Ameren (AEE) 10-K 23 Feb 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Jan. 31, 2022	Jun. 30, 2021
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	1-14756
Entity Registrant Name	Ameren Corporation
Entity Tax Identification Number	43-1723446
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol(s)	AEE
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Emerging growth company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 20,481,306,104
Entity Common Stock, Shares Outstanding		257,724,783
Documents Incorporated by Reference	Portions of the definitive proxy statement of Ameren Corporation and portions of the definitive information statements of Union Electric Company and Ameren Illinois Company for the 2022 annual meetings of shareholders are incorporated by reference into Part III of this Form 10-K.
Entity Central Index Key	0001002910
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
Union Electric Company
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
Entity File Number	1-2967
Entity Registrant Name	Union Electric Company
Entity Tax Identification Number	43-0559760
Entity Incorporation, State or Country Code	MO
Entity Address, Address Line One	1901 Chouteau Avenue
Entity Address, City or Town	St. Louis
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63103
City Area Code	(314)
Local Phone Number	621-3222
Title of 12(g) Security	Preferred Stock, cumulative, no par value, stated value $100 per share
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Emerging growth company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		102,123,834
Entity Central Index Key	0000100826
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
No Trading Symbol Flag	true
Ameren Illinois Company
Entity Information [Line Items]
Current Fiscal Year End Date	--12-31
Entity File Number	1-3672
Entity Registrant Name	Ameren Illinois Company
Entity Tax Identification Number	37-0211380
Entity Incorporation, State or Country Code	IL
Entity Address, Address Line One	10 Executive Drive
Entity Address, City or Town	Collinsville
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	62234
City Area Code	(618)
Local Phone Number	343-8150
Title of 12(g) Security	Preferred Stock, cumulative, $100 par value
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Emerging growth company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		25,452,373
Entity Central Index Key	0000018654
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false
No Trading Symbol Flag	true

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Auditor [Line Items]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	St. Louis, Missouri
Auditor Firm ID	238
Union Electric Company
Auditor [Line Items]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	St. Louis, Missouri
Auditor Firm ID	238
Ameren Illinois Company
Auditor [Line Items]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	St. Louis, Missouri
Auditor Firm ID	238

Consolidated Statement Of Incom

Consolidated Statement Of Income (Loss) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Revenues:
Operating revenues	$ 6,394	$ 5,794	$ 5,910
Operating Expenses:
Fuel	581	490	535
Purchased power	606	513	556
Natural gas purchased for resale	442	272	331
Other operations and maintenance	1,774	1,661	1,745
Depreciation and amortization	1,146	1,075	995
Taxes other than income taxes	512	483	481
Total operating expenses	5,061	4,494	4,643
Operating Income	1,333	1,300	1,267
Other Income, Net	202	151	130
Interest Charges	383	419	381
Income Before Income Taxes	1,152	1,032	1,016
Income Taxes	157	155	182
Net Income	995	877	834
Less: Net Income Attributable to Noncontrolling Interests	5	6	6
Net Income Attributable to Ameren Common Shareholders	990	871	828
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	14	16	5
Comprehensive Income	1,009	893	839
Less: Comprehensive Income Attributable to Noncontrolling Interests	5	6	6
Comprehensive Income Attributable to Ameren Common Shareholders	$ 1,004	$ 887	$ 833
Earnings per Common Share – Basic
Earnings per Common Share – Basic	$ 3.86	$ 3.53	$ 3.37
Earnings per Common Share – Diluted
Earnings per Common Share – Diluted	$ 3.84	$ 3.50	$ 3.35
Weighted-average Common Shares Outstanding – Basic	256.3	247	245.6
Weighted-average Common Shares Outstanding – Diluted	257.6	248.7	247.1
Union Electric Company
Operating Revenues:
Operating revenues	$ 3,353	$ 3,109	$ 3,243
Operating Expenses:
Fuel	581	490	535
Purchased power	227	171	193
Natural gas purchased for resale	60	43	53
Other operations and maintenance	948	886	960
Depreciation and amortization	632	604	556
Taxes other than income taxes	343	328	329
Total operating expenses	2,791	2,522	2,626
Operating Income	562	587	617
Other Income, Net	99	76	58
Interest Charges	137	190	178
Income Before Income Taxes	524	473	497
Income Taxes	3	34	68
Net Income	521	439	429
Preferred Stock Dividends	3	3	3
Net Income Attributable to Ameren Common Shareholders	518	436	426
Ameren Illinois Company
Operating Revenues:
Operating revenues	2,895	2,535	2,527
Operating Expenses:
Purchased power	400	355	368
Natural gas purchased for resale	382	229	278
Other operations and maintenance	820	775	782
Depreciation and amortization	472	434	406
Taxes other than income taxes	153	140	143
Total operating expenses	2,227	1,933	1,977
Operating Income	668	602	550
Other Income, Net	66	59	53
Interest Charges	164	155	147
Income Before Income Taxes	570	506	456
Income Taxes	143	124	110
Net Income	427	382	346
Preferred Stock Dividends	2	3	3
Net Income Attributable to Ameren Common Shareholders	425	379	343
Electric
Operating Revenues:
Operating revenues	5,297	4,911	4,981
Electric | Union Electric Company
Operating Revenues:
Operating revenues	3,212	2,984	3,109
Electric | Ameren Illinois Company
Operating Revenues:
Operating revenues	1,938	1,775	1,730
Natural gas
Operating Revenues:
Operating revenues	1,097	883	929
Natural gas | Union Electric Company
Operating Revenues:
Operating revenues	141	125	134
Natural gas | Ameren Illinois Company
Operating Revenues:
Operating revenues	$ 957	$ 760	$ 797

