Consolidated Statement Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash Flows From Operating Activities:
Net income	$ 529	$ 659	$ 636
(Income) Loss from discontinued operations, net of tax	0	0	(51)
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for Callaway construction and operating license	0	0	69
Depreciation and amortization	876	835	777
Amortization of nuclear fuel	76	88	97
Amortization of debt issuance costs and premium/discounts	22	22	22
Deferred income taxes and investment tax credits, net	539	386	369
Allowance for equity funds used during construction	(24)	(27)	(30)
Share-based Compensation	17	17	24
Other	(10)	4	(10)
Changes in assets and liabilities:
Receivables	(53)	(71)	83
Inventories	17	11	(14)
Accounts and wages payable	32	19	(2)
Taxes accrued	55	13	(22)
Regulatory assets and liabilities	36	215	94
Assets, other	20	(22)	46
Liabilities, other	(7)	(9)	(44)
Pension and other postretirement benefits	(21)	(16)	(9)
Net cash provided by operating activities - continuing operations	2,104	2,124	2,035
Net cash provided by operating activities - discontinued operations	0	(1)	(4)
Net cash provided by operating activities	2,104	2,123	2,031
Cash Flows From Investing Activities:
Capital expenditures	(2,132)	(2,076)	(1,917)
Nuclear fuel expenditures	(63)	(55)	(52)
Purchases of securities - nuclear decommissioning trust fund	(413)	(392)	(363)
Sales and maturities of securities - nuclear decommissioning trust fund	396	377	349
Other	7	5	32
Net cash used in investing activities - continuing operations	(2,205)	(2,141)	(1,951)
Net cash used in investing activities - discontinued operations	0	0	(25)
Net cash used in investing activities	(2,205)	(2,141)	(1,976)
Cash Flows From Financing Activities:
Dividends on common stock	(431)	(416)	(402)
Dividends paid to noncontrolling interest holders	(6)	(6)	(6)
Short-term debt, net	(74)	257	(413)
Maturities, redemptions, and repurchases of long-term debt	(681)	(395)	(120)
Issuances of Long-term debt	1,345	389	1,197
Capital issuance costs	(11)	(9)	(12)
Share-based payments	(39)	(83)	(12)
Other	(1)	(2)	0
Net cash provided by (used in) financing activities	102	(265)	232
Net change in cash and cash equivalents	1	(283)	287
Cash and cash equivalents at beginning of year	9	292	5
Cash and cash equivalents at end of year	10	9	292
Cash Paid (Refunded) During the Year:
Interest net of capitalized	370	358	335
Income taxes, net	(19)	(12)	(15)
Union Electric Company
Cash Flows From Operating Activities:
Net income	326	360	355
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for Callaway construction and operating license	0	0	69
Depreciation and amortization	514	506	476
Amortization of nuclear fuel	76	88	97
Amortization of debt issuance costs and premium/discounts	6	6	6
Deferred income taxes and investment tax credits, net	82	179	82
Allowance for equity funds used during construction	(21)	(23)	(22)
Other	4	5	2
Changes in assets and liabilities:
Receivables	(46)	5	72
Inventories	18	(4)	(39)
Accounts and wages payable	27	(18)	3
Taxes accrued	(1)	11	1
Regulatory assets and liabilities	26	84	117
Assets, other	30	(25)	26
Liabilities, other	(23)	(1)	4
Pension and other postretirement benefits	(2)	(4)	(2)
Net cash provided by operating activities	1,016	1,169	1,247
Cash Flows From Investing Activities:
Capital expenditures	(773)	(738)	(622)
Nuclear fuel expenditures	(63)	(55)	(52)
Purchases of securities - nuclear decommissioning trust fund	(413)	(392)	(363)
Sales and maturities of securities - nuclear decommissioning trust fund	396	377	349
Money pool advances, net	161	(125)	(36)
Other	7	(1)	0
Net cash used in investing activities	(685)	(934)	(724)
Cash Flows From Financing Activities:
Dividends on common stock	(362)	(355)	(575)
Dividends on preferred stock	(3)	(3)	(3)
Short-term debt, net	39	0	(97)
Maturities, redemptions, and repurchases of long-term debt	(431)	(266)	(120)
Issuances of Long-term debt	399	149	249
Capital issuance costs	(3)	(3)	(3)
Capital contribution from parent	30	44	224
Net cash provided by (used in) financing activities	(331)	(434)	(325)
Net change in cash and cash equivalents	0	(199)	198
Cash and cash equivalents at beginning of year	0	199	1
Cash and cash equivalents at end of year	0	0	199
Noncash Or Part Noncash Capital Contribution From Parent	0	0	38
Cash Paid (Refunded) During the Year:
Interest net of capitalized	202	209	212
Income taxes, net	178	27	72
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	271	255	217
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	341	318	292
Amortization of debt issuance costs and premium/discounts	13	14	14
Deferred income taxes and investment tax credits, net	171	154	221
Allowance for equity funds used during construction	(3)	(4)	(8)
Other	0	(1)	(14)
Changes in assets and liabilities:
Receivables	(7)	(72)	16
Inventories	(1)	15	25
Accounts and wages payable	19	12	37
Taxes accrued	18	1	(2)
Regulatory assets and liabilities	16	120	(26)
Assets, other	(15)	(3)	17
Liabilities, other	3	(5)	(27)
Pension and other postretirement benefits	(14)	(8)	(4)
Counterparty collateral, net	0	3	(3)
Net cash provided by operating activities	815	803	763
Cash Flows From Investing Activities:
Capital expenditures	(1,076)	(924)	(918)
Other	6	6	5
Net cash used in investing activities	(1,070)	(918)	(913)
Cash Flows From Financing Activities:
Dividends on common stock	0	(110)	0
Dividends on preferred stock	(3)	(3)	(3)
Short-term debt, net	11	51	(32)
Money pool borrowings, net	0	0	(15)
Maturities, redemptions, and repurchases of long-term debt	(250)	(129)	0
Issuances of Long-term debt	496	240	248
Capital issuance costs	(6)	(4)	(3)
Capital contribution from parent	8	0	25
Other	(1)	(1)	0
Net cash provided by (used in) financing activities	255	44	220
Net change in cash and cash equivalents	0	(71)	70
Cash and cash equivalents at beginning of year	0	71	1
Cash and cash equivalents at end of year	0	0	71
Cash Paid (Refunded) During the Year:
Interest net of capitalized	139	127	120
Income taxes, net	$ (22)	$ 8	$ (113)