Consolidated Statement Of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011
Cash Flows From Operating Activities:
Net income (loss)	$ (193)		$ 213
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Loss on asset impairments	628		2
(Gain) loss on sales of properties	(9)		(11)
Net mark-to-market (gain) loss on derivatives	11		(5)
Depreciation and amortization	373		373
Amortization of nuclear fuel	41		34
Amortization of debt issuance costs and premium/discounts	11		12
Deferred income taxes and investment tax credits, net	(100)		143
Allowance for equity funds used during construction	(17)	[1]	(15)	[1]
Other	8
Changes in assets and liabilities:
Receivables	(9)		23
Materials and supplies	27		55
Accounts and wages payable	(146)		(134)
Taxes accrued	75		76
Assets, other	11		82
Liabilities, other	72		(3)
Pension and other postretirement benefits	24		31
Counterparty collateral, net	(2)		23
Net cash provided by operating activities	805		899
Cash Flows From Investing Activities:
Capital expenditures	(565)		(507)
Nuclear fuel expenditures	(52)		(33)
Purchases of securities - nuclear decommissioning trust fund	(206)		(125)
Sales of securities - nuclear decommissioning trust fund	169		113
Proceeds from sales of properties	18		49
Other	(2)		9
Net cash used in investing activities	(638)		(494)
Cash Flows From Financing Activities:
Dividends on common stock	(187)		(186)
Dividends paid to noncontrolling interest holders	(3)		(3)
Short-term debt and credit facility repayments, net	(118)		(192)
Maturities of long-term debt			(150)
Generator advances received for construction	3
Repayments of generator advances received for construction			(73)
Issuances of common stock			32
Net cash used in financing activities	(305)		(572)
Net change in cash and cash equivalents	(138)		(167)
Cash and cash equivalents at beginning of year	255		545
Cash and cash equivalents at end of period	117		378
Noncash financing activity - dividends on common stock	(7)
Noncash investing activity - DOE settlement			9
Union Electric Company [Member]
Cash Flows From Operating Activities:
Net income (loss)	166		113
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Net mark-to-market (gain) loss on derivatives			1
Depreciation and amortization	201		184
Amortization of nuclear fuel	41		34
Amortization of debt issuance costs and premium/discounts	3		3
Deferred income taxes and investment tax credits, net	76		86
Allowance for equity funds used during construction	(15)		(14)
Other			(5)
Changes in assets and liabilities:
Receivables	(65)		(82)
Materials and supplies	(43)		(2)
Accounts and wages payable	(164)		(137)
Taxes accrued	29		58
Assets, other	12		76
Liabilities, other	68		23
Pension and other postretirement benefits	18		15
Net cash provided by operating activities	327		353
Cash Flows From Investing Activities:
Capital expenditures	(299)		(272)
Nuclear fuel expenditures	(52)		(33)
Purchases of securities - nuclear decommissioning trust fund	(206)		(125)
Sales of securities - nuclear decommissioning trust fund	169		113
Other	(5)		(3)
Net cash used in investing activities	(393)		(320)
Cash Flows From Financing Activities:
Dividends on common stock	(200)		(135)
Dividends on preferred stock	(2)		(2)
Money pool borrowings, net	67
Repayments of generator advances received for construction			(19)
Net cash used in financing activities	(135)		(156)
Net change in cash and cash equivalents	(201)		(123)
Cash and cash equivalents at beginning of year	201		202
Cash and cash equivalents at end of period			79
Noncash investing activity - DOE settlement			9
Ameren Illinois Company [Member]
Cash Flows From Operating Activities:
Net income (loss)	61		72
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	105		102
Amortization of debt issuance costs and premium/discounts	4		4
Deferred income taxes and investment tax credits, net	63		21
Other	(5)		(4)
Changes in assets and liabilities:
Receivables	62		110
Materials and supplies	59		53
Accounts and wages payable	13		(3)
Taxes accrued	(1)		21
Assets, other	(3)		15
Liabilities, other	3		(26)
Pension and other postretirement benefits	(5)		14
Counterparty collateral, net	4		22
Net cash provided by operating activities	360		401
Cash Flows From Investing Activities:
Capital expenditures	(184)		(174)
Returns of advances from ATXI for construction			49
Money pool advances, net	(67)
Other	4		4
Net cash used in investing activities	(247)		(121)
Cash Flows From Financing Activities:
Dividends on common stock	(75)		(150)
Dividends on preferred stock	(2)		(2)
Maturities of long-term debt			(150)
Generator advances received for construction	3
Repayments of generator advances received for construction			(53)
Capital contribution from parent			6
Net cash used in financing activities	(74)		(349)
Net change in cash and cash equivalents	39		(69)
Cash and cash equivalents at beginning of year	21		322
Cash and cash equivalents at end of period	60		253
Ameren Energy Generating Company [Member]
Cash Flows From Operating Activities:
Net income (loss)	(9)		35
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Gain) loss on sales of properties	1		(11)
Net mark-to-market (gain) loss on derivatives	14		(6)
Depreciation and amortization	46		51
Amortization of debt issuance costs and premium/discounts	1		1
Deferred income taxes and investment tax credits, net	(10)		26
Other	6		1
Changes in assets and liabilities:
Receivables	17		(15)
Materials and supplies	7		9
Accounts and wages payable	(8)		13
Taxes accrued			1
Assets, other	(2)		(2)
Liabilities, other	(5)		(12)
Pension and other postretirement benefits	2		(3)
Net cash provided by operating activities	60		88
Cash Flows From Investing Activities:
Capital expenditures	(79)		(84)
Proceeds from sales of properties	1		48
Money pool advances, net	36		25
Net cash used in investing activities	(42)		(11)
Cash Flows From Financing Activities:
Credit facility repayments, net			(100)
Capital contribution from parent			24
Net cash used in financing activities			(76)
Net change in cash and cash equivalents	18		1
Cash and cash equivalents at beginning of year	8		6
Cash and cash equivalents at end of period	$ 26		$ 7

[1] Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.