[3]	1.00%	[2],[3]
Credit risk	2.00%	[2],[3]	5.00%	[2],[3]
Average bid/ask consensus peak and off-peak pricing	51	[3]	47	[3]
Estimated auction price for FTRs	945	[1]	1,851	[1]
Nodal basis	-1	[3]	-1	[3]
Discounted Cash Flow | Maximum | Uranium	'		'
Fair Value Inputs [Abstract]	'		'
Average bid/ask consensus pricing	41	[1]	46	[1]
Discounted Cash Flow | Maximum | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	'		0.60%	[1]
Counterparty credit risk	2.00%	[2],[3]	1.00%	[2],[3]
Credit risk	'		2.00%	[2],[3]
Discounted Cash Flow | Maximum | Union Electric Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Counterparty credit risk	0.50%	[2],[3]	1.00%	[2],[3]
Credit risk	2.00%	[2],[3]	2.00%	[2],[3]
Average bid/ask consensus peak and off-peak pricing	51	[3]	56	[3]
Estimated auction price for FTRs	945	[1]	1,851	[1]
Nodal basis	-1	[3]	-1	[3]
Discounted Cash Flow | Maximum | Union Electric Company | Uranium	'		'
Fair Value Inputs [Abstract]	'		'
Average bid/ask consensus pricing	41	[1]	46	[1]
Discounted Cash Flow | Maximum | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Credit risk	2.00%	[2],[3]	5.00%	[2],[3]
Nodal basis	0	[1]	-1	[1]
Average bid/ask consensus pricing	36	[1]	47	[1]
Discounted Cash Flow | Weighted Average | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	'		0.44%	[1]
Counterparty credit risk	1.00%	[2],[3]	1.00%	[2],[3]
Credit risk	'		2.00%	[2],[3]
Discounted Cash Flow | Weighted Average | Power	'		'
Fair Value Inputs [Abstract]	'		'
Counterparty credit risk	0.42%	[2],[3]	1.00%	[2],[3]
Credit risk	2.00%	[2],[3]	5.00%	[2],[3]
Average bid/ask consensus peak and off-peak pricing	32	[3]	31	[3]
Estimated auction price for FTRs	305	[1]	178	[1]
Nodal basis	-2	[3]	-3	[3]
Discounted Cash Flow | Weighted Average | Uranium	'		'
Fair Value Inputs [Abstract]	'		'
Average bid/ask consensus pricing	36	[1]	44	[1]
Discounted Cash Flow | Weighted Average | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	'		0.44%	[1]
Counterparty credit risk	1.00%	[2],[3]	1.00%	[2],[3]
Credit risk	'		2.00%	[2],[3]
Discounted Cash Flow | Weighted Average | Union Electric Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Counterparty credit risk	0.42%	[2],[3]	1.00%	[2],[3]
Credit risk	2.00%	[2],[3]	2.00%	[2],[3]
Average bid/ask consensus peak and off-peak pricing	40	[3]	36	[3]
Estimated auction price for FTRs	305	[1]	178	[1]
Nodal basis	-2	[3]	-2	[3]
Discounted Cash Flow | Weighted Average | Union Electric Company | Uranium	'		'
Fair Value Inputs [Abstract]	'		'
Average bid/ask consensus pricing	36	[1]	44	[1]
Discounted Cash Flow | Weighted Average | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Credit risk	2.00%	[2],[3]	5.00%	[2],[3]
Nodal basis	-2	[1]	-3	[1]
Average bid/ask consensus pricing	30	[1]	30	[1]
Option Model | Minimum | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Volatilities	10.00%	[1]	7.00%	[1]
Option Model | Minimum | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Volatilities	10.00%	[1]	7.00%	[1]
Option Model | Maximum | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Volatilities	35.00%	[1]	27.00%	[1]
Option Model | Maximum | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Volatilities	35.00%	[1]	27.00%	[1]
Option Model | Weighted Average | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Volatilities	16.00%	[1]	24.00%	[1]
Option Model | Weighted Average | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs [Abstract]	'		'
Volatilities	16.00%	[1]	24.00%	[1]
Fundamental Energy Production Model | Minimum | Power	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	3.00%	[1],[4]	'
Estimated future gas prices	4	[1]	4	[1]
Fundamental Energy Production Model | Minimum | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	3.00%	[1],[4]	'
Estimated future gas prices	4	[1]	4	[1]
Fundamental Energy Production Model | Maximum | Power	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	4.00%	[1],[4]	'
Estimated future gas prices	5	[1]	8	[1]
Fundamental Energy Production Model | Maximum | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	4.00%	[1],[4]	'
Estimated future gas prices	5	[1]	8	[1]
Fundamental Energy Production Model | Weighted Average | Power	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	4.00%	[1],[4]	'
Estimated future gas prices	5	[1]	6	[1]
Fundamental Energy Production Model | Weighted Average | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Escalation rate	4.00%	[1],[4]	'
Estimated future gas prices	5	[1]	6	[1]
Contract Price Allocation | Minimum | Power	'		'
Fair Value Inputs [Abstract]	'		'
Estimated renewable energy credit costs	5	[1]	5	[1]
Contract Price Allocation | Minimum | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Estimated renewable energy credit costs	5	[1]	5	[1]
Contract Price Allocation | Maximum | Power	'		'
Fair Value Inputs [Abstract]	'		'
Estimated renewable energy credit costs	7	[1]	7	[1]
Contract Price Allocation | Maximum | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Estimated renewable energy credit costs	7	[1]	7	[1]
Contract Price Allocation | Weighted Average | Power	'		'
Fair Value Inputs [Abstract]	'		'
Estimated renewable energy credit costs	6	[1]	6	[1]
Contract Price Allocation | Weighted Average | Ameren Illinois Company | Power	'		'
Fair Value Inputs [Abstract]	'		'
Estimated renewable energy credit costs	6	[1]	6	[1]
Derivative liabilities | Fuel Oils	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-3	[5]	-3	[5]
Derivative liabilities | Power	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-110	[5],[6]	-114	[5],[6]
Derivative liabilities | Uranium	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-6	[5]	-2	[5]
Derivative liabilities | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-3	[5]	-3	[5]
Derivative liabilities | Union Electric Company | Power	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-2	[5],[6]	-3	[5],[6]
Derivative liabilities | Union Electric Company | Uranium	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-6	[5]	-2	[5]
Derivative liabilities | Ameren Illinois Company | Power	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative liabilities	-108	[5],[6]	-111	[5],[6]
Derivative assets | Fuel Oils	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	8	[5]	8	[5]
Derivative assets | Power	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	21	[5],[6]	14	[5],[6]
Derivative assets | Uranium	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	'	[5]	'	[5]
Derivative assets | Union Electric Company | Fuel Oils	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	8	[5]	8	[5]
Derivative assets | Union Electric Company | Power	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	21	[5],[6]	14	[5],[6]
Derivative assets | Union Electric Company | Uranium	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	'	[5]	'	[5]
Derivative assets | Ameren Illinois Company | Power	'		'
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]	'		'
Derivative assets	'	[5],[6]	'	[5],[6]
[1]	Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.
[2]	Counterparty credit risk is applied only to counterparties with derivative asset balances. Ameren, Ameren Missouri and Ameren Illinois credit risk is applied only to counterparties with derivative liability balances.
[3]	Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.
[4]	Escalation rate applies to power prices 2026 and beyond.
[5]	The derivative asset and liability balances are presented net of counterparty credit considerations.
[6]	Power valuations use visible third-party pricing evaluated by month for peak and off-peak demand through 2017. Valuations beyond 2017 use fundamentally modeled pricing by month for peak and off-peak demand.

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Counterparty default risk liability valuation adjustment related to derivative contracts	$3	$7
Union Electric Company	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Counterparty default risk liability valuation adjustment related to derivative contracts	1	1
Ameren Illinois Company	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Counterparty default risk liability valuation adjustment related to derivative contracts	$3	$7

Fair_Value_Measurements_Schedu1

Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	$494		$406	[1]
Assets	528		435
Excluded receivables, payables, and accrued income, net	'		2
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	335		265
Assets	336		269
Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	159		141
Assets	163		144
Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Assets	29		22
Cash And Cash Equivalents	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	3		1
Cash And Cash Equivalents | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	3		1
Cash And Cash Equivalents | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Cash And Cash Equivalents | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Commodity Contract	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	34	[2]	29	[2]
Derivative liabilities	178	[2]	230	[2]
Commodity Contract | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	4	[2]
Derivative liabilities	3	[2]	8	[2]
Commodity Contract | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	4	[2]	3	[2]
Derivative liabilities	56	[2]	103	[2]
Commodity Contract | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	29	[2]	22	[2]
Derivative liabilities	119	[2]	119	[2]
Commodity Contract | Fuel Oils	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	9	[2]	12	[2]
Derivative liabilities	3	[2]	4	[2]
Commodity Contract | Fuel Oils | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	4	[2]
Derivative liabilities	'	[2]	1	[2]
Commodity Contract | Fuel Oils | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Commodity Contract | Fuel Oils | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	8	[2]	8	[2]
Derivative liabilities	3	[2]	3	[2]
Commodity Contract | Natural Gas	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	2	[2]	2	[2]
Derivative liabilities	57	[2]	109	[2]
Commodity Contract | Natural Gas | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	3	[2]	7	[2]
Commodity Contract | Natural Gas | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	2	[2]	2	[2]
Derivative liabilities	54	[2]	102	[2]
Commodity Contract | Natural Gas | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Commodity Contract | Power	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	23	[2]	15	[2]
Derivative liabilities	112	[2]	115	[2]
Commodity Contract | Power | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Commodity Contract | Power | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	2	[2]	1	[2]
Derivative liabilities	2	[2]	1	[2]
Commodity Contract | Power | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	21	[2]	14	[2]
Derivative liabilities	110	[2]	114	[2]
Commodity Contract | Uranium	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	6	[2]	2	[2]
Commodity Contract | Uranium | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Commodity Contract | Uranium | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Commodity Contract | Uranium | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	6	[2]	2	[2]
Equity Securities | U.S. Large Capitalization	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	332		264
Equity Securities | U.S. Large Capitalization | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	332		264
Equity Securities | U.S. Large Capitalization | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Equity Securities | U.S. Large Capitalization | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Corporate Bonds	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	52		47
Debt Securities | Corporate Bonds | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Corporate Bonds | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	52		47
Debt Securities | Corporate Bonds | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Municipal Bonds	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	2		1
Debt Securities | Municipal Bonds | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Municipal Bonds | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	2		1
Debt Securities | Municipal Bonds | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | U.S. treasury and agency securities	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	94		81
Debt Securities | U.S. treasury and agency securities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | U.S. treasury and agency securities | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	94		81
Debt Securities | U.S. treasury and agency securities | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Asset-Backed Securities	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	10		11
Debt Securities | Asset-Backed Securities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Asset-Backed Securities | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	10		11
Debt Securities | Asset-Backed Securities | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Other debt securities	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	1		1
Debt Securities | Other debt securities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Debt Securities | Other debt securities | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	1		1
Debt Securities | Other debt securities | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	494		406	[1]
Assets	527		434
Union Electric Company | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	335		265
Assets	336		269
Union Electric Company | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	159		141
Assets	162		143
Union Electric Company | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Assets	29		22
Union Electric Company | Cash And Cash Equivalents	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	3		1
Union Electric Company | Cash And Cash Equivalents | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	3		1
Union Electric Company | Cash And Cash Equivalents | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Cash And Cash Equivalents | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Commodity Contract	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	33	[2]	28	[2]
Derivative liabilities	24	[2]	25	[2]
Union Electric Company | Commodity Contract | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	4	[2]
Derivative liabilities	3	[2]	8	[2]
Union Electric Company | Commodity Contract | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	3	[2]	2	[2]
Derivative liabilities	10	[2]	9	[2]
Union Electric Company | Commodity Contract | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	29	[2]	22	[2]
Derivative liabilities	11	[2]	8	[2]
Union Electric Company | Commodity Contract | Fuel Oils	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	9	[2]	12	[2]
Derivative liabilities	3	[2]	4	[2]
Union Electric Company | Commodity Contract | Fuel Oils | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	4	[2]
Derivative liabilities	'	[2]	1	[2]
Union Electric Company | Commodity Contract | Fuel Oils | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Union Electric Company | Commodity Contract | Fuel Oils | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	8	[2]	8	[2]
Derivative liabilities	3	[2]	3	[2]
Union Electric Company | Commodity Contract | Natural Gas	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	1	[2]
Derivative liabilities	11	[2]	15	[2]
Union Electric Company | Commodity Contract | Natural Gas | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	3	[2]	7	[2]
Union Electric Company | Commodity Contract | Natural Gas | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	1	[2]
Derivative liabilities	8	[2]	8	[2]
Union Electric Company | Commodity Contract | Natural Gas | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Union Electric Company | Commodity Contract | Power	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	23	[2]	15	[2]
Derivative liabilities	4	[2]	4	[2]
Union Electric Company | Commodity Contract | Power | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Union Electric Company | Commodity Contract | Power | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	2	[2]	1	[2]
Derivative liabilities	2	[2]	1	[2]
Union Electric Company | Commodity Contract | Power | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	21	[2]	14	[2]
Derivative liabilities	2	[2]	3	[2]
Union Electric Company | Commodity Contract | Uranium	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	6	[2]	2	[2]
Union Electric Company | Commodity Contract | Uranium | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Union Electric Company | Commodity Contract | Uranium | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Union Electric Company | Commodity Contract | Uranium | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	6	[2]	2	[2]
Union Electric Company | Equity Securities | U.S. Large Capitalization	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	332		264
Union Electric Company | Equity Securities | U.S. Large Capitalization | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	332		264
Union Electric Company | Equity Securities | U.S. Large Capitalization | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Equity Securities | U.S. Large Capitalization | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Corporate Bonds	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	52		47
Union Electric Company | Debt Securities | Corporate Bonds | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Corporate Bonds | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	52		47
Union Electric Company | Debt Securities | Corporate Bonds | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Municipal Bonds	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	2		1
Union Electric Company | Debt Securities | Municipal Bonds | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Municipal Bonds | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	2		1
Union Electric Company | Debt Securities | Municipal Bonds | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | U.S. treasury and agency securities	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	94		81
Union Electric Company | Debt Securities | U.S. treasury and agency securities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | U.S. treasury and agency securities | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	94		81
Union Electric Company | Debt Securities | U.S. treasury and agency securities | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Asset-Backed Securities	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	10		11
Union Electric Company | Debt Securities | Asset-Backed Securities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Asset-Backed Securities | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	10		11
Union Electric Company | Debt Securities | Asset-Backed Securities | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Other debt securities	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	1		1
Union Electric Company | Debt Securities | Other debt securities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Union Electric Company | Debt Securities | Other debt securities | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	1		1
Union Electric Company | Debt Securities | Other debt securities | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Nuclear Decommissioning Trust Fund	'		'
Ameren Illinois Company | Commodity Contract	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1		1
Derivative liabilities	154	[2]	205	[2]
Ameren Illinois Company | Commodity Contract | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Ameren Illinois Company | Commodity Contract | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	46	[2]	94	[2]
Ameren Illinois Company | Commodity Contract | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	108	[2]	111	[2]
Ameren Illinois Company | Commodity Contract | Natural Gas	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	1	[2]
Derivative liabilities	46	[2]	94	[2]
Ameren Illinois Company | Commodity Contract | Natural Gas | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Ameren Illinois Company | Commodity Contract | Natural Gas | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	1	[2]	1	[2]
Derivative liabilities	46	[2]	94	[2]
Ameren Illinois Company | Commodity Contract | Natural Gas | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative assets	'	[2]	'	[2]
Derivative liabilities	'	[2]	'	[2]
Ameren Illinois Company | Commodity Contract | Power	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	108	[2]	111	[2]
Ameren Illinois Company | Commodity Contract | Power | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Ameren Illinois Company | Commodity Contract | Power | Significant Other Observable Inputs (Level 2)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	'	[2]	'	[2]
Ameren Illinois Company | Commodity Contract | Power | Significant Other Unobservable Inputs (Level 3)	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Derivative liabilities	$108	[2]	$111	[2]
[1]	Balance excludes $2 million of receivables, payables, and accrued income, net.
[2]	The derivative asset and liability balances are presented net of counterparty credit considerations.