Consolidated Statement Of Inc_2

Consolidated Statement Of Income (Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Pension and other postretirement benefit plan activity, tax (benefit)	$ 4	$ 5	$ 1

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 8	$ 139
Accounts receivable - trade (less allowance for doubtful accounts)	434	415
Unbilled revenue	301	269
Miscellaneous accounts receivable	85	65
Inventories	592	521
Current regulatory assets	319	109
Other current assets	229	135
Total current assets	1,968	1,653
Property, Plant, and Equipment, Net	29,261	26,807
Investments and Other Assets:
Nuclear decommissioning trust fund	1,159	982
Goodwill	411	411
Regulatory assets	1,289	1,100
Pension and other postretirement benefits	756	288
Other assets	891	789
Total investments and other assets	4,506	3,570
TOTAL ASSETS	35,735	32,030
Current Liabilities:
Current maturities of long-term debt	505	8
Short-term debt	545	490
Accounts and wages payable	1,095	958
Interest accrued	123	114
Current regulatory liabilities	113	121
Other current liabilities	445	489
Total current liabilities	2,826	2,180
Long-term Debt, Net	12,562	11,078
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	3,499	3,211
Regulatory liabilities	5,848	5,282
Asset retirement obligations	757	696
Other deferred credits and liabilities	414	503
Total deferred credits and other liabilities	10,518	9,692
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	3	3
Other paid-in capital, principally premium on common stock	6,502	6,179
Retained earnings	3,182	2,757
Accumulated other comprehensive income (loss)	13	(1)
Total shareholders' equity	9,700	8,938
Noncontrolling Interests	129	142
Total equity	9,829	9,080
TOTAL LIABILITIES AND EQUITY	$ 35,735	$ 32,030

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable - trade, allowance for doubtful accounts	$ 29	$ 50
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	257,700,000	253,300,000	246,200,000	244,500,000

