Consolidated Balance Sheet (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Current Assets:
Cash and cash equivalents	$ 378	$ 545
Accounts receivable - trade (less allowance for doubtful accounts)	507	500
Unbilled revenue	368	406
Miscellaneous accounts and notes receivable	249	231
Materials and supplies	654	707
Mark-to-market derivative assets	159	129
Current regulatory assets	184	267
Other current assets	104	109
Total current assets	2,603	2,894
Property and Plant, Net	17,945	17,853
Investments and Other Assets:
Nuclear decommissioning trust fund	356	337
Goodwill	411	411
Intangible assets	4	7
Regulatory assets	1,224	1,263
Other assets	848	750
Regulated Entity, Other Assets, Noncurrent, Total	2,843	2,768
TOTAL ASSETS	23,391	23,515
Current Liabilities:
Current maturities of long-term debt	5	155
Short-term debt	337	269
Accounts and wages payable	482	651
Taxes accrued	139	63
Interest accrued	107	107
Customer deposits	100	100
Mark-to-market derivative liabilities	135	161
Current regulatory liabilities	160	99
Other current liabilities	262	283
Total current liabilities	1,727	1,888
Credit Facility Borrowings	200	460
Long-term Debt, Net	6,854	6,853
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	3,121	2,886
Accumulated deferred investment tax credits	87	90
Regulatory liabilities	1,424	1,319
Asset retirement obligations	487	475
Pension and other postretirement benefits	1,067	1,045
Other deferred credits and liabilities	481	615
Total deferred credits and other liabilities	6,667	6,430
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock	2	2
Other paid-in capital	5,559	5,520
Retained earnings	2,248	2,225
Accumulated other comprehensive loss	(21)	(17)
Total stockholders' equity	7,788	7,730
Noncontrolling Interests	155	154
Total equity	7,943	7,884
TOTAL LIABILITIES AND EQUITY	23,391	23,515
Union Electric Company [Member]
Current Assets:
Cash and cash equivalents	79	202
Accounts receivable - trade (less allowance for doubtful accounts)	236	217
Accounts receivable - affiliates	10	6
Unbilled revenue	200	159
Miscellaneous accounts and notes receivable	71	116
Materials and supplies	343	341
Mark-to-market derivative assets	58	35
Current regulatory assets	114	179
Other current assets	14	20
Total current assets	1,125	1,275
Property and Plant, Net	9,862	9,775
Investments and Other Assets:
Nuclear decommissioning trust fund	356	337
Intangible assets	4	2
Regulatory assets	691	694
Other assets	489	421
Regulated Entity, Other Assets, Noncurrent, Total	1,540	1,454
TOTAL ASSETS	12,527	12,504
Current Liabilities:
Current maturities of long-term debt	5	5
Accounts and wages payable	179	326
Accounts payable - affiliates	55	75
Taxes accrued	134	76
Interest accrued	73	63
Current accumulated deferred income taxes, net	18	43
Current regulatory liabilities	70	23
Other current liabilities	90	89
Total current liabilities	624	700
Long-term Debt, Net	3,949	3,949
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	2,027	1,908
Accumulated deferred investment tax credits	76	78
Regulatory liabilities	801	766
Asset retirement obligations	373	363
Pension and other postretirement benefits	371	369
Other deferred credits and liabilities	176	218
Total deferred credits and other liabilities	3,824	3,702
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock	511	511
Other paid-in capital	1,555	1,555
Preferred stock not subject to mandatory redemption	80	80
Retained earnings	1,984	2,007
Total stockholders' equity	4,130	4,153
TOTAL LIABILITIES AND EQUITY	12,527	12,504
Ameren Illinois [Member]
Current Assets:
Cash and cash equivalents	253	322
Accounts receivable - trade (less allowance for doubtful accounts)	197	230
Accounts receivable - affiliates	21	73
Unbilled revenue	129	205
Miscellaneous accounts and notes receivable	104	44
Materials and supplies	145	198
Current regulatory assets	243	260
Other current assets	109	106
Total current assets	1,201	1,438
Property and Plant, Net	4,657	4,576
Investments and Other Assets:
Tax receivable - Genco	64	72
Goodwill	411	411
Regulatory assets	628	747
Other assets	193	162
Regulated Entity, Other Assets, Noncurrent, Total	1,296	1,392
TOTAL ASSETS	7,154	7,406
Current Liabilities:
Current maturities of long-term debt		150
Accounts and wages payable	185	182
Accounts payable - affiliates	65	82
Taxes accrued	47	26
Customer deposits	82	83
Mark-to-market derivative liabilities	64	82
Mark-to-market derivative liabilities - affiliates	173	172
Environmental remediation	55	72
Current regulatory liabilities	90	76
Other current liabilities	77	90
Total current liabilities	838	1,015
Long-term Debt, Net	1,658	1,657
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	807	724
Accumulated deferred investment tax credits	7	8
Regulatory liabilities	623	553
Pension and other postretirement benefits	446	413
Other deferred credits and liabilities	282	460
Total deferred credits and other liabilities	2,165	2,158
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock
Other paid-in capital	1,952	1,952
Preferred stock not subject to mandatory redemption	62	62
Retained earnings	461	542
Accumulated other comprehensive loss	18	20
Total stockholders' equity	2,493	2,576
TOTAL LIABILITIES AND EQUITY	7,154	7,406
Ameren Energy Generating Company [Member]
Current Assets:
Cash and cash equivalents	7	6
Advances to money pool		25
Accounts receivable - affiliates	98	126
Miscellaneous accounts and notes receivable	54	19
Materials and supplies	121	130
Mark-to-market derivative assets	20	26
Other current assets	10	4
Total current assets	310	336
Property and Plant, Net	2,237	2,248
Investments and Other Assets:
Intangible assets		3
Other assets	22	24
TOTAL ASSETS	2,569	2,611
Current Liabilities:
Accounts and wages payable	64	62
Accounts payable - affiliates	25	23
Current portion of tax payable - Ameren Illinois	11	8
Taxes accrued	21	20
Interest accrued	13	13
Mark-to-market derivative liabilities	5	9
Mark-to-market derivative liabilities - affiliates	1	5
Current accumulated deferred income taxes, net	17	13
Other current liabilities	10	12
Total current liabilities	167	165
Credit Facility Borrowings		100
Long-term Debt, Net	824	824
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	290	253
Accumulated deferred investment tax credits	3	3
Tax payable - Ameren Illinois	64	72
Asset retirement obligations	75	74
Pension and other postretirement benefits	84	88
Other deferred credits and liabilities	17	23
Total deferred credits and other liabilities	533	513
Commitments and Contingencies (Notes 2, 8, 9 and 10)
Stockholders' Equity:
Common stock
Other paid-in capital	649	649
Retained earnings	427	393
Accumulated other comprehensive loss	(43)	(44)
Total stockholders' equity	1,033	998
Noncontrolling Interests	12	11
Total equity	1,045	1,009
TOTAL LIABILITIES AND EQUITY	$ 2,569	$ 2,611