Consolidated Balance Sheet (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 150		$ 184
Accounts receivable - trade (less allowance for doubtful accounts)	425		354
Unbilled revenue	308		291
Miscellaneous accounts and notes receivable	75		71
Materials and supplies	511		570
Current regulatory assets	192		247
Current accumulated deferred income taxes, net	157		160
Other current assets	104		98
Current assets of discontinued operations	1,486		1,600
Total current assets	3,408		3,575
Property and Plant, Net	15,601		15,348
Investments and Other Assets:
Nuclear decommissioning trust fund	442		408
Goodwill	411		411
Intangible assets	18		14
Regulatory assets	1,742		1,786
Other assets	654		667
Total investments and other assets	3,267		3,286
TOTAL ASSETS	22,276		22,209
Current Liabilities:
Current maturities of long-term debt	884		355
Short-term debt	25
Accounts and wages payable	428		533
Taxes accrued	123		50
Interest accrued	100		89
Customer deposits	110		107
Mark-to-market derivative liabilities	75		92
Current regulatory liabilities	180		100
Other current liabilities	178		168
Current liabilities of discontinued operations	1,183		1,166
Total current liabilities	3,286		2,660
Long-term Debt, Net	5,274		5,802
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	3,348		3,166
Accumulated deferred investment tax credits	67		70
Regulatory liabilities	1,666		1,589
Asset retirement obligations	385		375
Pension and other postretirement benefits	1,140		1,138
Other deferred credits and liabilities	585		642
Total deferred credits and other liabilities	7,191		6,980
Commitments and Contingencies
Stockholders' Equity:
Common Stock	2		2
Other paid-in capital	5,619		5,616
Retained earnings	762		1,006
Accumulated other comprehensive income (loss)	(9)		(8)
Stockholder's equity	6,374		6,616
Noncontrolling Interest	151	[1]	151	[1]
Total equity	6,525		6,767
TOTAL LIABILITIES AND EQUITY	22,276		22,209
Union Electric Company [Member]
Current Assets:
Cash and cash equivalents	19		148
Advances to money pool			24
Accounts receivable - trade (less allowance for doubtful accounts)	229		161
Accounts receivable - affiliates	3		4
Unbilled revenue	225		145
Miscellaneous accounts and notes receivable	56		48
Materials and supplies	369		397
Current regulatory assets	132		163
Other current assets	100		69
Total current assets	1,133		1,159
Property and Plant, Net	10,264		10,161
Investments and Other Assets:
Nuclear decommissioning trust fund	442		408
Intangible assets	18		14
Regulatory assets	830		852
Other assets	444		449
Total investments and other assets	1,734		1,723
TOTAL ASSETS	13,131		13,043
Current Liabilities:
Current maturities of long-term debt	309		205
Accounts and wages payable	198		345
Accounts payable - affiliates	103		66
Taxes accrued	107		28
Interest accrued	73		60
Current regulatory liabilities	71		18
Other current liabilities	90		77
Total current liabilities	951		799
Long-term Debt, Net	3,697		3,801
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	2,474		2,443
Accumulated deferred investment tax credits	62		64
Regulatory liabilities	979		917
Asset retirement obligations	355		346
Pension and other postretirement benefits	465		461
Other deferred credits and liabilities	150		158
Total deferred credits and other liabilities	4,485		4,389
Commitments and Contingencies
Stockholders' Equity:
Common Stock	511		511
Other paid-in capital	1,556		1,556
Preferred stock not subject to mandatory redemption	80		80
Retained earnings	1,851		1,907
Stockholder's equity	3,998		4,054
TOTAL LIABILITIES AND EQUITY	13,131		13,043
Ameren Illinois Company [Member]
Current Assets:
Cash and cash equivalents	98
Accounts receivable - trade (less allowance for doubtful accounts)	185		182
Accounts receivable - affiliates	13		10
Unbilled revenue	83		146
Miscellaneous accounts and notes receivable	18		22
Materials and supplies	141		173
Current regulatory assets	61		84
Current accumulated deferred income taxes, net	82		85
Other current assets	29		47
Total current assets	710		749
Property and Plant, Net	5,216		5,052
Investments and Other Assets:
Tax receivable - Genco	38		39
Goodwill	411		411
Regulatory assets	908		934
Other assets	83		97
Total investments and other assets	1,440		1,481
TOTAL ASSETS	7,366		7,282
Current Liabilities:
Current maturities of long-term debt	150		150
Borrowings from money pool			24
Accounts and wages payable	184		146
Accounts payable - affiliates	91		86
Taxes accrued	13		18
Customer deposits	85		85
Mark-to-market derivative liabilities	55		77
Current environmental remediation	56		37
Current regulatory liabilities	110		82
Other current liabilities	79		92
Total current liabilities	823		797
Long-term Debt, Net	1,577		1,577
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes, net	1,082		1,025
Accumulated deferred investment tax credits	5		5
Regulatory liabilities	687		672
Pension and other postretirement benefits	416		406
Environmental remediation	196		216
Other deferred credits and liabilities	149		183
Total deferred credits and other liabilities	2,535		2,507
Commitments and Contingencies
Stockholders' Equity:
Common Stock	0		0
Other paid-in capital	1,965		1,965
Preferred stock not subject to mandatory redemption	62		62
Retained earnings	392		360
Accumulated other comprehensive income (loss)	12		14
Stockholder's equity	2,431		2,401
TOTAL LIABILITIES AND EQUITY	$ 7,366		$ 7,282

[1] Includes the 20% EEI ownership interest not owned by Ameren. The assets and liabilities of EEI were consolidated in Ameren’s balance sheet at a 100% ownership level and were included in “Current assets of discontinued operations” and “Current liabilities of discontinued operations.” The 20% ownership interest not owned by Ameren was included in “Noncontrolling interests” on Ameren’s June 30, 2013, and December 31, 2012 balance sheets. See Note 2 - Divestiture Transactions and Discontinued Operations for additional information.