Consolidated Balance Sheet (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Current Assets:
Cash and cash equivalents	$ 522	$ 545
Accounts receivable - trade (less allowance for doubtful accounts)	575	517
Unbilled revenue	292	406
Miscellaneous accounts and notes receivable	147	214
Materials and supplies	734	707
Mark-to-market derivative assets	94	129
Current regulatory assets	184	267
Other current assets	132	109
Total current assets	2,680	2,894
Property and Plant, Net	17,873	17,853
Investments and Other Assets:
Nuclear decommissioning trust fund	330	337
Goodwill	411	411
Intangible assets	6	7
Regulatory assets	1,213	1,263
Other assets	843	750
Total investments and other assets	2,803	2,768
TOTAL ASSETS	23,356	23,515
Current Liabilities:
Current maturities of long-term debt	178	155
Short-term debt	350	269
Accounts and wages payable	410	651
Taxes accrued	161	63
Interest accrued	159	107
Customer deposits	98	100
Mark-to-market derivative liabilities	118	161
Current regulatory liabilities	123	99
Other current liabilities	251	283
Total current liabilities	1,848	1,888
Credit Facility Borrowings		460
Long-term Debt, Net	6,682	6,853
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	3,299	2,886
Accumulated deferred investment tax credits	81	90
Regulatory liabilities	1,464	1,319
Asset retirement obligations	439	475
Pension and other postretirement benefits	922	1,045
Other deferred credits and liabilities	469	615
Total deferred credits and other liabilities	6,674	6,430
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock	2	2
Other paid-in capital, principally premium on common stock	5,580	5,520
Retained earnings	2,440	2,225
Accumulated other comprehensive loss	(25)	(17)
Total stockholders' equity	7,997	7,730
Noncontrolling Interests	155	154
Total equity	8,152	7,884
TOTAL LIABILITIES AND EQUITY	23,356	23,515
Union Electric Company [Member]
Current Assets:
Cash and cash equivalents	356	202
Accounts receivable - trade (less allowance for doubtful accounts)	308	217
Accounts receivable - affiliates	1	6
Unbilled revenue	131	159
Miscellaneous accounts and notes receivable	35	116
Materials and supplies	337	341
Current regulatory assets	103	179
Other current assets	68	55
Total current assets	1,339	1,275
Property and Plant, Net	9,796	9,775
Investments and Other Assets:
Nuclear decommissioning trust fund	330	337
Intangible assets	5	2
Regulatory assets	694	694
Other assets	474	421
Total investments and other assets	1,503	1,454
TOTAL ASSETS	12,638	12,504
Current Liabilities:
Current maturities of long-term debt	178	5
Accounts and wages payable	160	326
Accounts payable - affiliates	48	75
Taxes accrued	131	76
Interest accrued	72	63
Current regulatory liabilities	55	23
Current accumulated deferred income taxes, net	19	43
Other current liabilities	82	89
Total current liabilities	745	700
Long-term Debt, Net	3,777	3,949
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	2,148	1,908
Accumulated deferred investment tax credits	71	78
Regulatory liabilities	804	766
Asset retirement obligations	334	363
Pension and other postretirement benefits	352	369
Other deferred credits and liabilities	172	218
Total deferred credits and other liabilities	3,881	3,702
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock	511	511
Other paid-in capital, principally premium on common stock	1,555	1,555
Preferred stock not subject to mandatory redemption	80	80
Retained earnings	2,089	2,007
Total stockholders' equity	4,235	4,153
TOTAL LIABILITIES AND EQUITY	12,638	12,504
Ameren Illinois Company [Member]
Current Assets:
Cash and cash equivalents	116	322
Accounts receivable - trade (less allowance for doubtful accounts)	194	230
Accounts receivable - affiliates	9	73
Unbilled revenue	122	205
Miscellaneous accounts and notes receivable	73	44
Materials and supplies	239	198
Current regulatory assets	247	260
Other current assets	108	106
Total current assets	1,108	1,438
Property and Plant, Net	4,699	4,576
Investments and Other Assets:
Tax receivable - Genco	61	72
Goodwill	411	411
Regulatory assets	571	747
Other assets	214	162
Total investments and other assets	1,257	1,392
TOTAL ASSETS	7,064	7,406
Current Liabilities:
Current maturities of long-term debt		150
Accounts and wages payable	135	182
Accounts payable - affiliates	58	82
Taxes accrued	12	26
Interest accrued	46	27
Customer deposits	80	83
Mark-to-market derivative liabilities	73	82
Mark-to-market derivative liabilities - affiliates	166	172
Environmental remediation	57	72
Current regulatory liabilities	68	76
Other current liabilities	58	63
Total current liabilities	753	1,015
Long-term Debt, Net	1,658	1,657
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	925	724
Accumulated deferred investment tax credits	7	8
Regulatory liabilities	660	553
Pension and other postretirement benefits	328	413
Other deferred credits and liabilities	231	460
Total deferred credits and other liabilities	2,151	2,158
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock
Other paid-in capital, principally premium on common stock	1,952	1,952
Preferred stock not subject to mandatory redemption	62	62
Retained earnings	471	542
Accumulated other comprehensive loss	17	20
Total stockholders' equity	2,502	2,576
TOTAL LIABILITIES AND EQUITY	7,064	7,406
Ameren Energy Generating Company [Member]
Current Assets:
Cash and cash equivalents	8	6
Advances to money pool	63	25
Accounts receivable - affiliates	82	126
Miscellaneous accounts and notes receivable	33	19
Materials and supplies	118	130
Mark-to-market derivative assets	10	26
Other current assets	8	4
Total current assets	322	336
Property and Plant, Net	2,219	2,248
Investments and Other Assets:
Intangible assets		3
Other assets	16	24
Total investments and other assets	16	27
TOTAL ASSETS	2,557	2,611
Current Liabilities:
Accounts and wages payable	58	62
Accounts payable - affiliates	9	23
Current portion of tax payable - Ameren Illinois	9	8
Taxes accrued	14	20
Interest accrued	27	13
Mark-to-market derivative liabilities	3	9
Mark-to-market derivative liabilities - affiliates		5
Current accumulated deferred income taxes, net	13	13
Other current liabilities	15	12
Total current liabilities	148	165
Credit Facility Borrowings		100
Long-term Debt, Net	824	824
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	313	253
Accumulated deferred investment tax credits	3	3
Tax payable - Ameren Illinois	61	72
Asset retirement obligations	69	74
Pension and other postretirement benefits	83	88
Other deferred credits and liabilities	14	23
Total deferred credits and other liabilities	543	513
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock
Other paid-in capital, principally premium on common stock	649	649
Retained earnings	422	393
Accumulated other comprehensive loss	(42)	(44)
Total stockholders' equity	1,029	998
Noncontrolling Interests	13	11
Total equity	1,042	1,009
TOTAL LIABILITIES AND EQUITY	$ 2,557	$ 2,611