Fair_Value_Measurements_Schedu2

Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fuel Oils	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	$5		$3
Included in regulatory assets/liabilities	'		-1
Total realized and unrealized gains (losses)	0		-1
Purchases	3		7
Sales	-1		-3
Settlements	-2		-2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	'		1
Ending balance	5		5
Change in unrealized gains (losses) related to assets/liabilities still held	0		-1
Natural Gas	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	0		-174
Included in regulatory assets/liabilities	-1		-27
Total realized and unrealized gains (losses)	-1		-27
Purchases	1		'
Settlements	'		16
Transfers out of Level 3	'		185
Ending balance	0		0
Change in unrealized gains (losses) related to assets/liabilities still held	0		0
Power	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	-100	[1]	81	[1]
Included in regulatory assets/liabilities	-15		-175	[1]
Total realized and unrealized gains (losses)	-15		-175	[1]
Purchases	40		21	[1]
Sales	'		-1	[1]
Settlements	-15		-22	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	-3		'
Transfers out of Level 3	4		-4	[1]
Ending balance	-89		-100	[1]
Change in unrealized gains (losses) related to assets/liabilities still held	-25		-175
Uranium	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	-2		-1
Included in regulatory assets/liabilities	-3		-2
Total realized and unrealized gains (losses)	-3		-2
Purchases	-2		'
Settlements	1		1
Ending balance	-6		-2
Change in unrealized gains (losses) related to assets/liabilities still held	-2		-1
Union Electric Company | Fuel Oils	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	5		3
Included in regulatory assets/liabilities	'		-1
Total realized and unrealized gains (losses)	0		-1
Purchases	3		7
Sales	-1		-3
Settlements	-2		-2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	'		1
Ending balance	5		5
Change in unrealized gains (losses) related to assets/liabilities still held	0		-1
Union Electric Company | Natural Gas	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	0		-14
Included in regulatory assets/liabilities	'		-2
Total realized and unrealized gains (losses)	'		-2
Purchases	'		'
Settlements	'		1
Transfers out of Level 3	'		15
Ending balance	0		0
Change in unrealized gains (losses) related to assets/liabilities still held	0		0
Union Electric Company | Power	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	11		21
Included in regulatory assets/liabilities	3		11
Total realized and unrealized gains (losses)	3		11
Purchases	40		21
Sales	'		-1
Settlements	-36		-37
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3	-3		'
Transfers out of Level 3	4		-4
Ending balance	19		11
Change in unrealized gains (losses) related to assets/liabilities still held	-1		0
Union Electric Company | Uranium	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	-2		-1
Included in regulatory assets/liabilities	-3		-2
Total realized and unrealized gains (losses)	-3		-2
Purchases	-2		'
Settlements	1		1
Ending balance	-6		-2
Change in unrealized gains (losses) related to assets/liabilities still held	-2		-1
Ameren Illinois Company | Natural Gas	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	0		-160
Included in regulatory assets/liabilities	-1		-25
Total realized and unrealized gains (losses)	-1		-25
Purchases	1		'
Settlements	'		15
Transfers out of Level 3	'		170
Ending balance	0		0
Change in unrealized gains (losses) related to assets/liabilities still held	0		0
Ameren Illinois Company | Power	'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'
Beginning balance	-111		-140
Included in regulatory assets/liabilities	-18		-226
Total realized and unrealized gains (losses)	-18		-226
Purchases	'		'
Sales	'		'
Settlements	21		255
Transfers out of Level 3	'		'
Ending balance	-108		-111
Change in unrealized gains (losses) related to assets/liabilities still held	($24)		($191)	[2]
[1]	Ameren amounts include intercompany eliminations.
[2]	The change in unrealized losses was due to decreases in long-term power prices applied to 20-year Ameren Illinois swap contracts, which expire in May 2032.

Fair_Value_Measurements_Schedu3

Fair Value Measurements (Schedule Of Transfers Between Fair Value Hierarchy Levels) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Net fair value of Level 3 transfers	$1	$182
Fuel Oils	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfers into Level 3/Transfers out of Level 1	'	1
Natural Gas	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfers out of Level 3/Transfers into Level 2	'	185
Power	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfer into Level 3/Transfers out of Level 2	-3	'
Transfers out of Level 3/Transfers into Level 2	4	-4
Union Electric Company	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Net fair value of Level 3 transfers	1	12
Union Electric Company | Fuel Oils	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfers into Level 3/Transfers out of Level 1	'	1
Union Electric Company | Natural Gas	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfers out of Level 3/Transfers into Level 2	'	15
Union Electric Company | Power	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfer into Level 3/Transfers out of Level 2	-3	'
Transfers out of Level 3/Transfers into Level 2	4	-4
Ameren Illinois Company | Natural Gas	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Transfers out of Level 3/Transfers into Level 2	'	$170

Fair_Value_Measurements_Schedu4

Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Long-term Debt and Capital Lease Obligations	$6,038	[1]	$6,157	[1]
Preferred stock	142	[1]	142	[1]
Fair Value	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Long-term debt and capital lease obligations (including current portion)	6,584	[1]	7,110	[1]
Preferred stock	118	[1]	123	[1]
Union Electric Company | Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Long-term Debt and Capital Lease Obligations	3,757		4,006
Preferred stock	80		80
Union Electric Company | Fair Value	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Long-term debt and capital lease obligations (including current portion)	4,124		4,625
Preferred stock	71		74
Ameren Illinois Company | Carrying Amount	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Long-term Debt and Capital Lease Obligations	1,856		1,727
Preferred stock	62		62
Ameren Illinois Company | Fair Value	'		'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'		'
Long-term debt and capital lease obligations (including current portion)	2,028		2,020
Preferred stock	$47		$49
[1]	Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.

Nuclear_Decommissioning_Trust_2

Nuclear Decommissioning Trust Fund Investments (Proceeds From The Sale Of Investments And Related Gross Realized Gains And Losses In Nuclear Decommissioning Trust Fund) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'	'
Sales and maturities of securities - nuclear decommissioning trust fund	$196	$384	$199
Gross realized gains	7	6	5
Gross realized losses	5	2	4
Minimum | Nuclear Decommissioning Trust Fund	'	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'	'
Trust fund investments, target allocation percentage	60.00%	'	'
Maximum | Nuclear Decommissioning Trust Fund	'	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'	'
Trust fund investments, target allocation percentage	70.00%	'	'
Union Electric Company	'	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'	'
Sales and maturities of securities - nuclear decommissioning trust fund	$196	$384	$199

Nuclear_Decommissioning_Trust_3

Nuclear Decommissioning Trust Fund Investments (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'
Cost	$297,000,000	$281,000,000
Gross unrealized gains	203,000,000	138,000,000
Gross unrealized loss	6,000,000	11,000,000
Fair Value	494,000,000	408,000,000
Debt Securities	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'
Cost	157,000,000	133,000,000
Gross unrealized gains	4,000,000	8,000,000
Gross unrealized loss	2,000,000	'
Fair Value	159,000,000	141,000,000
Equity Securities	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'
Cost	137,000,000	145,000,000
Gross unrealized gains	199,000,000	130,000,000
Gross unrealized loss	4,000,000	11,000,000
Fair Value	332,000,000	264,000,000
Cash	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'
Cost	3,000,000	1,000,000
Fair Value	3,000,000	1,000,000
Other Debt And Equity Securities	'	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'	'
Cost	'	2,000,000	[1]
Fair Value	'	$2,000,000	[1]
[1]	Represents payables relating to pending security purchases, net of receivables related to pending security sales and interest receivables.

Nuclear_Decommissioning_Trust_4

Nuclear Decommissioning Trust Fund Investments (Costs And Fair Values Of Investments In Debt Securities In Nuclear Decommissioning Trust Fund According To Contractual Maturities) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Investments, Debt and Equity Securities [Abstract]	'
Cost, Less than 5 years	$93
Cost, 5 years to 10 years	31
Cost, Due after 10 years	33
Cost, Total	157
Fair Value, Less than 5 years	94
Fair Value, 5 years to 10 years	32
Fair Value, Due after 10 years	33
Fair Value, Total	$159

Nuclear_Decommissioning_Trust_5

Nuclear Decommissioning Trust Fund Investments (Fair Value And The Gross Unrealized Losses Of The Available-For-Sale Securities Held In Nuclear Decommissioning Trust Fund) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Nuclear Decommissioning Trust Fund Investments [Line Items]	'
Less than 12 months, fair value	$78
Less than 12 months, gross unrealized losses	2
12 months or greater, fair value	7
12 months or greater, gross unrealized losses	4
Total, fair value	85
Total, gross unrealized losses	6
Debt Securities	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'
Less than 12 months, fair value	72
Less than 12 months, gross unrealized losses	2
Total, fair value	72
Total, gross unrealized losses	2
Equity Securities	'
Nuclear Decommissioning Trust Fund Investments [Line Items]	'
Less than 12 months, fair value	6
12 months or greater, fair value	7
12 months or greater, gross unrealized losses	4
Total, fair value	13
Total, gross unrealized losses	$4

Callaway_Energy_Center_Details

Callaway Energy Center (Details) (USD $)	12 Months Ended							12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2013	Mar. 30, 2014
	mill				Reduction To Depreciation And Amortization	Reduction To Other Operations And Maintenance	Reduction In Property And Plant	Nuclear Plant	Nuclear Plant
Loss Contingencies [Line Items]	'	'	'	'	'	'	'	'	'
Nwf Fee Number Of Mills	1	'	'	'	'	'	'	'	'
Settlement payment	'	'	'	$11	$2	$2	$1	$6	'
Gain Contingency, Unrecorded Amount	'	'	'	'	'	'	'	'	15
Useful life	'	'	'	'	'	'	'	'40 years	'
Annual decommissioning costs included in costs of service	'	$7	$7	'	'	'	'	$7	'
MoPSC requirement to file updated cost study and funding analysis for decommissioning Callaway energy center	'3 years	'	'	'	'	'	'	'	'

Retirement_Benefits_Narrative_

Retirement Benefits (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
	bond
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation, Change in Discount Rate	0.75%		'
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	$19	[1],[2]	'
Defined Benefit Plan, Funded Status of Plan	461	[3]	1,143	[3]
Number of high-quality corporate bonds	500		'
Defined benefit plan, estimated future employer contributions during the next five years	270		'
Actual return in excess of (or less than) expected return, percentage	25.00%		'
Expected return on plan assets, period	'4 years		'
Amortization basis, straight line, in years	'10 years		'
Pension Benefits	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	12	[2]	'
Defined Benefit Plan, Funded Status of Plan	-439	[3]	-924	[3]
Assumptions used calculating net periodic benefit cost, expected long-term return on assets in 2013	7.25%		'
Postretirement Benefits	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	7	[2]	'
Defined Benefit Plan, Funded Status of Plan	-22	[3]	-219	[3]
Assumptions used calculating net periodic benefit cost, expected long-term return on assets in 2013	7.00%		'
Minimum	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined benefit plan, estimated future employer contributions during the next five years	20		'
Maximum	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined benefit plan, estimated future employer contributions during the next five years	100		'
Private equity	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Number of limited partnerships in private equity funds	9		'
Minimum invested capital within limited partnership investments	0.1		'
Maximum invested capital within limited partnership investments	$5		'
Union Electric Company | Pension Benefits	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Future funding requirement, percentage	52.00%		'
Ameren Illinois Company | Pension Benefits	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Future funding requirement, percentage	47.00%		'
[1]	(b)The net periodic benefit cost includes a $6 million and a $7 million net gain for pension benefits and postretirement benefits, respectively, which was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). This net gain includes the curtailment gain recognized in 2013 as a result of a significant reduction in employees as of the December 2, 2013 closing date of the New AER divestiture. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.
[2]	Includes amounts for Ameren registrant and nonregistrant subsidiaries
[3]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Retirement_Benefits_Summary_Of

Retirement Benefits (Summary Of Benefit Liability Recorded) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]	'		'
Benefit liability recorded on the balance sheet	$461	[1]	$1,143	[1]
Union Electric Company	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Benefit liability recorded on the balance sheet	191		464
Ameren Illinois Company	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Benefit liability recorded on the balance sheet	$198		$408
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Retirement_Benefits_Funded_Sta

