Consolidated Statement of Cash Flows (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012
Cash Flows From Operating Activities:
Net income (loss)	$ (47)		$ (193)
Loss from discontinued operations, net of taxes	209		394
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	334		314
Amortization of nuclear fuel	29		41
Amortization of debt issuance costs and premium/discounts	12		8
Deferred income taxes and investment tax credits, net	70		110
Allowance for equity funds used during construction	(16)	[1]	(17)	[1]
Stock-based compensation costs	14		12
Other	18		(6)
Changes in assets and liabilities:
Receivables	(92)		(16)
Materials and supplies	77		19
Accounts and wages payable	(75)		(138)
Taxes accrued	67		66
Assets, other	49		12
Liabilities, other	9		36
Pension and other postretirement benefits	36		23
Counterparty collateral, net	35		(1)
Net cash provided by operating activities - continuing operations	729		664
Net cash provided by operating activities - discontinued operations	39		97
Net cash provided by operating activities	768		761
Cash Flows From Investing Activities:
Capital expenditures	(575)		(485)
Nuclear fuel expenditures	(25)		(52)
Purchases of securities - nuclear decommissioning trust fund	(97)		(206)
Sales and maturities of securities - nuclear decommissioning trust fund	89		195
Other	2		(1)
Net cash used in investing activities - continuing operations	(606)		(549)
Net cash used in investing activities - discontinued operations	(31)		(64)
Net cash used in investing activities	(637)		(613)
Cash Flows From Financing Activities:
Dividends on common stock	(194)		(187)
Dividends paid to noncontrolling interest holders	(3)		(3)
Short-term debt, net	25		(118)
Advances received for construction	7		3
Net cash used in financing activities - continuing operations	(165)		(305)
Net cash used in financing activities - discontinued operations	0		0
Net cash used in financing activities	(165)		(305)
Net change in cash and cash equivalents	(34)		(157)
Cash and cash equivalents at beginning of year	184		248
Cash and cash equivalents at end of period	150		91
Noncash financing activity - dividends on common stock			(7)
Union Electric Company [Member]
Cash Flows From Operating Activities:
Net income (loss)	126		166
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	208		201
Amortization of nuclear fuel	29		41
Non cash Contested FAC	23		0
Amortization of debt issuance costs and premium/discounts	4		3
Deferred income taxes and investment tax credits, net	13		76
Allowance for equity funds used during construction	(14)		(15)
Changes in assets and liabilities:
Receivables	(155)		(65)
Materials and supplies	28		(43)
Accounts and wages payable	(119)		(164)
Taxes accrued	79		29
Assets, other	61		12
Liabilities, other	37		42
Pension and other postretirement benefits	18		18
Net cash provided by operating activities	338		301
Cash Flows From Investing Activities:
Capital expenditures	(273)		(299)
Nuclear fuel expenditures	(25)		(52)
Purchases of securities - nuclear decommissioning trust fund	(97)		(206)
Sales and maturities of securities - nuclear decommissioning trust fund	89		195
Money pool advances, net	24		0
Other	(3)		(5)
Net cash used in investing activities	(285)		(367)
Cash Flows From Financing Activities:
Dividends on common stock	(180)		(200)
Dividends on preferred stock	(2)		(2)
Money pool borrowings, net	0		67
Net cash used in financing activities	(182)		(135)
Net change in cash and cash equivalents	(129)		(201)
Cash and cash equivalents at beginning of year	148		201
Cash and cash equivalents at end of period	19		0
Ameren Illinois Company [Member]
Cash Flows From Operating Activities:
Net income (loss)	64		61
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	121		105
Amortization of debt issuance costs and premium/discounts	7		4
Deferred income taxes and investment tax credits, net	61		63
Other	(4)		(5)
Changes in assets and liabilities:
Receivables	62		62
Materials and supplies	50		59
Accounts and wages payable	46		13
Taxes accrued	(6)		(1)
Assets, other	(4)		(3)
Liabilities, other	(18)		3
Pension and other postretirement benefits	15		(5)
Counterparty collateral, net	32		4
Net cash provided by operating activities	426		360
Cash Flows From Investing Activities:
Capital expenditures	(283)		(184)
Money pool advances, net	0		(67)
Other	4		4
Net cash used in investing activities	(279)		(247)
Cash Flows From Financing Activities:
Dividends on common stock	(30)		(75)
Dividends on preferred stock	(2)		(2)
Money pool borrowings, net	(24)		0
Advances received for construction	7		3
Net cash used in financing activities	(49)		(74)
Net change in cash and cash equivalents	98		39
Cash and cash equivalents at beginning of year			21
Cash and cash equivalents at end of period	$ 98		$ 60

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