Consolidated Balance Sheet - UE

Consolidated Balance Sheet - UE - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 8	$ 139
Accounts receivable - trade (less allowance for doubtful accounts)	434	415
Unbilled revenue	301	269
Miscellaneous accounts receivable	85	65
Inventories	592	521
Current regulatory assets	319	109
Other current assets	229	135
Total current assets	1,968	1,653
Property, Plant, and Equipment, Net	29,261	26,807
Investments and Other Assets:
Nuclear decommissioning trust fund	1,159	982
Regulatory assets	1,289	1,100
Pension and other postretirement benefits	756	288
Other assets	891	789
Total investments and other assets	4,506	3,570
TOTAL ASSETS	35,735	32,030
Current Liabilities:
Current maturities of long-term debt	505	8
Short-term debt	545	490
Accounts and wages payable	1,095	958
Interest accrued	123	114
Current asset retirement obligations	7	60
Other current liabilities	445	489
Total current liabilities	2,826	2,180
Long-term Debt, Net	12,562	11,078
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	3,499	3,211
Regulatory liabilities	5,848	5,282
Asset retirement obligations	757	696
Other deferred credits and liabilities	414	503
Total deferred credits and other liabilities	10,518	9,692
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	3	3
Other paid-in capital, principally premium on common stock	6,502	6,179
Retained earnings	3,182	2,757
Total shareholders' equity	9,700	8,938
TOTAL LIABILITIES AND EQUITY	35,735	32,030
Union Electric Company
Current Assets:
Cash and cash equivalents	0	136
Advances to money pool	0	139
Accounts receivable - trade (less allowance for doubtful accounts)	190	166
Accounts receivable – affiliates	44	57
Unbilled revenue	142	133
Miscellaneous accounts receivable	71	36
Inventories	419	386
Current regulatory assets	127	60
Current collateral assets	66	11
Other current assets	76	68
Total current assets	1,135	1,192
Property, Plant, and Equipment, Net	15,296	13,879
Investments and Other Assets:
Nuclear decommissioning trust fund	1,159	982
Regulatory assets	523	347
Pension and other postretirement benefits	208	60
Other assets	401	323
Total investments and other assets	2,291	1,712
TOTAL ASSETS	18,722	16,783
Current Liabilities:
Current maturities of long-term debt	55	8
Short-term debt	165	0
Accounts and wages payable	631	501
Accounts payable – affiliates	46	46
Taxes accrued	34	42
Interest accrued	60	53
Current asset retirement obligations	7	60
Other current liabilities	219	123
Total current liabilities	1,217	833
Long-term Debt, Net	5,564	5,096
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	1,852	1,742
Regulatory liabilities	3,354	3,110
Asset retirement obligations	753	691
Other deferred credits and liabilities	71	101
Total deferred credits and other liabilities	6,030	5,644
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	511	511
Other paid-in capital, principally premium on common stock	2,725	2,518
Preferred stock	80	80
Retained earnings	2,595	2,101
Total shareholders' equity	5,911	5,210
TOTAL LIABILITIES AND EQUITY	$ 18,722	$ 16,783

Consolidated Balance Sheet - _2

Consolidated Balance Sheet - UE (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounts receivable - trade, allowance for doubtful accounts	$ 29	$ 50
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	257,700,000	253,300,000
Union Electric Company
Accounts receivable - trade, allowance for doubtful accounts	$ 13	$ 16
Common Stock, No Par Value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized	150,000,000	150,000,000
Common Stock, Shares, Outstanding	102,100,000	102,100,000

Consolidated Balance Sheet - AI

Consolidated Balance Sheet - AIC - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 8	$ 139
Accounts receivable - trade (less allowance for doubtful accounts)	434	415
Unbilled revenue	301	269
Miscellaneous accounts receivable	85	65
Inventories	592	521
Current regulatory assets	319	109
Other current assets	229	135
Total current assets	1,968	1,653
Property, Plant, and Equipment, Net	29,261	26,807
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	1,289	1,100
Pension and other postretirement benefits	756	288
Other assets	891	789
Total investments and other assets	4,506	3,570
TOTAL ASSETS	35,735	32,030
Current Liabilities:
Current maturities of long-term debt	505	8
Short-term debt	545	490
Accounts and wages payable	1,095	958
Current regulatory liabilities	113	121
Other current liabilities	445	489
Total current liabilities	2,826	2,180
Long-term Debt, Net	12,562	11,078
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	3,499	3,211
Regulatory liabilities	5,848	5,282
Other deferred credits and liabilities	414	503
Total deferred credits and other liabilities	10,518	9,692
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	3	3
Other paid-in capital, principally premium on common stock	6,502	6,179
Retained earnings	3,182	2,757
Total shareholders' equity	9,700	8,938
TOTAL LIABILITIES AND EQUITY	35,735	32,030
Ameren Illinois Company
Current Assets:
Cash and cash equivalents	0	0
Accounts receivable - trade (less allowance for doubtful accounts)	228	234
Accounts receivable – affiliates	24	64
Unbilled revenue	159	136
Miscellaneous accounts receivable	1	12
Inventories	173	135
Current regulatory assets	180	37
Other current assets	58	29
Total current assets	823	647
Property, Plant, and Equipment, Net	12,223	11,201
Investments and Other Assets:
Goodwill	411	411
Regulatory assets	752	742
Pension and other postretirement benefits	427	280
Other assets	399	254
Total investments and other assets	1,989	1,687
TOTAL ASSETS	15,035	13,535
Current Liabilities:
Current maturities of long-term debt	400	0
Short-term debt	103	0
Borrowings from money pool	0	19
Accounts and wages payable	361	363
Accounts payable – affiliates	64	51
Customer deposits	52	74
Current regulatory liabilities	54	88
Other current liabilities	199	221
Total current liabilities	1,233	816
Long-term Debt, Net	3,992	3,946
Deferred Credits and Other Liabilities:
Accumulated deferred income taxes and investment tax credits, net	1,558	1,367
Regulatory liabilities	2,374	2,063
Other deferred credits and liabilities	238	377
Total deferred credits and other liabilities	4,170	3,807
Commitments and Contingencies (Notes 2, 9, and 14)
Shareholders' Equity:
Common stock	0	0
Other paid-in capital, principally premium on common stock	2,914	2,652
Preferred stock	49	62
Retained earnings	2,677	2,252
Total shareholders' equity	5,640	4,966
TOTAL LIABILITIES AND EQUITY	$ 15,035	$ 13,535