Retirement Benefits (Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Change in plan assets:	'		'		'
Funded status – deficiency	($461)	[1]	($1,143)	[1]	'
Amounts recognized in the balance sheet consist of:	'		'		'
Noncurrent liability	466		1,138		'
Net liability recognized	461	[1]	1,143	[1]	'
Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Accumulated benefit obligation at end of year	3,698	[1]	3,829	[1]	'
Change in benefit obligation:	'		'		'
Net benefit obligation at beginning of year	4,051	[1]	3,764	[1]	'
Service cost	91	[1],[2]	81	[1],[2]	73	[2]
Interest cost	163	[1],[2]	166	[1],[2]	175	[2]
Participant contributions	'	[1]	'	[1]	'
Actuarial (gain) loss	-207	[1]	240	[1]	'
Curtailment gain(c)	'	[2],[3]	'	[2],[3]	'
Settlement	'	[1],[4]	'	[5]	'
Benefits paid	-198	[1]	-200	[1]	'
Net benefit obligation at end of year	3,900	[1]	4,051	[1]	3,764	[1]
Change in plan assets:	'		'		'
Fair value of plan assets at beginning of year	3,127	[1]	2,814	[1]	'
Actual return on plan assets	376	[1]	385	[1]	'
Employer contributions	156	[1]	128	[1]	96	[1]
Participant contributions	'	[1]	'	[1]	'
Benefits paid	-198	[1]	-200	[1]	'
Fair value of plan assets at end of year	3,461	[1]	3,127	[1]	2,814	[1]
Funded status – deficiency	439	[1]	924	[1]	'
Accrued benefit cost at December 31	439	[1]	924	[1]	'
Amounts recognized in the balance sheet consist of:	'		'		'
Noncurrent asset	'		'		'
Current liability(f)	3	[1],[6]	3	[1],[6]	'
Noncurrent liability	436	[1]	921	[1]	'
Net liability recognized	439	[1]	924	[1]	'
Amounts recognized in regulatory assets consist of:	'		'		'
Net actuarial (gain) loss	282	[1]	699	[1]	'
Prior service cost (credit)	-7	[1]	-6	[1]	'
Amounts (pretax) recognized in accumulated OCI consist of:	'		'		'
Net actuarial (gain) loss	17	[1]	65	[1]	'
Prior service cost (credit)	'	[1]	-14	[1]	'
Total	292	[1]	744	[1]	'
Postretirement Benefits	'		'		'
Change in benefit obligation:	'		'		'
Net benefit obligation at beginning of year	1,157	[1]	1,145	[1]	'
Service cost	22	[1],[2]	22	[1],[2]	20	[2]
Interest cost	46	[1],[2]	47	[1],[2]	54	[2]
Participant contributions	16	[1]	16	[1]	'
Actuarial (gain) loss	-76	[1]	-10	[1]	'
Curtailment gain(c)	-3	[2],[3]	'	[2],[3]	'
Settlement	5	[1],[4]	'	[5]	'
Benefits paid	-64	[1]	-69	[1]	'
Early retiree reinsurance program receipt	'	[1]	2	[1]	'
Federal subsidy on benefits paid	3	[1]	4	[1]	'
Net benefit obligation at end of year	1,096	[1]	1,157	[1]	1,145	[1]
Change in plan assets:	'		'		'
Fair value of plan assets at beginning of year	938	[1]	836	[1]	'
Actual return on plan assets	156	[1]	104	[1]	'
Employer contributions	25	[1]	45	[1]	129	[1]
Federal subsidy on benefits paid	3	[1]	4	[1]	'
Early retiree reinsurance program receipt	'	[1]	2	[1]	'
Participant contributions	16	[1]	16	[1]	'
Benefits paid	-64	[1]	-69	[1]	'
Fair value of plan assets at end of year	1,074	[1]	938	[1]	836	[1]
Funded status – deficiency	22	[1]	219	[1]	'
Accrued benefit cost at December 31	22	[1]	219	[1]	'
Amounts recognized in the balance sheet consist of:	'		'		'
Noncurrent asset	9	[1],[7]	'		'
Current liability(f)	1	[1],[6]	2	[1],[6]	'
Noncurrent liability	30	[1]	217	[1]	'
Net liability recognized	22	[1]	219	[1]	'
Amounts recognized in regulatory assets consist of:	'		'		'
Net actuarial (gain) loss	-71	[1]	103	[1]	'
Prior service cost (credit)	-20	[1]	-24	[1]	'
Amounts (pretax) recognized in accumulated OCI consist of:	'		'		'
Net actuarial (gain) loss	-12	[1]	5	[1]	'
Prior service cost (credit)	-1	[1]	-6	[1]	'
Total	($104)	[1]	$78	[1]	'
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
[2]	Includes amounts for Ameren registrant and nonregistrant subsidiaries
[3]	Effective with the divestiture of New AER on December 2, 2013, the liability for active management employees of New AER and its subsidiaries not eligible to retire were neither transferred to IPH nor retained by Ameren, which resulted in a curtailment gain. See Note 16 – Divestiture Transactions and Discontinued Operations for further information on the divestiture.
[4]	Effective with the divestiture of New AER on December 2, 2013, the liability for active union employees of New AER and its subsidiaries not eligible to retire was transferred to IPH based on the assumption of the collective bargaining agreements in place, which resulted in a settlement. See Note 16 – Divestiture Transactions and Discontinued Operations for further information on the divestiture.
[5]	Not applicable.
[6]	Included in "Other current liabilities" on Ameren's consolidated balance sheet.
[7]	Included in "Other assets" on Ameren's consolidated balance sheet.

Retirement_Benefits_Assumption

Retirement Benefits (Assumptions Used To Determine Benefit Obligations) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Discount rate at measurement date	4.75%	4.00%
Increase in future compensation	3.50%	3.50%
Medical cost trend rate (initial)	'	'
Medical cost trend rate (ultimate)	'	'
Postretirement Benefits	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Discount rate at measurement date	4.75%	4.00%
Increase in future compensation	3.50%	3.50%
Medical cost trend rate (initial)	5.00%	5.00%
Medical cost trend rate (ultimate)	5.00%	5.00%

Retirement_Benefits_Cash_Contr

Retirement Benefits (Cash Contributions Made To Benefit Plans) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	$156	[1]	$128	[1]	$96	[1]
Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	25	[1]	45	[1]	129	[1]
Union Electric Company | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	60		52		43
Union Electric Company | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	10		9		9
Ameren Illinois Company | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	50		46		28
Ameren Illinois Company | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	11		35		118
Other | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	46		30		25
Other | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Cash contributions to benefit plans	$4		$1		$2
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Retirement_Benefits_Target_All

Retirement Benefits (Target Allocation Of The Plans' Asset Categories) (Details)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Pension Benefits	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%		100.00%
Pension Benefits | Cash And Cash Equivalents	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	0.00%		'
Maximum Target Allocation	5.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	2.00%		2.00%
Pension Benefits | Equity Securities	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	50.00%		'
Maximum Target Allocation	60.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	58.00%		54.00%
Pension Benefits | U.S. large capitalization	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	29.00%		'
Maximum Target Allocation	39.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	36.00%		34.00%
Pension Benefits | U.S. small and mid-capitalization	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	2.00%		'
Maximum Target Allocation	12.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	8.00%		7.00%
Pension Benefits | International and emerging markets	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	9.00%		'
Maximum Target Allocation	19.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	14.00%		13.00%
Pension Benefits | Debt Securities	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	35.00%		'
Maximum Target Allocation	45.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	36.00%		39.00%
Pension Benefits | Real estate	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	0.00%		'
Maximum Target Allocation	9.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	4.00%		4.00%
Pension Benefits | Private equity	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	0.00%		'
Maximum Target Allocation	4.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	1.00%	[1]	1.00%
Postretirement Benefits	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%		100.00%
Postretirement Benefits | Cash And Cash Equivalents	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	0.00%		'
Maximum Target Allocation	10.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	4.00%		4.00%
Postretirement Benefits | Equity Securities	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	55.00%		'
Maximum Target Allocation	65.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	63.00%		62.00%
Postretirement Benefits | U.S. large capitalization	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	33.00%		'
Maximum Target Allocation	43.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	41.00%		40.00%
Postretirement Benefits | U.S. small and mid-capitalization	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	3.00%		'
Maximum Target Allocation	13.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	8.00%		8.00%
Postretirement Benefits | International	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	10.00%		'
Maximum Target Allocation	20.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	14.00%		14.00%
Postretirement Benefits | Debt Securities	'		'
Defined Benefit Plan Disclosure [Line Items]	'		'
Minimum Target Allocation	30.00%		'
Maximum Target Allocation	40.00%		'
Defined Benefit Plan, Actual Plan Asset Allocations	33.00%		34.00%
[1]	(a)Less than 1% of plan assets.

Retirement_Benefits_Fair_Value

Retirement Benefits (Fair Value Of Plan Assets Utilizing Fair Value Hierarchy) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Real estate	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Defined Benefit Plan, Purchases, Sales, and Settlements	$4		$3		'
Fair value of plan assets	131		118		108
Private equity	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Defined Benefit Plan, Purchases, Sales, and Settlements	-6		-5		'
Fair value of plan assets	15		19		23
Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	3,461	[1]	3,127	[1]	2,814	[1]
Pension Benefits | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	528		452		'
Pension Benefits | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	2,865		2,611		'
Pension Benefits | Significant Other Unobservable Inputs (Level 3)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	146		137		'
Pension Benefits | Cash And Cash Equivalents	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	44		29		'
Pension Benefits | Cash And Cash Equivalents | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	5		1		'
Pension Benefits | Cash And Cash Equivalents | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	39		28		'
Pension Benefits | U.S. large capitalization	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1,269		1,090		'
Pension Benefits | U.S. large capitalization | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	107		83		'
Pension Benefits | U.S. large capitalization | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1,162		1,007		'
Pension Benefits | U.S. small and mid-capitalization	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	273		235		'
Pension Benefits | U.S. small and mid-capitalization | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	273		235		'
Pension Benefits | U.S. small and mid-capitalization | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	0		0		'
Pension Benefits | International and emerging markets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	515		435		'
Pension Benefits | International and emerging markets | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	143		134		'
Pension Benefits | International and emerging markets | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	372		301		'
Pension Benefits | Corporate Bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	860		832		'
Pension Benefits | Corporate Bonds | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	860		832		'
Pension Benefits | Municipal Bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	149		176		'
Pension Benefits | Municipal Bonds | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	149		176		'
Pension Benefits | U.S. treasury and agency securities	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	256		250		'
Pension Benefits | U.S. treasury and agency securities | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	256		250		'
Pension Benefits | Asset-Backed Securities | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	10		'		'
Pension Benefits | Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	27		17		'
Pension Benefits | Other | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	27		17		'
Pension Benefits | Real estate	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	131		118		'
Pension Benefits | Real estate | Significant Other Unobservable Inputs (Level 3)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	131		118		'
Pension Benefits | Private equity	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	15		19		'
Pension Benefits | Private equity | Significant Other Unobservable Inputs (Level 3)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	15		19		'
Pension Benefits | Derivative assets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1		0		'
Pension Benefits | Derivative assets | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1		0		'
Pension Benefits | Derivative liabilities	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	-1		-1		'
Pension Benefits | Derivative liabilities | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	-1		-1		'
Pension Benefits | Medical benefit assets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	-112	[2]	-102	[2]	'
Pension Benefits | Net receivables	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	34	[3]	29	[3]	'
Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1,074	[1]	938	[1]	836	[1]
Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	490		439		'
Postretirement Benefits | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	511		443		'
Postretirement Benefits | Cash And Cash Equivalents	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	77		83		'
Postretirement Benefits | Cash And Cash Equivalents | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	77		83		'
Postretirement Benefits | Cash And Cash Equivalents | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	0		0		'
Postretirement Benefits | U.S. large capitalization	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	398		333		'
Postretirement Benefits | U.S. large capitalization | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	297		245		'
Postretirement Benefits | U.S. large capitalization | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	101		88		'
Postretirement Benefits | U.S. small and mid-capitalization	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	77		66		'
Postretirement Benefits | U.S. small and mid-capitalization | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	77		66		'
Postretirement Benefits | International	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	135		114		'
Postretirement Benefits | International | Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	39		45		'
Postretirement Benefits | International | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	96		69		'
Postretirement Benefits | Corporate Bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	89		88		'
Postretirement Benefits | Corporate Bonds | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	89		88		'
Postretirement Benefits | Municipal Bonds	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	103		91		'
Postretirement Benefits | Municipal Bonds | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	103		91		'
Postretirement Benefits | U.S. treasury and agency securities	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	72		67		'
Postretirement Benefits | U.S. treasury and agency securities | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	72		67		'
Postretirement Benefits | Asset-Backed Securities	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	10		18		'
Postretirement Benefits | Asset-Backed Securities | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	'		18		'
Postretirement Benefits | Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	40		22		'
Postretirement Benefits | Other | Significant Other Observable Inputs (Level 2)	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	40		22		'
Postretirement Benefits | Medical benefit assets	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	112	[2]	102	[2]	'
Postretirement Benefits | Net payables	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	-39	[4]	-46	[4]	'
Includes Medical Benefit Component Under Section401 H And Excludes Payables Related To Pending Security Sales [Member] | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1,074		938		'
Excludes Medical Benefit Component Under Section401 H And Includes Receivables Related To Pending Security Sales [Member] | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	3,461		3,127		'
Excludes Medical Benefit Component Under Section401 H And Excludes Payables Related To Pending Security Sales [Member] | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	1,001		882		'
Includes Medical Benefit Component Under Section401 H And Excludes Receivables Related To Pending Security Sales [Member] | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Fair value of plan assets	$3,539		$3,200		'
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
[2]	Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
[3]	Receivables related to pending security sales, offset by payables related to pending security purchases.
[4]	Payables related to pending security purchases, offset by Medicare, interest receivables, and receivables related to pending security sales.

