Consolidated Statement Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows From Operating Activities:
Net income	$ 834	$ 821	$ 529
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,002	938	876
Amortization of nuclear fuel	79	95	76
Amortization of debt issuance costs and premium/discounts	19	20	22
Deferred income taxes and investment tax credits, net	167	224	539
Allowance for equity funds used during construction	(28)	(36)	(24)
Share-based Compensation	20	20	17
Other	(14)	44	(10)
Changes in assets and liabilities:
Receivables	79	(24)	(53)
Inventories	(10)	39	17
Accounts and wages payable	(3)	(22)	32
Taxes accrued	(8)	(10)	55
Regulatory assets and liabilities	164	201	36
Assets, other	(59)	2	34
Liabilities, other	(33)	(117)	(7)
Pension and other postretirement benefits	(39)	(25)	(21)
Net cash provided by operating activities	2,170	2,170	2,118
Cash Flows From Investing Activities:
Capital expenditures	(2,411)	(2,286)	(2,132)
Nuclear fuel expenditures	(31)	(52)	(63)
Purchases of securities - nuclear decommissioning trust fund	(256)	(315)	(321)
Sales and maturities of securities - nuclear decommissioning trust fund	260	299	305
Purchase of bonds	(207)	0	0
Proceeds from sale of remarketed bonds	207	0	0
Other	3	18	7
Net cash used in investing activities	(2,435)	(2,336)	(2,204)
Cash Flows From Financing Activities:
Dividends on common stock	(472)	(451)	(431)
Dividends paid to noncontrolling interest holders	(6)	(6)	(6)
Short-term debt, net	(157)	112	(74)
Maturities of long-term debt	(580)	(841)	(681)
Issuances of Long-term debt	1,527	1,352	1,345
Issuances of common stock	68	74	0
Repurchases of common stock for stock-based compensation	0	0	(24)
Employee payroll taxes related to stock-based compensation	(29)	(19)	(15)
Debt issuance costs	17	14	11
Other	0	(2)	(1)
Net cash provided by financing activities	334	205	102
Net change in cash, cash equivalents, and restricted cash	69	39	16
Cash, cash equivalents, and restricted cash at beginning of year	107	68	52
Cash, cash equivalents, and restricted cash at end of year	176	107	68
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	367	387	370
Income taxes, net	13	21	(19)
Union Electric Company
Cash Flows From Operating Activities:
Net income	429	481	326
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	564	533	514
Amortization of nuclear fuel	79	95	76
Amortization of debt issuance costs and premium/discounts	5	6	6
Deferred income taxes and investment tax credits, net	(19)	(9)	82
Allowance for equity funds used during construction	(19)	(27)	(21)
Other	13	17	4
Changes in assets and liabilities:
Receivables	75	(32)	(46)
Inventories	(13)	30	18
Accounts and wages payable	16	(21)	27
Taxes accrued	(15)	(1)	(1)
Regulatory assets and liabilities	17	201	26
Assets, other	(28)	2	31
Liabilities, other	(32)	(13)	(23)
Pension and other postretirement benefits	(5)	(2)	(2)
Net cash provided by operating activities	1,067	1,260	1,017
Cash Flows From Investing Activities:
Capital expenditures	(1,076)	(914)	(773)
Nuclear fuel expenditures	(31)	(52)	(63)
Purchases of securities - nuclear decommissioning trust fund	(256)	(315)	(321)
Sales and maturities of securities - nuclear decommissioning trust fund	260	299	305
Purchase of bonds	(207)	0	0
Proceeds from sale of remarketed bonds	207	0	0
Money pool advances, net			161
Other	8	6	7
Net cash used in investing activities	(1,095)	(976)	(684)
Cash Flows From Financing Activities:
Dividends on common stock	(430)	(375)	(362)
Dividends on preferred stock	(3)	(3)	(3)
Short-term debt, net	179	16	39
Maturities of long-term debt	(580)	(384)	(431)
Issuances of Long-term debt	778	423	399
Debt issuance costs	9	5	3
Capital contribution from parent	124	45	30
Net cash provided by financing activities	59	(283)	(331)
Net change in cash, cash equivalents, and restricted cash	31	1	2
Cash, cash equivalents, and restricted cash at beginning of year	8	7	5
Cash, cash equivalents, and restricted cash at end of year	39	8	7
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	190	196	202
Income taxes, net	101	128	178
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	346	307	271
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	405	375	341
Amortization of debt issuance costs and premium/discounts	12	13	13
Deferred income taxes and investment tax credits, net	80	88	171
Allowance for equity funds used during construction	(9)	(9)	(3)
Other	7	11	0
Changes in assets and liabilities:
Receivables	11	0	(7)
Inventories	2	8	(1)
Accounts and wages payable	(19)	(13)	19
Taxes accrued	21	(13)	18
Regulatory assets and liabilities	155	1	16
Assets, other	(23)	(1)	(2)
Liabilities, other	(5)	(92)	3
Pension and other postretirement benefits	(30)	(25)	(14)
Net cash provided by operating activities	962	659	828
Cash Flows From Investing Activities:
Capital expenditures	(1,208)	(1,258)	(1,076)
Other	3	10	6
Net cash used in investing activities	(1,205)	(1,248)	(1,070)
Cash Flows From Financing Activities:
Dividends on preferred stock	(3)	(3)	(3)
Short-term debt, net	(19)	10	11
Maturities of long-term debt	0	(457)	(250)
Issuances of Long-term debt	299	929	496
Debt issuance costs	4	9	6
Capital contribution from parent	15	160	8
Other		(2)	(1)
Net cash provided by financing activities	288	628	255
Net change in cash, cash equivalents, and restricted cash	45	39	13
Cash, cash equivalents, and restricted cash at beginning of year	80	41	28
Cash, cash equivalents, and restricted cash at end of year	125	80	41
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	127	144	139
Income taxes, net	$ 4	$ 28	$ (22)