Consolidated Balance Sheet - _3

Consolidated Balance Sheet - AIC (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounts receivable - trade, allowance for doubtful accounts	$ 29	$ 50
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	257,700,000	253,300,000
Ameren Illinois Company
Accounts receivable - trade, allowance for doubtful accounts	$ 16	$ 34
Common Stock, No Par Value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	45,000,000	45,000,000
Common Stock, Shares, Outstanding	25,500,000	25,500,000

Consolidated Statement Of Cash

Consolidated Statement Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash Flows From Operating Activities:
Net income	$ 995	$ 877	$ 834
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	1,219	1,085	1,002
Amortization of nuclear fuel	58	68	79
Amortization of debt issuance costs and premium/discounts	23	22	19
Deferred income taxes and investment tax credits, net	156	148	167
Allowance for equity funds used during construction	(43)	(32)	(28)
Stock-based compensation costs	22	21	20
Other	19	22	(14)
Changes in assets and liabilities:
Receivables	(74)	(47)	79
Inventories	(71)	(25)	(10)
Accounts and wages payable	28	40	(3)
Taxes accrued	1	34	(8)
Regulatory assets and liabilities	(439)	(254)	164
Assets, other	(126)	(83)	(59)
Liabilities, other	(74)	(111)	(33)
Pension and other postretirement benefits	(33)	(38)	(39)
Net cash provided by operating activities	1,661	1,727	2,170
Cash Flows From Investing Activities:
Capital expenditures	(2,954)	(2,669)	(2,411)
Wind generation expenditures	(525)	(564)	0
Nuclear fuel expenditures	(44)	(66)	(31)
Purchases of securities – nuclear decommissioning trust fund	(452)	(224)	(256)
Proceeds from sales and maturities	439	183	260
Purchase of bonds	0	0	(207)
Proceeds from sale of remarketed bonds	0	0	207
Other	8	11	3
Net cash used in investing activities	(3,528)	(3,329)	(2,435)
Cash Flows From Financing Activities:
Dividends on common stock	(565)	(494)	(472)
Dividends paid to noncontrolling interest holders	(5)	(6)	(6)
Short-term debt, net	55	50	(157)
Maturities of long-term debt	(8)	(442)	(580)
Issuances of long-term debt	1,997	2,183	1,527
Issuances of common stock	308	476	68
Redemptions of Ameren Illinois preferred stock	(13)	0	0
Employee payroll taxes related to stock-based compensation	(17)	(20)	(29)
Debt issuance costs	(18)	(20)	(17)
Other	(13)	0	0
Net cash provided by financing activities	1,721	1,727	334
Net change in cash, cash equivalents, and restricted cash	(146)	125	69
Cash, cash equivalents, and restricted cash at beginning of year	301	176	107
Cash, cash equivalents, and restricted cash at end of year	155	301	176
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	426	383	367
Income taxes, net	(1)	13	13
Union Electric Company
Cash Flows From Operating Activities:
Net income	521	439	429
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	704	613	564
Amortization of nuclear fuel	58	68	79
Amortization of debt issuance costs and premium/discounts	6	6	5
Deferred income taxes and investment tax credits, net	3	17	(19)
Allowance for equity funds used during construction	(26)	(19)	(19)
Other	19	22	13
Changes in assets and liabilities:
Receivables	(60)	(8)	75
Inventories	(32)	(11)	(13)
Accounts and wages payable	28	26	16
Taxes accrued	(27)	9	(15)
Regulatory assets and liabilities	(207)	(166)	17