Retirement_Benefits_Changes_In

Retirement Benefits (Changes In The Fair Value Of Plan Assets Classified As Level 3) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Real estate	'	'
Change in plan assets:	'	'
Fair value of plan assets at beginning of year	$118	$108
Actual Return on Plan Assets Related to Assets Still Held at the Reporting Date	9	7
Purchases, Sales and Settlements, net	4	3
Fair value of plan assets at end of year	131	118
Private equity	'	'
Change in plan assets:	'	'
Fair value of plan assets at beginning of year	19	23
Actual Return on Plan Assets Related to Assets Still Held at the Reporting Date	-9	-7
Actual Return on Plan Assets Related to Assets Sold During the Period	11	8
Purchases, Sales and Settlements, net	-6	-5
Fair value of plan assets at end of year	$15	$19

Retirement_Benefits_Components

Retirement Benefits (Components Of Net Periodic Benefit Cost) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Curtailment loss	($19)	[1],[2]	'		'
Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Service cost	91	[1],[3]	81	[1],[3]	73	[1]
Interest cost	163	[1],[3]	166	[1],[3]	175	[1]
Expected return on plan assets	-218	[1]	-208	[1]	-211	[1]
Transition obligation	'	[1]	'	[1]	'	[1]
Prior service cost	-2	[1]	-3	[1]	-1	[1]
Actuarial loss	87	[1]	75	[1]	41	[1]
Curtailment loss	-12	[1]	'		'
Net periodic benefit cost(b)	109	[1],[2]	111	[1],[4]	77	[1],[4]
Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Service cost	22	[1],[3]	22	[1],[3]	20	[1]
Interest cost	46	[1],[3]	47	[1],[3]	54	[1]
Expected return on plan assets	-62	[1]	-56	[1]	-50	[1]
Transition obligation	'	[1]	2	[1]	2	[1]
Prior service cost	-6	[1]	-6	[1]	-6	[1]
Actuarial loss	8	[1]	5	[1]	3	[1]
Curtailment loss	-7	[1]	'		'
Net periodic benefit cost(b)	1	[1],[2]	14	[1],[4]	23	[1],[4]
New Ameren Energy Resources Company, LLC | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost(b)	6	[1],[2]	9	[1],[2]	7	[1],[2]
New Ameren Energy Resources Company, LLC | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost(b)	$7	[1],[2]	'	[1],[2]	'	[1],[2]
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries
[2]	(b)The net periodic benefit cost includes a $6 million and a $7 million net gain for pension benefits and postretirement benefits, respectively, which was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). This net gain includes the curtailment gain recognized in 2013 as a result of a significant reduction in employees as of the December 2, 2013 closing date of the New AER divestiture. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.
[3]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
[4]	(c)The net periodic benefit cost includes $9 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2012 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). The net periodic benefit cost includes $7 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2011 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.

Retirement_Benefits_Summary_Of1

Retirement Benefits (Summary Of Estimated Amortizable Amounts From Regulatory Assets and Accumulated OCI Into Net Periodic Benefit Cost) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Pension Benefits	'
Defined Benefit Plan Disclosure [Line Items]	'
Prior service cost (credit)	($1)	[1]
Net actuarial loss	60	[1]
Net actuarial (gain) loss	1	[1]
Net periodic benefit cost	60	[1]
Postretirement Benefits	'
Defined Benefit Plan Disclosure [Line Items]	'
Prior service cost (credit)	-4	[1]
Net actuarial loss	9	[1]
Net actuarial (gain) loss	-2	[1]
Net periodic benefit cost	$3	[1]
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Retirement_Benefits_Summary_Of2

Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	$109	[1],[2]	$111	[1],[3]	$77	[1],[3]
Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	1	[1],[2]	14	[1],[3]	23	[1],[3]
Union Electric Company | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	69		63		51
Union Electric Company | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	8		10		11
Ameren Illinois Company | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	41		37		16
Ameren Illinois Company | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	'		4		11
Other | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	5		2		3
Other | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	'		'		1
Continuing Operations [Member] | Pension Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	115	[4]	102	[4]	70	[4]
Continuing Operations [Member] | Postretirement Benefits	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Net periodic benefit cost	$8	[4]	$14	[4]	$23	[4]
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries
[2]	(b)The net periodic benefit cost includes a $6 million and a $7 million net gain for pension benefits and postretirement benefits, respectively, which was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). This net gain includes the curtailment gain recognized in 2013 as a result of a significant reduction in employees as of the December 2, 2013 closing date of the New AER divestiture. See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.
[3]	(c)The net periodic benefit cost includes $9 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2012 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). The net periodic benefit cost includes $7 million and $- million in total net costs for pension benefits and postretirement benefits, respectively, for 2011 which were included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information on the divestiture.
[4]	(a)Includes amounts for Ameren registrant and nonregistrant subsidiaries

Retirement_Benefits_Schedule_O

Retirement Benefits (Schedule Of Expected Payments From Qualified Trust And Company Funds) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Pension Benefits | Paid From Qualified Trust	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	$247
2015	249
2016	255
2017	260
2018	264
2019 - 2023	1,342
Pension Benefits | Paid From Company Funds	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	3
2015	3
2016	3
2017	3
2018	3
2019 - 2023	14
Postretirement Benefits	'
Defined Benefit Plan Disclosure [Line Items]	'
2014, Federal Subsidy	3
2015, Federal Subsidy	4
2016, Federal Subsidy	4
2017, Federal Subsidy	4
2018, Federal Subsidy	4
2019 - 2023, Federal Subsidy	19
Postretirement Benefits | Paid From Qualified Trust	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	61
2015	63
2016	66
2017	69
2018	72
2019 - 2023	394
Postretirement Benefits | Paid From Company Funds	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	2
2015	2
2016	2
2017	2
2018	2
2019 - 2023	$12

Retirement_Benefits_Assumption1

Retirement Benefits (Assumptions Used To Determine Net Periodic Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Discount rate at measurement date	4.00%	4.50%	5.25%
Expected return on plan assets	7.50%	7.75%	8.00%
Increase in future compensation	3.50%	3.50%	3.50%
Medical cost trend rate (initial)	'	'	0.00%
Medical cost trend rate (ultimate)	'	'	0.00%
Postretirement Benefits	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Discount rate at measurement date	4.00%	4.50%	5.25%
Expected return on plan assets	7.25%	7.50%	7.75%
Increase in future compensation	3.50%	3.50%	3.50%
Medical cost trend rate (initial)	5.00%	5.50%	6.00%
Medical cost trend rate (ultimate)	5.00%	5.00%	5.00%
Years to ultimate rate	'	'1 year	'2 years

Retirement_Benefits_Schedule_O1

Retirement Benefits (Schedule Of Potential Changes In Key Assumptions) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Pension Benefits	'
Defined Benefit Plan Disclosure [Line Items]	'
Service Cost and Interest Cost, .25% decrease in discount rate	($2)
Benefit Obligation, .25% decrease in discount rate	109
Service Cost and Interest Cost, .25% increase in salary rate	2
Benefit Obligation, .25% increase in salary rate	17
Postretirement Benefits	'
Defined Benefit Plan Disclosure [Line Items]	'
Benefit Obligation, .25% decrease in discount rate	32
Service Cost and Interest Cost, 1.00% increase in annual medical trend	2
Benefit Obligation, 1.00% increase in annual medical trend	40
Service Cost and Interest Cost, 1.00% decrease in annual medical trend	-2
Benefit Obligation, 1.00% decrease in annual medical trend	($37)

Retirement_Benefits_Schedule_O2

Retirement Benefits (Schedule Of Matching Contributions) (Details) (401 (K), USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Employer contributions	$27	[1]	$26	[1]	$25	[1]
Union Electric Company	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Employer contributions	16		16		16
Ameren Illinois Company	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Employer contributions	10		9		8
Other	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Employer contributions	$1		$1		$1
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

StockBased_Compensation_Narrat

Stock-Based Compensation (Narrative) (Details) (USD $)	12 Months Ended			1 Months Ended		12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2013	Jan. 31, 2012	Dec. 31, 2013
				Performance Share Units	Performance Share Units	Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'
Maximum shares available for grants	4,000,000	'	'	'	'	'
Share-based compensation expense	$20	$22	$13	'	'	'
Employee service share-based compensation, tax benefit from compensation expense	8	8	5	'	'	'
Amounts paid to settle share units	11	11	4	'	'	'
Compensation cost not yet recognized	$20	'	'	'	'	'
Expected weighted average recognition period for share-based compensation expense, in months	'20 months	'	'	'	'	'
Performance period	'	'	'	'	'	'3 years
Percentage of shares issued per share unit, minimum	'	'	'	'	'	0.00%
Percentage of shares issued per share unit, maximum	'	'	'	'	'	200.00%
Fair value of each share unit, per share	'	'	'	$31.19	$35.68	$31.19	[1]
Closing common share price	'	'	'	$30.72	$33.13	'
Three-year risk-free rate	'	'	'	0.36%	0.41%	'
Volatility rate, minimum	'	'	'	12.00%	17.00%	'
Volatility rate, maximum	'	'	'	21.00%	31.00%	'
[1]	Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2013 under the 2006 Plan.

StockBased_Compensation_Summar

Stock-Based Compensation (Summary Of Nonvested Shares) (Details) (Performance Share Units, USD $)	1 Months Ended		12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Dec. 31, 2013
Performance Share Units	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]	'	'	'
Share Units, Nonvested at beginning of year	1,192,487	'	1,192,487
Share Units, Granted	'	'	840,482	[1]
Share Units, Unearned or forfeited	'	'	-29,730	[2]
Share Units, Earned and vested	'	'	-784,695	[3]
Share Units, Nonvested at end of year	'	'	1,218,544
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]	'	'	'
Weighted-average Fair Value per Unit, Nonvested at beginning of year	$33.56	'	$33.56
Weighted-averageFair Value per Unit, granted	$31.19	$35.68	$31.19	[1]
Weighted-average Fair Value per Unit, Unearned or forfeited	'	'	$31.93	[2]
Weighted-average Fair Value per Unit, Earned and vested	'	'	$31.60	[3]
Weighted-average Fair Value per Unit, Nonvested at end of year	'	'	$33.23
[1]	Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in 2013 under the 2006 Plan.
[2]	Includes share units granted in 2011 that were not earned based on performance provisions of the award grants.
[3]	Includes share units granted in 2011 that vested as of December 31, 2013, that were earned pursuant to the provisions of the award grants. Also includes share units that vested due to attainment of retirement eligibility by certain employees and certain employees whose employment terminated on December 2, 2013, with the divestiture of New AER. Actual shares issued for retirement-eligible employees and former New AER subsidiaries' employees will vary depending on actual performance over the three-year measurement period.

Income_Taxes_Schedule_Of_Effec

Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Taxes [Line Items]	'		'		'
Statutory federal income tax rate:	35.00%		35.00%		35.00%
Depreciation differences	'		-1.00%		-1.00%
Amortization of investment tax credit	-1.00%		-1.00%		-1.00%
State tax	4.00%		5.00%		4.00%
Other permanent items(a)	'		'		1.00%
Other permanent items	'		-1.00%	[1]	'
Tax credits	'		'		-1.00%
Effective income tax rate	38.00%		37.00%		37.00%
Union Electric Company	'		'		'
Income Taxes [Line Items]	'		'		'
Statutory federal income tax rate:	35.00%		35.00%		35.00%
Depreciation differences	0.00%		-1.00%		-2.00%
Amortization of investment tax credit	-1.00%		-1.00%		-1.00%
State tax	3.00%		3.00%		3.00%
Other permanent items(a)	'		1.00%		'
Other permanent items	1.00%	[1]	0.00%		1.00%	[1]
Tax credits	'		'		'
Effective income tax rate	38.00%		37.00%		36.00%
Ameren Illinois Company	'		'		'
Income Taxes [Line Items]	'		'		'
Statutory federal income tax rate:	35.00%		35.00%		35.00%
Depreciation differences	-1.00%		'		'
Amortization of investment tax credit	0.00%		-1.00%		-1.00%
State tax	6.00%		6.00%		5.00%
Other permanent items(a)	'		'		'
Other permanent items	'		'		'
Tax credits	'		'		'
Effective income tax rate	40.00%		40.00%		39.00%
[1]	Permanent items are treated differently for book and tax purposes and primarily include non-taxable income related to company-owned life insurance and deductions related to dividends on DRPlus and the 401(k) plan for Ameren, as well as nondeductible expenses related to lobbying and stock issuance costs for Ameren Missouri.

Income_Taxes_Schedule_Of_Compo

Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Taxes [Line Items]	'		'		'
Current Federal taxes	($118)	[1]	$40	[1]	($6)	[1]
Current State taxes	19	[1]	10	[1]	-2	[1]
Deferred Federal taxes	368	[1]	204	[1]	213	[1]
Deferred State taxes	48	[1]	60	[1]	55	[1]
Deferred investment tax credits, amortization	-6	[1]	-7	[1]	-6	[1]
Total income tax expense	311	[1]	307	[1]	254	[1]
Union Electric Company	'		'		'
Income Taxes [Line Items]	'		'		'
Current Federal taxes	136		-25		3
Current State taxes	41		-10		2
Deferred Federal taxes	64		248		129
Deferred State taxes	6		44		31
Deferred investment tax credits, amortization	-5		-5		-4
Total income tax expense	242		252		161
Ameren Illinois Company	'		'		'
Income Taxes [Line Items]	'		'		'
Current Federal taxes	-15		-7		-24
Current State taxes	21		-3		-4
Deferred Federal taxes	99		76		123
Deferred State taxes	6		30		34
Deferred investment tax credits, amortization	-1		-2		-2
Total income tax expense	110		94		127
Other Affiliates [Member]	'		'		'
Income Taxes [Line Items]	'		'		'
Current Federal taxes	-239	[2]	72		15
Current State taxes	-43	[2]	23		0
Deferred Federal taxes	205	[2]	-120		-39
Deferred State taxes	36	[2]	-14		-10
Deferred investment tax credits, amortization	0		0		0
Total income tax expense	($41)		($39)		($34)
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
[2]	These amounts are substantially related to the reversal of unrecognized tax benefits as a result of new IRS guidance related to the deductibility of expenditures to maintain, replace or improve steam or electric power generation property, along with casualty loss deductions for storm damage. They also reflect the increase in deferred tax expense due to available net operating losses.