Assets, other	(27)	(2)	(28)
Liabilities, other	(29)	(80)	(32)
Pension and other postretirement benefits	(2)	(3)	(5)
Net cash provided by operating activities	929	911	1,067
Cash Flows From Investing Activities:
Capital expenditures	(1,490)	(1,102)	(1,076)
Wind generation expenditures	(525)	(564)	0
Nuclear fuel expenditures	(44)	(66)	(31)
Purchases of securities – nuclear decommissioning trust fund	(452)	(224)	(256)
Proceeds from sales and maturities	439	183	260
Purchase of bonds	0	0	(207)
Proceeds from sale of remarketed bonds	0	0	207
Money pool advances, net	139
Money pool advances, net		(139)	0
Other	11	8	8
Net cash used in investing activities	(1,922)	(1,904)	(1,095)
Cash Flows From Financing Activities:
Dividends on common stock	(24)	(66)	(430)
Dividends on preferred stock	(3)	(3)	(3)
Short-term debt, net	165	(234)	179
Maturities of long-term debt	(8)	(92)	(580)
Issuances of long-term debt	524	1,012	778
Debt issuance costs	(5)	(9)	(9)
Capital contribution from parent	207	491	124
Net cash provided by financing activities	856	1,099	59
Net change in cash, cash equivalents, and restricted cash	(137)	106	31
Cash, cash equivalents, and restricted cash at beginning of year	145	39	8
Cash, cash equivalents, and restricted cash at end of year	8	145	39
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	205	190	190
Income taxes, net	19	25	101
Ameren Illinois Company
Cash Flows From Operating Activities:
Net income	427	382	346
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	471	434	405
Amortization of debt issuance costs and premium/discounts	13	12	12
Deferred income taxes and investment tax credits, net	165	118	80
Allowance for equity funds used during construction	(17)	(13)	(9)
Other	10	21	16
Changes in assets and liabilities:
Receivables	(17)	(28)	11
Inventories	(40)	(15)	2
Accounts and wages payable	2	15	(19)
Taxes accrued	22	(23)	21
Regulatory assets and liabilities	(222)	(72)	155
Assets, other	(75)	(76)	(23)
Liabilities, other	(45)	(46)	(5)
Pension and other postretirement benefits	(32)	(30)	(30)
Net cash provided by operating activities	662	679	962
Cash Flows From Investing Activities:
Capital expenditures	(1,432)	(1,447)	(1,208)
Other	(5)	3	3
Net cash used in investing activities	(1,437)	(1,444)	(1,205)
Cash Flows From Financing Activities:
Dividends on common stock	0	(9)	0
Dividends on preferred stock	(2)	(3)	(3)
Short-term debt, net	103	(53)	(19)
Money pool borrowings, net	(19)	19	0
Issuances of long-term debt	449	373	299
Redemption of preferred stock	(13)	0	0
Debt issuance costs	(6)	(4)	(4)
Capital contribution from parent	262	464	15
Other	(13)	0	0
Net cash provided by financing activities	761	787	288
Net change in cash, cash equivalents, and restricted cash	(14)	22	45
Cash, cash equivalents, and restricted cash at beginning of year	147	125	80
Cash, cash equivalents, and restricted cash at end of year	133	147	125
Cash Paid (Refunded) During the Year:
Interest (net of amounts capitalized, respectively)	148	137	127
Income taxes, net	$ (41)	$ 41	$ 4

Consolidated Statement Of Cas_2

Consolidated Statement Of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Interest Paid, Capitalized, Investing Activities	$ 17	$ 16	$ 20
Union Electric Company
Interest Paid, Capitalized, Investing Activities	10	10	12
Ameren Illinois Company
Interest Paid, Capitalized, Investing Activities	$ 7	$ 6	$ 8