Income_Taxes_Schedule_Of_Defer

Income Taxes (Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Income Taxes [Line Items]	'		'
Plant related	$3,769	[1]	$3,550	[1]
Regulatory assets (liabilities), net	76	[1]	73	[1]
Deferred benefit costs	-273	[1]	-323	[1]
Purchase accounting	-28	[1]	-28	[1]
ARO	-6	[1]	-6	[1]
Other	-478	[1],[2],[3]	-250	[1],[2]
Total net accumulated deferred income tax liabilities	3,060	[1],[4]	3,016	[1],[5]
Deferred Tax Assets, Valuation Allowance	7		'
Current assets	106		170
Union Electric Company	'		'
Income Taxes [Line Items]	'		'
Plant related	2,513		2,385
Regulatory assets (liabilities), net	74		73
Deferred benefit costs	-74		-84
Purchase accounting	'		'
ARO	-7		-7
Other	-17	[2]	50	[2]
Total net accumulated deferred income tax liabilities	2,489	[4]	2,417	[5]
Deferred Tax Assets, Valuation Allowance	1		'
Current assets	20		26
Ameren Illinois Company	'		'
Income Taxes [Line Items]	'		'
Plant related	1,243		1,145
Regulatory assets (liabilities), net	2		'
Deferred benefit costs	-85		-102
Purchase accounting	-27		-27
ARO	1		1
Other	-63	[2]	-77	[2]
Total net accumulated deferred income tax liabilities	1,071	[4]	940	[5]
Deferred Tax Assets, Valuation Allowance	1		'
Current assets	45		85
Other Affiliates [Member]	'		'
Income Taxes [Line Items]	'		'
Plant related	13		20
Regulatory assets (liabilities), net	'		'
Deferred benefit costs	-114		-137
Purchase accounting	-1		-1
ARO	0		0
Other	-398	[2]	-223	[2]
Total net accumulated deferred income tax liabilities	($500)	[4]	($341)	[5]
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
[2]	Includes deferred tax assets related to net operating loss and tax credit carryforwards detailed in the table below.
[3]	Includes total valuation allowances for Ameren, Ameren Missouri, and Ameren Illinois of $7 million, $1 million, and $1 million, respectively, as of December 31, 2013. The state valuation allowances are shown in the table below.
[4]	Includes $20 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2013.
[5]	Includes $26 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2012.

Income_Taxes_Schedule_Of_Net_O

Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	$408	[1]	$200	[1]
Tax credit carryforwards	118	[1]	109	[1]
Change in valuation allowance	2		1
Federal	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	360	[1],[2]	173	[1],[3]
Tax credit carryforwards	88	[1],[4]	86	[1],[4]
Net operating loss carryforward, expiration period start	1-Jan-28		1-Jan-28
Tax credit carryforward, expiration period start	1-Jan-29		1-Jan-29
State	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	48	[1],[5]	27	[1],[6]
Tax credit carryforwards	34	[1],[7]	25	[1],[8]
Tax Credit Carryforward, Valuation Allowance	4	[1],[9]	2	[1],[10]
Net operating loss carryforward, expiration period start	1-Jan-17		1-Jan-17
Tax credit carryforward, expiration period start	1-Jan-14		1-Jan-13
Union Electric Company	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	64		64
Tax credit carryforwards	12		11
Union Electric Company | Federal	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	61	[2]	61	[3]
Tax credit carryforwards	12	[4]	11	[4]
Union Electric Company | State	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	3	[5]	3	[6]
Tax credit carryforwards	1	[7]	1	[8]
Tax Credit Carryforward, Valuation Allowance	-1	[9]	-1	[10]
Ameren Illinois Company	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	95		72
Tax credit carryforwards	'		'
Change in valuation allowance	'		1
Ameren Illinois Company | Federal	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	84	[2]	61	[3]
Tax credit carryforwards	'		0	[4]
Ameren Illinois Company | State	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	11	[5]	11	[6]
Tax credit carryforwards	1	[7]	1	[8]
Tax Credit Carryforward, Valuation Allowance	-1	[9]	-1	[10]
Other Affiliates [Member]	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	249		64
Tax credit carryforwards	106		98
Other Affiliates [Member] | Federal	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	215	[2]	51	[3]
Tax credit carryforwards	76	[4]	75	[4]
Other Affiliates [Member] | State	'		'
Operating Loss Carryforwards [Line Items]	'		'
Net operating loss carryforwards	34	[5]	13	[6]
Tax credit carryforwards	32	[7]	23	[8]
Tax Credit Carryforward, Valuation Allowance	($2)	[9]	$0	[10]
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
[2]	These will begin to expire in 2028.
[3]	These will begin to expire in
[4]	These will begin to expire in 2029.
[5]	These will begin to expire in 2017.
[6]	These will begin to expire in2017.
[7]	These will begin to expire in 2014.
[8]	These began to expire in 2013.
[9]	This balance increased by $2 million, $- million and $- million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2013.
[10]	This balance increased by $1 million, $- million and $1 million for Ameren, Ameren Missouri and Ameren Illinois, respectively, during 2012.

Income_Taxes_Schedule_Of_Chang

Income Taxes (Schedule Of Changes To Unrecognized Tax Benefits And Related Interest) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Mar. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'		'		'		'
Unrecognized tax benefits	$156	[1]	$148	[1]	$246	[1]	$48
Increases based on tax positions	7	[1]	5	[1]	22	[1]	'
Decreases based on tax positions	-143	[1]	-13	[1]	-125	[1]	'
Increases based on tax positions related to current period	69	[1]	17	[1]	17	[1]	'
Changes related to settlements with taxing authorities	'	[1]	0		-10	[1]	'
Decreases related to the lapse of statute of limitations	1	[1]	-1	[1]	-2	[1]	'
Unrecognized tax benefits	90	[1]	156	[1]	148	[1]	48
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	54	[1]	1	[1]	1	[1]	'
Union Electric Company	'		'		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'		'		'		'
Unrecognized tax benefits	136		124		164		15
Increases based on tax positions	0		4		15		'
Decreases based on tax positions	-122		-7		-63		'
Increases based on tax positions related to current period	16		15		13		'
Changes related to settlements with taxing authorities	'		0		-5		'
Decreases related to the lapse of statute of limitations	1		'		'		'
Unrecognized tax benefits	31		136		124		15
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	3		3		1		'
Ameren Illinois Company	'		'		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'		'		'		'
Unrecognized tax benefits	13		11		56		'
Increases based on tax positions	2		'		0		'
Decreases based on tax positions	-16		-1		-41		'
Increases based on tax positions related to current period	0		3		0		'
Changes related to settlements with taxing authorities	'		0		-4		'
Decreases related to the lapse of statute of limitations	'		'		'		'
Unrecognized tax benefits	-1		13		11		'
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	0		-1		'		'
Other Affiliates [Member]	'		'		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'		'		'		'
Unrecognized tax benefits	7		13		26		'
Increases based on tax positions	5		1		7		'
Decreases based on tax positions	-5		-5		-21		'
Increases based on tax positions related to current period	53	[2]	-1		4		'
Changes related to settlements with taxing authorities	'		0		-1		'
Decreases related to the lapse of statute of limitations	'		-1		-2		'
Unrecognized tax benefits	60		7		13		'
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	$51	[2]	($1)		'		'
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries.
[2]	Primarily due to tax positions relating to the New AER divestiture. The income statement impact of this unrecognized tax benefit was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information.

Income_Taxes_Reconciliation_Of

Income Taxes (Reconciliation Of The Change In The Liability For Interest On Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Income Tax Contingency [Line Items]	'		'		'
Liability for interest	$6	[1]	$5	[1]	$17	[1]
Interest charges (income)	-5	[1]	1	[1]	-11	[1]
Interest payment	'		'		-1	[1]
Liability for interest	1	[1]	6	[1]	5	[1]
Union Electric Company	'		'		'
Income Tax Contingency [Line Items]	'		'		'
Liability for interest	8		6		10
Interest charges (income)	-8		2		-3
Interest payment	'		'		-1
Liability for interest	0		8		6
Ameren Illinois Company	'		'		'
Income Tax Contingency [Line Items]	'		'		'
Liability for interest	1		1		2
Interest charges (income)	-1		0		-1
Interest payment	'		'		0
Liability for interest	0		1		1
Other Affiliates [Member]	'		'		'
Income Tax Contingency [Line Items]	'		'		'
Liability for interest	-3		-2		5
Interest charges (income)	4		-1		-7
Interest payment	'		'		0
Liability for interest	$1		($3)		($2)
[1]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2012

Dec. 31, 2011

Jan. 31, 2011

Jan. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2011

Dec. 31, 2011

Dec. 31, 2015

Dec. 31, 2025

Illinois Corporate Income Tax

Minimum

Maximum

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Income Tax Rate in 2015

Income Tax Rate in 2025

Illinois Corporate Income Tax

Illinois Corporate Income Tax

Illinois Corporate Income Tax

Illinois Corporate Income Tax

Illinois Corporate Income Tax

Income Taxes [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

State corporate income tax rate

4.00%

5.00%

4.00%

'

'

7.30%

9.50%

3.00%

3.00%

3.00%

'

6.00%

6.00%

5.00%

'

'

7.75%

7.30%

Increase in current state and local tax expense benefit

'

'

'

'

$6

'

'

'

'

'

'

'

'

'

'

$4

'

'

Decrease in deferred state and local income tax expense benefit

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

3

'

'

Reduction of uncertain tax positions

'

'

'

39

'

'

'

'

'

'

17

'

'

'

12

'

'

'

Estimated Unrecognized Tax Benefits, Decreases Resulting From Settlements with Taxing Authorities

20

'

'

'

'

'

'

13

'

'

'

'

'

'

'

'

'

'

Unrecognized Tax Benefits, Decrease Resulting from Current Period Tax Positions

$103

'

'

'

'

'

'

$95

'

'

'

$5

'

'

'

'

'

'

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Union Electric Company	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	$25		$20		$23
Operating Expenses	116		106		114
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	3		1	[1]	2
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	21		19		16
Union Electric Company | Ameren Missouri and Ameren Illinois miscellaneous support services	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	1		1		5
Union Electric Company | Ameren Illinois Power Supply Agreements with Ameren Missouri	'		'		'
Related Party Transaction [Line Items]	'		'		'
Interest (Charges) Income	'		'		'
Union Electric Company | Ameren Services Support Services Agreement	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Expenses	116		106		114
Union Electric Company | Insurance Premiums	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Expenses	1	[1],[2]	1	[1],[2]	1	[1],[2]
Union Electric Company | Money Pool	'		'		'
Related Party Transaction [Line Items]	'		'		'
Interest (Charges) Income	1	[1]	1	[1]	'
Ameren Illinois Company	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	4		1		3
Operating Expenses	93		88		87
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	1		1		2
Ameren Illinois Company | Ameren Missouri and Ameren Illinois miscellaneous support services	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Revenues	3		1	[1]	1
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Expenses	3		1	[1]	2
Interest (Charges) Income	'		'		'
Ameren Illinois Company | Ameren Illinois transmission agreements with ATXI	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Expenses	2		3		3
Ameren Illinois Company | Purchased Power	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Expenses	5		3		5
Ameren Illinois Company | Ameren Services Support Services Agreement	'		'		'
Related Party Transaction [Line Items]	'		'		'
Operating Expenses	93		88		87
Ameren Illinois Company | Money Pool	'		'		'
Related Party Transaction [Line Items]	'		'		'
Interest (Charges) Income	$1	[1]	$1	[1]	'
[1]	Amount less than $1 million.
[2]	Represents insurance premiums paid to Energy Risk Assurance Company, an affiliate for replacement power, property damage, and terrorism coverage.

Related_Party_Transactions_Nar

Related Party Transactions (Narrative) (Details) (USD $)	1 Months Ended
In Millions, unless otherwise specified	Apr. 30, 2011	Jan. 31, 2011	Apr. 30, 2012	31-May-11	Apr. 30, 2012	31-May-11	Apr. 30, 2010	31-May-11
	Ameren Illinois Company	Ameren Illinois Company	Period Five	Period Five	Period Six	Period Three	Period Four	Period Four
	Ameren Transmission Company of Illinois	Ameren Transmission Company of Illinois	Union Electric Company	Ameren Illinois Company	Union Electric Company	Ameren Illinois Company	Union Electric Company	Ameren Illinois Company
				Union Electric Company		Union Electric Company		Union Electric Company
				MWh		MWh		MWh
Related Party Transaction [Line Items]	'	'	'	'	'	'	'	'
Energy Supply Agreements Amount	'	'	$1	'	$3	'	$1	'
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power	'	'	'	40,800	'	16,800	'	40,800
Long-term Contract for Purchase of Electric Power, Related Party Contract, Fixed Power, Rate	'	'	'	28	'	37	'	29
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress, Proceeds from Advances to Related Party	'	52	'	'	'	'	'	'
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress, Proceeds from Advances to Related Party, Accrued Interest	'	3	'	'	'	'	'	'
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress, Transfers from Related Party	$20	'	'	'	'	'	'	'

Commitments_And_Contingencies_1

Commitments And Contingencies (Callaway Nuclear Energy Center) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	$13,616,000,000	[1]
Insurance maximum coverage per incident	128,000,000
Threshold for which a retrospective assessment for a covered loss is necessary	375,000,000
Annual payment in the event of an incident at any licensed commercial reactor	19,000,000
Aggregate maximum assessment per incident under Price-Anderson liability provisions of Atomic Energy Act	128,000,000
Maximum annual payment to be paid in a calendar year per reactor incident under liability provisions of Atomic Energy Act	19,000,000
Amount of coverage in excess of primary property liability coverage	2,250,000,000
Sub-limit of Amount of Coverage in Excess of Primary Property Liability Coverage for Non-Nuclear Events	1,700,000,000
Amount of weekly indemnity coverage commencing eight weeks after power outage	4,500,000
Number of weeks of coverage after the first eight weeks of an outage	'P52W
Amount of additional weekly indemnity coverage commencing after initial indemnity coverage	3,600,000
Number of additional weeks after initial indemnity coverage for power outage, minimum	'P71W
Amount of weekly indemnity coverage thereafter not exceeding policy limit	490,000,000
Amount of secondary weekly indemnity coverage for prolonged nuclear plant outage in excess of primary indemnity coverage	900,000
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period	3,240,000,000
Public Liability And Nuclear Worker Liability - American Nuclear Insurers	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	375,000,000
Insurance maximum coverage per incident	0
Public Liability And Nuclear Worker Liability - Pool Participation	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	13,241,000,000	[2]
Insurance maximum coverage per incident	128,000,000	[3]
Property Damage - Nuclear Electric Insurance Ltd	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	2,250,000,000	[4]
Insurance maximum coverage per incident	23,000,000	[5]
Sub-limit of Amount of Coverage in Excess of Primary Property Liability Coverage for Non-Nuclear Events	200,000,000
Replacement Power - Nuclear Electric Insurance Ltd	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	490,000,000	[6]
Insurance maximum coverage per incident	9,000,000	[5]
Sub-limit of Amount of Weekly indemnity Coverage Thereafter Not Exceeding Policy Limit for Non-Nuclear Events	327,600,000
Replacement Power - Energy Risk Assurance Company	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	64,000,000	[7]
Insurance maximum coverage per incident	0
Property Damage European Mutual Association for Nuclear Insurance	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	500,000,000	[8]
Amount of primary property liability coverage	500,000,000
Property Damage	'
Commitments and Contingencies [Line Items]	'
Insurance aggregate maximum coverage	2,750,000,000
Insurance maximum coverage per incident	$23,000,000
[1]	Limit of liability for each incident under the Price-Anderson Act liability provisions of the Atomic Energy Act of 1954, as amended. A company could be assessed up to $128 million per incident for each licensed reactor it operates with a maximum of $19 million per incident to be paid in a calendar year for each reactor. This limit is subject to change to account for the effects of inflation and changes in the number of licensed reactors.
[2]	Provided through mandatory participation in an industrywide retrospective premium assessment program.
[3]	Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $375 million in the event of an incident at any licensed United States commercial reactor, payable at $19 million per year.
[4]	Nuclear Electric Insurance Limited provides $2.25 billion in property damage, decontamination, and premature decommissioning insurance. There is a $1.7 billion sublimit for non-radiation events, of which the top $200 million is a shared limit with other generators purchasing this coverage and includes one free reinstatement.
[5]	All Nuclear Electric Insurance Limited insured plants could be subject to assessments should losses exceed the accumulated funds from Nuclear Electric Insurance Limited.
[6]	Provides replacement power cost insurance in the event of a prolonged accidental outage at our nuclear energy center. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first eight weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Effective April 1, 2013, non-radiation events are sub-limited to $327.6 million.
[7]	Provides replacement power cost insurance in the event of a prolonged accidental outage at our nuclear energy center. The coverage commences after the first 52 weeks of insurance coverage from Nuclear Electric Insurance Limited and is a weekly indemnity of $900,000 for 71 weeks in excess of the $3.6 million per week set forth above. Missouri Energy Risk Assurance Company LLC is an affiliate and has reinsured this coverage with third-party insurance companies. See Note 14 – Related Party Transactions for more information on this affiliate transaction.
[8]	European Mutual Association for Nuclear Insurance provides $500 million in excess of the $2.25 billion property coverage and $1.7 billion non-radiation coverage.

Commitments_And_Contingencies_2

Commitments And Contingencies (Schedule Of Lease Obligations) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Commitments and Contingencies [Line Items]	'		'		'
Capital lease payments, 2014	$32	[1],[2]	'		'
Capital lease payments, 2015	33	[1],[2]	'		'
Capital lease payments, 2016	33	[1],[2]	'		'
Capital lease payments, 2017	33	[1],[2]	'		'
Capital lease payments, 2018	32	[1],[2]	'		'
Capital lease payments, After 5 Years	393	[1],[2]	'		'
Capital lease payments, Total	556	[1],[2]	'		'
Less Amount representing interest, 2014	27	[2]	'		'
Less Amount representing interest, 2015	27	[2]	'		'
Less Amount representing interest, 2016	27	[2]	'		'
Less Amount representing interest, 2017	27	[2]	'		'
Less Amount representing interest, 2018	26	[2]	'		'
Less Amount representing interest, After 5 Years	123	[2]	'		'
Less Amount representing interest, Total	257	[2]	'		'
Present value of minimum capital lease payments, 2014	5	[2]	'		'
Present value of minimum capital lease payments, 2015	6	[2]	'		'
Present value of minimum capital lease payments, 2016	6	[2]	'		'
Present value of minimum capital lease payments, 2017	6	[2]	'		'
Present value of minimum capital lease payments, 2018	6	[2]	'		'
Present value of minimum capital lease payments, After 5 Years	270	[2]	'		'
Present value of minimum capital lease payments, Total	299	[2]	'		'
Operating leases, 2014	14	[2],[3]	'		'
Operating leases, 2015	13	[2],[3]	'		'
Operating leases, 2016	13	[2],[3]	'		'
Operating leases, 2017	13	[2],[3]	'		'
Operating leases, 2018	13	[2],[3]	'		'
Operating leases, After 5 Years	51	[2],[3]	'		'
Operating leases, Total	117	[2],[3]	'		'
Total lease obligations, 2014	19	[2]	'		'
Total lease obligations, 2015	19	[2]	'		'
Total lease obligations, 2016	19	[2]	'		'
Total lease obligations, 2017	19	[2]	'		'
Total lease obligations, 2018	19	[2]	'		'
Total lease obligations, After 5 Years	321	[2]	'		'
Total lease obligations, Total	416	[2]	'		'
Annual obligation for real estate leases and railroad licenses	2		'		'
Total rental expense	32	[4]	33	[4]	36	[4]
Union Electric Company	'		'		'
Commitments and Contingencies [Line Items]	'		'		'
Capital lease payments, 2014	32	[1]	'		'
Capital lease payments, 2015	33	[1]	'		'
Capital lease payments, 2016	33	[1]	'		'
Capital lease payments, 2017	33	[1]	'		'
Capital lease payments, 2018	32	[1]	'		'
Capital lease payments, After 5 Years	393	[1]	'		'
Capital lease payments, Total	556	[1]	'		'
Less Amount representing interest, 2014	27		'		'
Less Amount representing interest, 2015	27		'		'
Less Amount representing interest, 2016	27		'		'
Less Amount representing interest, 2017	27		'		'
Less Amount representing interest, 2018	26		'		'
Less Amount representing interest, After 5 Years	123		'		'
Less Amount representing interest, Total	257		'		'
Present value of minimum capital lease payments, 2014	5		'		'
Present value of minimum capital lease payments, 2015	6		'		'
Present value of minimum capital lease payments, 2016	6		'		'
Present value of minimum capital lease payments, 2017	6		'		'
Present value of minimum capital lease payments, 2018	6		'		'
Present value of minimum capital lease payments, After 5 Years	270		'		'
Present value of minimum capital lease payments, Total	299		'		'
Operating leases, 2014	11	[3]	'		'
Operating leases, 2015	11	[3]	'		'
Operating leases, 2016	11	[3]	'		'
Operating leases, 2017	12	[3]	'		'
Operating leases, 2018	11	[3]	'		'
Operating leases, After 5 Years	50	[3]	'		'
Operating leases, Total	106	[3]	'		'
Total lease obligations, 2014	16		'		'
Total lease obligations, 2015	17		'		'
Total lease obligations, 2016	17		'		'
Total lease obligations, 2017	18		'		'
Total lease obligations, 2018	17		'		'
Total lease obligations, After 5 Years	320		'		'
Total lease obligations, Total	405		'		'
Annual obligation for real estate leases and railroad licenses	1		'		'
Total rental expense	29		29		29
Ameren Illinois Company	'		'		'
Commitments and Contingencies [Line Items]	'		'		'
Operating leases, 2014	2	[3]	'		'
Operating leases, 2015	1	[3]	'		'
Operating leases, 2016	1	[3]	'		'
Operating leases, 2017	1	[3]	'		'
Operating leases, 2018	1	[3]	'		'
Operating leases, After 5 Years	1	[3]	'		'
Operating leases, Total	7	[3]	'		'
Annual obligation for real estate leases and railroad licenses	1		'		'
Total rental expense	$21		$19		$17
[1]	See Properties under Part I, Item 2, and Note 3 – Property and Plant, Net, of this report for additional information.
[2]	ncludes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.
[3]	Amounts related to certain land-related leases have indefinite payment periods. The annual obligation of $2 million, $1 million and $1 million for Ameren, Ameren Missouri and Ameren Illinois for these items is included in the 2014 through 2018 columns, respectively.
[4]	Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

Commitments_And_Contingencies_3

Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2015

Dec. 31, 2014

In Millions, unless otherwise specified

Coal

Natural Gas

Nuclear Fuel

Purchased Power

Methane Gas

Other

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Union Electric Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Ameren Illinois Company

Investment in Energy Efficiency Programs

Investment in Energy Efficiency Programs

Coal

Natural Gas

Nuclear Fuel

Purchased Power

Methane Gas

Other

Coal

Natural Gas

Nuclear Fuel

Purchased Power

Methane Gas

Other

Union Electric Company

Union Electric Company

Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2014

$1,519

[1]

$620

[1]

$323

[1]

$64

[1]

$308

[1],[2]

$3

[1]

$201

[1]

$895

$620

$62

$64

$19

[2]

$3

$127

$573

'

$261

'

$289

[2]

'

$23

'

$48

2015

1,195

[1]

642

[1]

179

[1]

63

[1]

164

[1],[2]

4

[1]

143

[1]

861

642

32

63

19

[2]

4

101

316

'

147

'

145

[2]

'

24

64

'

2016

993

[1]

664

[1]

90

[1]

81

[1]

78

[1],[2]

4

[1]

76

[1]

827

664

19

81

19

[2]

4

40

154

'

71

'

59

[2]

'

24

'

'

2017

888

[1]

676

[1]

45

[1]

58

[1]

55

[1],[2]

4

[1]

50

[1]

794

676

11

58

19

[2]

4

26

94

'

34

'

36

[2]

'

24

'

'

2018

313

[1]

120

[1]

28

[1]

57

[1]

52

[1],[2]

5

[1]

51

[1]

236

120

8

57

19

[2]

5

27

77

'

20

'

33

[2]

'

24

'

'

Thereafter

1,441

[1]

125

[1]

82

[1]

158

[1]

635

[1],[2]

91

[1]

350

[1]

695

125

28

158

110

[2]

91

183

746

'

54

'

525

[2]

'

167

'

'

Total

$6,349

[1]

$2,847

[1]

$747

[1]

$481

[1]

$1,292

[1],[2]

$111

[1]

$871

[1]

$4,308

$2,847

$160

$481

$205

[2]

$111

$504

$1,960

'

$587

'

$1,087

[2]

'

$286

'

'

Renewable Energy Credits Agreements, Term

'

'

'

'

'20 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

[2]

The purchased power amounts for Ameren and Ameren Illinois include 20-year agreements for renewable energy credits that were entered into in December 2010 with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.

Commitments_And_Contingencies_4

Commitments And Contingencies (Environmental Matters) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Manufactured Gas Plant	'
Loss contingency range of possible loss, minimum	$278
Loss contingency range of possible loss, maximum	338
Accrual for environmental loss contingencies	278	[1]
Manufactured Gas Plant | Union Electric Company	'
Loss contingency range of possible loss, minimum	4
Loss contingency range of possible loss, maximum	5
Accrual for environmental loss contingencies	4	[1]
Manufactured Gas Plant | Ameren Illinois Company	'
Number of remediation sites	44
Loss contingency range of possible loss, minimum	274
Loss contingency range of possible loss, maximum	333
Accrual for environmental loss contingencies	274	[1]
Former Coal Ash Landfill | Ameren Illinois Company	'
Loss contingency range of possible loss, minimum	0.5
Loss contingency range of possible loss, maximum	6
Accrual for environmental loss contingencies	0.5
Other Environmental | Ameren Illinois Company	'
Accrual for environmental loss contingencies	0.8
Former Coal Tar Distillery | Union Electric Company	'
Loss contingency range of possible loss, minimum	2
Loss contingency range of possible loss, maximum	5
Accrual for environmental loss contingencies	2
Sauget Area 2 | Union Electric Company	'
Loss contingency range of possible loss, minimum	0.3
Loss contingency range of possible loss, maximum	10
Accrual for environmental loss contingencies	0.3
Substation in St Charles, Missouri | Union Electric Company	'
Loss contingency range of possible loss, minimum	1.6
Loss contingency range of possible loss, maximum	4.5
Accrual for environmental loss contingencies	1.6
Minimum	'
Estimated capital costs to comply with existing and known federal and state air emissions regulations	275
Maximum	'
Estimated capital costs to comply with existing and known federal and state air emissions regulations	$350
[1]	Recorded liability represents the estimated minimum probable obligations, as no other amount within the range provided a better estimate.

Commitments_And_Contingencies_5

Commitments And Contingencies (Pumped-Storage Hydroelectric Facility Breach) (Details) (Union Electric Company, USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Union Electric Company	'
Commitments and Contingencies [Line Items]	'
Insurance Settlements Receivable	$68

Commitments_And_Contingencies_6

Commitments And Contingencies (Asbestos-Related Litigation And Tax Exemptions And Credits) (Details) (USD $)	12 Months Ended							1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Jul. 31, 2013
	Asbestos-Related		Parent Company	Union Electric Company	Ameren Illinois Company	Ameren Illinois Company	Ameren Illinois Company	State	State
	defendant		Asbestos-Related	Asbestos-Related	Asbestos-Related	Collectibility of Taxes	Collectibility of Taxes	Ameren Illinois Company	Ameren Illinois Company
							customer	Collectibility of Taxes	Collectibility of Taxes
Loss Contingencies [Line Items]	'		'	'	'	'	'	'	'
Number of defendants	82		'	'	'	'	'	'	'
Number of pending asbestos lawsuits as of the balance sheet date	71,000,000	[1]	1,000,000	47,000,000	50,000,000	'	'	'	'
Percent of allowed cash expenditures in excess of base rates to be recovered through charges assessed to customers	90.00%		'	'	'	'	'	'	'
Asbestos trust fund balance	$23		'	'	'	'	'	'	'
Percent of difference to be contributed to the asbestos trust fund if cash expenditures are less than amount included in base electric rates.	90.00%		'	'	'	'	'	'	'
Number of customers affected	'		'	'	'	'	2,400	'	'
Loss Contingency, Damages Awarded, Value	'		'	'	'	'	'	0.5	4
Loss contingency range of possible loss, minimum	11		'	5	6	1	'	'	'
Loss contingency range of possible loss, maximum	'		'	'	'	5	'	'	'
Loss Contingency Accrual, at Carrying Value	'		'	'	'	$1	'	'	'
[1]	(a)Total does not equal the sum of the subsidiary unit lawsuits because some of the lawsuits name multiple Ameren entities as defendants.

Divestiture_Transactions_and_D2

Divestiture Transactions and Discontinued Operations (Narrative) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Mar. 14, 2013

Jan. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Jan. 31, 2014

In Millions, unless otherwise specified

Shutdown Of Meredosia And Hutsonville Energy Centers [Member]

Shutdown Of Meredosia And Hutsonville Energy Centers [Member]

Shutdown Of Meredosia And Hutsonville Energy Centers [Member]

New Ameren Energy Resources Company, LLC

New Ameren Energy Resources Company, LLC

New Ameren Energy Resources Company, LLC

Notes Payable, Other Payables

Elgin, Gibson City and Grand Tower Energy Centers

Merchant Generation

Merchant Generation

Merchant Generation

Ameren Energy Marketing Company

Guarantee Type, Other [Member]

Subsequent Event

New Ameren Energy Resources Company, LLC

Duck Creek Energy Center

Elgin, Gibson City and Grand Tower Energy Centers

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Asset retirement obligations

$369

$349

'

$31

$26

'

'

'

'

'

'

'

'

'

'

'

Disposal Group, Including Discontinued Operation, Working Capital Adjustment, Period

'

'

'

'

'

'

'120 days

'

'

'

'

'

'

'

'

'

Converted instrument, period for conversion

'

'

'

'

'

'

'

'

'24 months

'

'

'

'

'

'

'

Notes, Loans and Financing Receivable, Net, Noncurrent

'

'

'

'

'

'

'

'

18

'

'

'

'

'

'

'

Transaction agreement, cash retained by counterparty

'

'

'

'

'

235

'

'

'

'

'

'

'

'

'

'

Obligation to provide credit support, period

'

'

'

'

'

'24 months

'

'

'

'

'

'

'

'

'

'

Buyer's indemnification guarantee obligation

'

'

'

'

'

25

'

'

'

'

'

'

'

'

'

'

Buyer's indemnification guarantee obligation, period

'

'

'

'

'

'24 months

'

'

'

'

'

'

'

'

'

'

Impairment of assets to be disposed of

'

'

'

'

'

'

'

'

'

'

201

1,950

628

'

'

'

Disposal group, fair value

'

'

'

'

'

'

'

'

'

137.5

'

'

'

'

'

'

Discontinued operations deferred tax expense

'

'

'

'

'

'

'

'

'

'

99

'

'

'

'

'

Discontinued operations deferred tax benefit

'

'

'

'

'

'

'

'

'

'

86

'

'

'

'

'

Related Party Transaction, Guarantees Outstanding

190

'

'

'

'

'

'

'

'

'

'

'

'

176

14

'

Related Party Transaction, Guarantees, Maximum Exposure

'

'

'

'

'

'

'

'

'

'

'

'

'

6

'

'

Letters of Credit Outstanding, Amount

11

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss contingency range of possible loss, maximum

'

'

'

'

'

'

'

39

'

'

'

'

'

'

'

'

Other deferred credits and liabilities

622

643

'

'

'

'

'

29

'

'

'

'

'

'

'

'

Accounts Payable and Accrued Liabilities, Current

806

533

'

'

'

'

'

10

'

'

'

'

'

'

'

'

Proceeds from Sales of Business, Affiliate and Productive Assets

'

'

'

'

'

'

'

'

'

137.5

'

'

'

'

'

168

Impairment of Long-Lived Assets Held-for-use

'

'

26

'

'

'

'

'

'

'

'

'

'

'

'

'

Inventory Write-down

'

'

4

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from Asset Sale Held in Escrow

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$17

Divestiture_Transactions_and_D3

Divestiture Transactions and Discontinued Operations (Components of Discontinued Operations in Consolidated Statement of Income) (Details) (USD $)	12 Months Ended							3 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
						Merchant Generation	Merchant Generation	Merchant Generation
								Duck Creek Energy Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'		'		'	'	'	'
Operating revenues	$1,037		$1,047		$1,358	'	'	'
Operating expenses	-1,207	[1]	-3,474	[2]	-1,150	'	'	'
Operating income (loss)	-170		-2,427		208	'	'	'
Other income (loss)	-1		'		1	'	'	'
Interest charges	-39		-56		-64	'	'	'
Income (loss) before income taxes	-210		-2,483		145	'	'	'
Income tax (expense) benefit	-13		987		-56	'	'	'
Income (Loss) from Discontinued Operations, Net of Tax (Note 16)	-223		-1,496		89	'	'	'
Impairment of assets to be disposed of	'		'		'	$201	$1,950	$628
[1]	(a)Includes a $201 million pretax loss on disposal relating to the New AER divestiture.
[2]	(b)Includes a noncash pretax asset impairment charge of $628 million to reduce the carrying value of AERG’s Duck Creek energy center to its estimated fair value under held and used accounting guidance. In addition, includes a noncash pretax asset impairment charge of $1.95 billion to reduce the carrying values of all the AER coal and natural gas-fired energy centers, except the Joppa coal-fired energy center, to their estimated fair values, under held and used accounting guidance, as a result of the decision in December 2012 that Ameren intended to exit the Merchant Generation business.

Divestiture_Transactions_and_D4

Divestiture Transactions and Discontinued Operations (Components of Assets and Liabilities on Consolidated Balance Sheet) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
In Millions, unless otherwise specified
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'		'		'
Asset retirement obligations	$369		$349		'
Current assets of discontinued operations	'		'		'
Cash and cash equivalents	'		25		7
Accounts receivable and unbilled revenue	5		102		'
Materials and supplies	5		135		'
Mark-to-market derivative assets	'		102		'
Property and plant, net	142		748		'
Accumulated deferred income taxes, net	13	[1]	395	[1]	'
Other assets	'		104		'
Total current assets of discontinued operations	165		1,611		3,721
Current liabilities of discontinued operations	'		'		'
Accounts payable and other current obligations	5		141		'
Mark-to-market derivative liabilities	'		63		'
Long-term debt, net	'		824		'
Asset retirement obligations	40	[2]	97	[2]	'
Pension and other postretirement benefits	'		40		'
Other liabilities	'		28		'
Total current liabilities of discontinued operations	45		1,193		'
Accumulated other comprehensive income (loss)	'	[3]	19	[3]	'
Noncontrolling Interest	'	[4]	8	[4]	'
Electric Energy Inc	'		'		'
Current liabilities of discontinued operations	'		'		'
Percentage of EEI not owned by Ameren	'		20.00%		'
Shutdown Of Meredosia And Hutsonville Energy Centers [Member]	'		'		'
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'		'		'
Asset retirement obligations	$31		$26		'
[1]	(a)The December 31, 2013 balance primarily consists of deferred income tax assets related to the abandoned Meredosia and Hutsonville energy centers.
[2]	(b)Includes AROs associated with the abandoned Meredosia and Hutsonville energy centers of $31 million and $26 million at December 31, 2013, and 2012, respectively.
[3]	(c)Accumulated other comprehensive income related to discontinued operations included in “Accumulated other comprehensive loss” on Ameren’s December 31, 2012, consolidated balance sheet. This balance related to New AER assets and liabilities that were realized or removed from Ameren’s consolidated balance sheet either before or at the December 2, 2013 closing of the New AER divestiture.
[4]	(d)The 20% ownership interest of EEI not owned by Ameren was included in “Noncontrolling interests” on Ameren’s December 31, 2012, consolidated balance sheet. This noncontrolling interest was removed from Ameren’s consolidated balance sheet at the December 2, 2013 closing of the New AER divestiture.

Segment_Information_Details

Segment Information (Details) (USD $)

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

segment

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Assets of discontinued operations (Note 16)

$165

'

'

'

$1,611

'

'

'

$165

$1,611

$3,721

Number of reportable segments

'

'

'

'

'

'

'

'

2

'

'

External revenues

1,322

1,638

1,403

1,475

1,258

1,709

1,402

1,412

5,838

5,781

6,148

Depreciation and amortization

'

'

'

'

'

'

'

'

706

673

643

Interest Expense

'

'

'

'

'

'

'

'

398

392

387

Income taxes (benefit)

'

'

'

'

'

'

'

'

311

[1]

307

[1]

254

[1]

Net income (loss) attributable to Ameren Corporation

37

302

95

-145

-1,156

374

211

-403

289

-974

519

Income (Loss) from Continuing Operations Attributable to Parent

48

305

105

54

12

302

164

38

512

516

431

Capital expenditures

'

'

'

'

'

'

'

'

1,379

1,063

881

Total assets

21,042

'

'

'

22,230

'

'

'

21,042

22,230

'

Union Electric Company

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

External revenues

'

'

'

'

'

'

'

'

3,516

3,252

3,360

Revenue from Related Parties

'

'

'

'

'

'

'

'

25

20

23

Depreciation and amortization

'

'

'

'

'

'

'

'

454

440

408

Interest and dividend income

'

'

'

'

'

'

'

'

27

32

30

Interest Expense

'

'

'

'

'

'

'

'

210

223

209

Income taxes (benefit)

'

'

'

'

'

'

'

'

242

252

161

Net income (loss) attributable to Ameren Corporation

'

'

'

'

'

'

'

'

395

416

287

Capital expenditures

'

'

'

'

'

'

'

'

648

595

550

Total assets

12,904

'

'

'

13,043

'

'

'

12,904

13,043

12,757

Ameren Illinois Company

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

External revenues

'

'

'

'

'

'

'

'

2,307

2,524

2,784

Revenue from Related Parties

'

'

'

'

'

'

'

'

4

1

3

Depreciation and amortization

'

'

'

'

'

'

'

'

243

221

215

Interest and dividend income

'

'

'

'

'

'

'

'

2

0

1

Interest Expense

'

'

'

'

'

'

'

'

143

129

136

Income taxes (benefit)

'

'

'

'

'

'

'

'

110

94

127

Net income (loss) attributable to Ameren Corporation

'

'

'

'

'

'

'

'

160

141

193

Capital expenditures

'

'

'

'

'

'

'

'

701

442

351

Total assets

7,454

'

'

'

7,282

'

'

'

7,454

7,282

7,213

Other Segment

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

External revenues

'

'

'

'

'

'

'

'

15

5

4

Revenue from Related Parties

'

'

'

'

'

'

'

'

2

3

3

Depreciation and amortization

'

'

'

'

'

'

'

'

9

12

20

Interest and dividend income

'

'

'

'

'

'

'

'

1

'

'

Interest Expense

'

'

'

'

'

'

'

'

45

40

42

Income taxes (benefit)

'

'

'

'

'

'

'

'

-41

-39

-34

Net income (loss) attributable to Ameren Corporation

'

'

'

'

'

'

'

'

-43

-41

-49

Capital expenditures

'

'

'

'

'

'

'

'

30

[2]

26

[2]

-20

[2]

Total assets

752

'

'

'

1,228

'

'

'

752

1,228

1,211

Intersegment Elimination

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Revenue from Related Parties

'

'

'

'

'

'

'

'

-31

-24

-29

Interest and dividend income

'

'

'

'

'

'

'

'

'

'

'

Interest Expense

'

'

'

'

'

'

'

'

'

'

'

Total assets

-233

'

'

'

-934

'

'

'

-233

-934

-1,179

Segment, Continuing Operations

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

External revenues

'

'

'

'

'

'

'

'

5,838

5,781

6,148

Depreciation and amortization

'

'

'

'

'

'

'

'

706

673

643

Interest and dividend income

'

'

'

'

'

'

'

'

30

32

31

Interest Expense

'

'

'

'

'

'

'

'

398

392

387

Income taxes (benefit)

'

'

'

'

'

'

'

'

311

307

254

Income (Loss) from Continuing Operations Attributable to Parent

'

'

'

'

'

'

'

'

512

516

431

Capital expenditures

'

'

'

'

'

'

'

'

1,379

1,063

881

Total assets

20,877

[3]

'

'

'

20,619

[3]

'

'

'

20,877

[3]

20,619

[3]

20,002

[3]

Union Electric Company

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

External revenues

763

1,093

889

796

673

1,064

844

691

3,541

3,272

3,383

Revenue from Related Parties

'

'

'

'

'

'

'

'

25

20

23

Depreciation and amortization

'

'

'

'

'

'

'

'

454

440

408

Interest Expense

'

'

'

'

'

'

'

'

210

223

209

Income taxes (benefit)

'

'

'

'

'

'

'

'

242

252

161

Net income (loss) attributable to Ameren Corporation

33

239

85

41

16

237

144

22

398

419

290

Capital expenditures

'

'

'

'

'

'

'

'

648

595

550

Total assets

12,904

'

'

'

13,043

'

'

'

12,904

13,043

'

Ameren Illinois Company

'

'

'

'

'

'

'

'

'

'

'

Segment Reporting Information [Line Items]

'

'

'

'

'

'

'

'

'

'

'

External revenues

564

547

516

684

589

648

564

724

2,311

2,525

2,787

Revenue from Related Parties

'

'

'

'

'

'

'

'

4

1

3

Depreciation and amortization

'

'

'

'

'

'

'

'

243

221

215

Interest Expense

'

'

'

'

'

'

'

'

143

129

136

Income taxes (benefit)

'

'

'

'

'

'

'

'

110

94

127

Net income (loss) attributable to Ameren Corporation

22

77

32

32

12

71

33

28

163

144

196

Capital expenditures

'

'

'

'

'

'

'

'

701

442

351

Total assets

$7,454

'

'

'

$7,282

'

'

'

$7,454

$7,282

'

[1]

Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

[2]

Includes the elimination of intercompany transfers.

[3]

Excludes total assets from discontinued operations of $165 million, $1,611 million, and $3,721 million as of December 31, 2013, 2012, and 2011, respectively.

Selected_Quarterly_Information2

Selected Quarterly Information (Summary Of Selected Quarterly Information) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Quarterly Financial Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating revenues	$1,322,000,000	$1,638,000,000	$1,403,000,000	$1,475,000,000	$1,258,000,000	$1,709,000,000	$1,402,000,000	$1,412,000,000	$5,838,000,000	$5,781,000,000	$6,148,000,000
Operating Income	171,000,000	567,000,000	261,000,000	185,000,000	112,000,000	570,000,000	347,000,000	159,000,000	1,184,000,000	1,188,000,000	1,033,000,000
Net income (loss)	38,000,000	304,000,000	96,000,000	-143,000,000	-1,155,000,000	374,000,000	210,000,000	-403,000,000	295,000,000	-974,000,000	526,000,000
Net income attributable to Ameren Corporation - continuing operations	48,000,000	305,000,000	105,000,000	54,000,000	12,000,000	302,000,000	164,000,000	38,000,000	512,000,000	516,000,000	431,000,000
Net income (loss) attributable to Ameren Corporation - discontinued operations	-11,000,000	-3,000,000	-10,000,000	-199,000,000	-1,168,000,000	72,000,000	47,000,000	-441,000,000	223,000,000	1,490,000,000	-88,000,000
Net income (loss) attributable to Ameren Corporation	37,000,000	302,000,000	95,000,000	-145,000,000	-1,156,000,000	374,000,000	211,000,000	-403,000,000	289,000,000	-974,000,000	519,000,000
Impairment and other charges	'	'	'	'	'	'	'	'	'	'	'
Earnings per common share - basic - continuing operations	$0.19	$1.26	$0.44	$0.22	$0.05	$1.25	$0.67	$0.16	$2.11	$2.13	$1.79
Earnings (loss) per common share - basic - discontinued operations	($0.04)	($0.01)	($0.05)	($0.82)	($4.81)	$0.29	$0.20	($1.82)	($0.92)	($6.14)	$0.36
Earnings (loss) per common share - basic	$0.15	$1.25	$0.39	($0.60)	($4.76)	$1.54	$0.87	($1.66)	$1.19	($4.01)	$2.15
Earnings per common share - diluted - continuing operations	$0.19	$1.25	$0.44	$0.22	$0.05	$1.25	$0.67	$0.16	$2.10	$2.13	$1.79
Earnings (loss) per common share - diluted - discontinued operations	($0.04)	($0.01)	($0.05)	($0.82)	($4.81)	$0.29	$0.20	($1.82)	($0.92)	($6.14)	$0.36
Earnings (loss) per common share - diluted	$0.15	$1.24	$0.39	($0.60)	($4.76)	$1.54	$0.87	($1.66)	$1.18	($4.01)	$2.15
Union Electric Company	'	'	'	'	'	'	'	'	'	'	'
Selected Quarterly Financial Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating revenues	763,000,000	1,093,000,000	889,000,000	796,000,000	673,000,000	1,064,000,000	844,000,000	691,000,000	3,541,000,000	3,272,000,000	3,383,000,000
Operating Income	96,000,000	417,000,000	179,000,000	111,000,000	69,000,000	429,000,000	269,000,000	78,000,000	803,000,000	845,000,000	609,000,000
Net income (loss)	'	'	'	'	'	'	'	'	398,000,000	419,000,000	290,000,000
Net income (loss) attributable to Ameren Corporation	33,000,000	239,000,000	85,000,000	41,000,000	16,000,000	237,000,000	144,000,000	22,000,000	398,000,000	419,000,000	290,000,000
Net Income Available to Common Stockholder	33,000,000	238,000,000	84,000,000	40,000,000	16,000,000	236,000,000	143,000,000	21,000,000	395,000,000	416,000,000	287,000,000
Ameren Illinois Company	'	'	'	'	'	'	'	'	'	'	'
Selected Quarterly Financial Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Operating revenues	564,000,000	547,000,000	516,000,000	684,000,000	589,000,000	648,000,000	564,000,000	724,000,000	2,311,000,000	2,525,000,000	2,787,000,000
Operating Income	85,000,000	158,000,000	87,000,000	85,000,000	51,000,000	151,000,000	86,000,000	89,000,000	415,000,000	377,000,000	458,000,000
Net income (loss)	'	'	'	'	'	'	'	'	163,000,000	144,000,000	196,000,000
Net income (loss) attributable to Ameren Corporation	22,000,000	77,000,000	32,000,000	32,000,000	12,000,000	71,000,000	33,000,000	28,000,000	163,000,000	144,000,000	196,000,000
Net Income Available to Common Stockholder	21,000,000	77,000,000	31,000,000	31,000,000	11,000,000	71,000,000	32,000,000	27,000,000	160,000,000	141,000,000	193,000,000
Merchant Generation	'	'	'	'	'	'	'	'	'	'	'
Selected Quarterly Financial Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Impairment and other charges	'	'	'	'	'	'	'	'	'	$2,600,000,000	'

Schedule_I_Condensed_Financial1

Schedule I - Condensed Financial Information Of Parent (Statement of Income) (Details) (USD $)

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Condensed Financial Statements, Captions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating revenues

$1,322

$1,638

$1,403

$1,475

$1,258

$1,709

$1,402

$1,412

$5,838

$5,781

$6,148

Operating expenses

'

'

'

'

'

'

'

'

4,654

4,593

5,115

Operating Income

171

567

261

185

112

570

347

159

1,184

1,188

1,033

Interest income from affiliates

'

'

'

'

'

'

'

'

3

[1]

4

[1],[2]

3

[1]

Miscellaneous expense

'

'

'

'

'

'

'

'

26

[1]

37

[1]

23

[1]

Interest charges

'

'

'

'

'

'

'

'

398

392

387

Income taxes (benefit)

'

'

'

'

'

'

'

'

311

[1]

307

[1]

254

[1]

Net income attributable to Ameren Corporation - continuing operations

48

305

105

54

12

302

164

38

512

516

431

Net Income (Loss) Attributable to Ameren Corporation - Discontinued Operations

11

3

10

199

1,168

-72

-47

441

-223

-1,490

88

Net income (loss) attributable to Ameren Corporation

37

302

95

-145

-1,156

374

211

-403

289

-974

519

Comprehensive Income from Continuing Operations

'

'

'

'

'

'

'

'

'

'

'

Pension and other postretirement activity, net of income taxes (benefit)

'

'

'

'

'

'

'

'

30

-8

-19

Comprehensive Income (Loss) from Continuing Operations, Net of Tax, Portion Attributable to Parent

'

'

'

'

'

'

'

'

542

508

412

Other Comprehensive Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest

'

'

'

'

'

'

'

'

-18

58

-20

Comprehensive Income (Loss) from Discontinued Operations

'

'

'

'

'

'

'

'

-242

-1,440

74

Comprehensive Income (Loss) Attributable to Ameren Corporation

'

'

'

'

'

'

'

'

300

-932

486

Other Comprehensive Income (Loss), Taxes:

'

'

'

'

'

'

'

'

'

'

'

Pension and other postretirement activity, tax (benefit)

'

'

'

'

'

'

'

'

16

-6

-14

Parent Company

'

'

'

'

'

'

'

'

'

'

'

Condensed Financial Statements, Captions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Operating revenues

'

'

'

'

'

'

'

'

'

'

'

Operating expenses

'

'

'

'

'

'

'

'

26

17

13

Operating Income

'

'

'

'

'

'

'

'

-26

-17

-13

Equity in earnings of subsidiaries

'

'

'

'

'

'

'

'

546

546

464

Interest income from affiliates

'

'

'

'

'

'

'

'

3

3

5

Miscellaneous expense

'

'

'

'

'

'

'

'

5

4

4

Interest charges

'

'

'

'

'

'

'

'

42

39

41

Income taxes (benefit)

'

'

'

'

'

'

'

'

-36

-27

-20

Net income attributable to Ameren Corporation - continuing operations

'

'

'

'

'

'

'

'

512

516

431

Net Income (Loss) Attributable to Ameren Corporation - Discontinued Operations

'

'

'

'

'

'

'

'

-223

-1,490

88

Net income (loss) attributable to Ameren Corporation

'

'

'

'

'

'

'

'

289

-974

519

Comprehensive Income from Continuing Operations

'

'

'

'

'

'

'

'

'

'

'

Pension and other postretirement activity, net of income taxes (benefit)

'

'

'

'

'

'

'

'

30

-8

-19

Comprehensive Income (Loss) from Continuing Operations, Net of Tax, Portion Attributable to Parent

'

'

'

'

'

'

'

'

542

508

412

Other Comprehensive Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest

'

'

'

'

'

'

'

'

-19

50

-14

Comprehensive Income (Loss) from Discontinued Operations

'

'

'

'

'

'

'

'

-242

-1,440

74

Comprehensive Income (Loss) Attributable to Ameren Corporation

'

'

'

'

'

'

'

'

300

-932

486

Other Comprehensive Income (Loss), Taxes:

'

'

'

'

'

'

'

'

'

'

'

Pension and other postretirement activity, tax (benefit)

'

'

'

'

'

'

'

'

$16

($6)

($14)

[1]

Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

[2]

Includes interest income received in 2012 relating to a refund of charges included in an expired power purchase agreement with Entergy.

Schedule_I_Condensed_Financial2

Schedule I - Condensed Financial Information Of Parent (Balance Sheet) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Millions, unless otherwise specified
ASSETS	'	'	'	'
Cash and cash equivalents	$30	$184	$248	'
Accounts and notes receivable - affiliates	404	354	'	'
Miscellaneous accounts and notes receivable	196	71	'	'
Other current assets	85	98	'	'
Total current assets	1,972	3,596	'	'
Current accumulated deferred income taxes, net	106	170	'	'
Other non-current assets	698	667	'	'
TOTAL ASSETS	21,042	22,230	'	'
LIABILITIES AND EQUITY	'	'	'	'
Current maturities of long-term debt	534	355	'	'
Short-term debt	368	'	'	'
Accounts Payable and Accrued Liabilities, Current	806	533	'	'
Other current liabilities	194	168	'	'
Total current liabilities	2,461	2,686	'	'
Long-term debt	5,504	5,802	'	'
Other deferred credits and liabilities	622	643	'	'
Commitments and Contingencies	'	'	'	'
Retained earnings	907	1,006	'	'
Accumulated other comprehensive income (loss)	3	-8	'	'
Total equity	6,686	6,767	8,068	'
TOTAL LIABILITIES AND EQUITY	21,042	22,230	'	'
Parent Company	'	'	'	'
ASSETS	'	'	'	'
Cash and cash equivalents	11	23	3	4
Advances to money pool	334	316	'	'
Accounts and notes receivable - affiliates	27	31	'	'
Miscellaneous accounts and notes receivable	125	'	'	'
Other current assets	42	49	'	'
Total current assets	539	419	'	'
Investments in subsidiaries - continuing operations	6,336	6,315	'	'
Investments in subsidiaries - discontinued operations	-5	-353	'	'
Note receivable - affiliates	51	462	'	'
Current accumulated deferred income taxes, net	623	210	'	'
Other non-current assets	141	110	'	'
TOTAL ASSETS	7,685	7,163	'	'
LIABILITIES AND EQUITY	'	'	'	'
Current maturities of long-term debt	425	'	'	'
Short-term debt	368	'	'	'
Accounts Payable and Accrued Liabilities, Current	119	3	'	'
Accounts payable – affiliates	4	10	'	'
Other current liabilities	20	30	'	'
Total current liabilities	936	43	'	'
Long-term debt	'	424	'	'
Other deferred credits and liabilities	205	80	'	'
Total liabilities	1,141	547	'	'
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 242.6	2	2	'	'
Other paid-in capital, principally premium on common stock	5,632	5,616	'	'
Retained earnings	907	1,006	'	'
Accumulated other comprehensive income (loss)	3	-8	'	'
Total equity	6,544	6,616	'	'
TOTAL LIABILITIES AND EQUITY	$7,685	$7,163	'	'

Schedule_I_Condensed_Financial3

Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]	'	'	'
Net cash provided by operating activities	$1,693	$1,690	$1,878
Cash Flows From Investing Activities:	'	'	'
Other	2	2	15
Net cash used in investing activities	-1,723	-1,310	-1,048
Cash flows from financing activities:	'	'	'
Dividends on common stock	-388	-382	-375
Short-term debt and credit facility borrowings, net	368	-148	-481
Issuances:	'	'	'
Long-term debt	278	882	'
Common stock	'	'	65
Net cash provided by (used in) financing activities	-149	-426	-1,120
Net change in cash and cash equivalents	-179	-46	-290
Cash and cash equivalents at beginning of year	184	248	'
Cash and cash equivalents at end of year	30	184	248
Noncash financing activity – dividends on common stock	'	7	'
Parent Company	'	'	'
Condensed Financial Statements, Captions [Line Items]	'	'	'
Net cash provided by operating activities	453	532	804
Cash Flows From Investing Activities:	'	'	'
Money pool advances, net	-371	24	-276
Intercompany notes receivable, net	-23	-20	358
Investments in subsidiaries	-50	-2	-94
Return of investments	1	21	3
Other	-2	-5	-5
Net cash used in investing activities	-445	18	-14
Cash flows from financing activities:	'	'	'
Dividends on common stock	-388	-382	-375
Short-term debt and credit facility borrowings, net	368	-148	-481
Issuances:	'	'	'
Common stock	'	'	65
Net cash provided by (used in) financing activities	-20	-530	-791
Net change in cash and cash equivalents	-12	20	-1
Cash and cash equivalents at beginning of year	23	3	4
Cash and cash equivalents at end of year	11	23	3
Cash dividends received from consolidated subsidiaries	570	610	730
Noncash investing activity - divestiture	494	'	'
Noncash financing activity – dividends on common stock	'	($7)	'

Schedule_I_Condensed_Financial4

Schedule I - Condensed Financial Information Of Parent (Impairment and Other Charges) (Details) (USD $)	12 Months Ended		1 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2014
	Parent Company	Parent Company	New Ameren Energy Resources Company, LLC
	Merchant Generation	Merchant Generation
Impairment and Other Charges [Line Items]	'	'	'
Impairment charge on long-lived assets and related charges	$201	$1,880	'
Disposal Group, Including Discontinued Operation, Working Capital Adjustment, Period	'	'	'120 days

Schedule_II_Valuation_And_Qual1

Schedule II - Valuation And Qualifying Accounts (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Allowance For Doubtful Accounts	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Balance at Beginning of Period	$17		$20		$23
Charged to Costs and Expenses	35		30		41
Charged to Other Accounts	4	[1]	2	[1]	'	[1]
Deductions	38	[2]	35	[2]	44	[2]
Balance at End of Period	18		17		20
Valuation Allowance of Deferred Tax Assets	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Balance at Beginning of Period	2		1		1
Charged to Costs and Expenses	5		1		'
Charged to Other Accounts	'		'		'
Deductions	'		'		'
Balance at End of Period	7		2		1
Union Electric Company | Allowance For Doubtful Accounts	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Balance at Beginning of Period	5		7		8
Charged to Costs and Expenses	16		11		17
Charged to Other Accounts	'	[1]	'	[1]	'	[1]
Deductions	16	[2]	13	[2]	18	[2]
Balance at End of Period	5		5		7
Union Electric Company | Valuation Allowance of Deferred Tax Assets	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Balance at Beginning of Period	1		1		1
Charged to Costs and Expenses	'		'		'
Charged to Other Accounts	'		'		'
Deductions	'		'		'
Balance at End of Period	1		1		1
Ameren Illinois Company | Allowance For Doubtful Accounts	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Balance at Beginning of Period	12		13		13
Charged to Costs and Expenses	19		19		24
Charged to Other Accounts	4	[1]	2	[1]	'	[1]
Deductions	22	[2]	22	[2]	24	[2]
Balance at End of Period	13		12		13
Ameren Illinois Company | Valuation Allowance of Deferred Tax Assets	'		'		'
Valuation and Qualifying Accounts Disclosure [Line Items]	'		'		'
Balance at Beginning of Period	1		'		'
Charged to Costs and Expenses	'		1		'
Charged to Other Accounts	'		'		'
Deductions	'		'		'
Balance at End of Period	$1		$1		'
[1]	Uncollectible account reserve associated with receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act.
[2]	Uncollectible accounts charged off, less recoveries.