Consolidated Statement Of Stock

Consolidated Statement Of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Other Paid-In Capital	Retained Earnings	Deferred Retirement Benefit Costs	Accumulated Other Comprehensive Income (Loss)	Total Ameren Corporation Stockholders' Equity	Noncontrolling Interest	Union Electric Company	Union Electric CompanyCommon Stock	Union Electric CompanyOther Paid-In Capital	Union Electric CompanyPreferred Stock Not Subject To Mandatory Redemption	Union Electric CompanyRetained Earnings	Ameren Illinois Company	Ameren Illinois CompanyCommon Stock	Ameren Illinois CompanyOther Paid-In Capital	Ameren Illinois CompanyPreferred Stock Not Subject To Mandatory Redemption	Ameren Illinois CompanyRetained Earnings
Beginning of year at Dec. 31, 2018		$ 2	$ 5,627	$ 2,024	$ (22)			$ 142			$ 1,903		$ 1,735			$ 2,173	$ 62	$ 1,539
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Settlement of forward sale agreement through common shares issuance		0	0
Stock Issued During Period, Value, New Issues			0
Shares issued under the DRPlus and 401(k) plan			68
Stock-based compensation activity			(1)
Capital contribution from parent									$ 124		124			$ 15		15
Net income	$ 834								429				429	346				346
Net Income (Loss) Available to Common Stockholders, Basic	828			828
Common stock dividends				(472)									(430)					0
Preferred stock dividends													(3)					(3)
Change in deferred retirement benefit costs	5				5
Net income attributable to noncontrolling interest holders	$ (6)							6
Dividends paid to noncontrolling interest holders								(6)
Redemptions of preferred stock								0									0
Beginning of year (shares) at Dec. 31, 2018	244,500,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under forward sale agreement	0
Stock Issued During Period, Shares, New Issues	0
Shares issued under the DRPlus and 401(k) plan	900,000
Stock Issued During Period, Shares, Other	800,000
End of year (shares) at Dec. 31, 2019	246,200,000
End of year at Dec. 31, 2019	$ 8,201	2	5,694	2,380	(17)	$ (17)		142		$ 511	2,027	$ 80	1,731		$ 0	2,188	62	1,882
Stockholders' equity, end of year at Dec. 31, 2019							$ 8,059		4,349					4,132
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 1.92
Settlement of forward sale agreement through common shares issuance		1	424
Stock Issued During Period, Value, New Issues			0
Shares issued under the DRPlus and 401(k) plan			51
Stock-based compensation activity			10
Capital contribution from parent									491		491			464		464
Net income	$ 877								$ 439				439	$ 382				382
Net Income (Loss) Available to Common Stockholders, Basic	871			871
Common stock dividends				(494)									(66)					(9)
Preferred stock dividends													(3)					(3)
Change in deferred retirement benefit costs	16				16
Net income attributable to noncontrolling interest holders	$ (6)							6
Dividends paid to noncontrolling interest holders								(6)
Redemptions of preferred stock								0									0
Shares issued under forward sale agreement	5,900,000
Stock Issued During Period, Shares, New Issues	0
Shares issued under the DRPlus and 401(k) plan	700,000
Stock Issued During Period, Shares, Other	500,000
End of year (shares) at Dec. 31, 2020	253,300,000								102,100,000					25,500,000
End of year at Dec. 31, 2020	$ 9,080	3	6,179	2,757	(1)	(1)		142		511	2,518	80	2,101		0	2,652	62	2,252
Stockholders' equity, end of year at Dec. 31, 2020	$ 8,938						8,938		$ 5,210					$ 4,966
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 2
Settlement of forward sale agreement through common shares issuance		0	113
Stock Issued During Period, Value, New Issues			148
Shares issued under the DRPlus and 401(k) plan			47
Stock-based compensation activity			15
Capital contribution from parent									207		207			262		262
Net income	$ 995								$ 521				521	$ 427				427
Net Income (Loss) Available to Common Stockholders, Basic	990			990
Common stock dividends				(565)									(24)					0
Preferred stock dividends													(3)					(2)
Change in deferred retirement benefit costs	14				14
Net income attributable to noncontrolling interest holders	$ (5)							5
Dividends paid to noncontrolling interest holders								(5)
Redemptions of preferred stock								(13)									(13)
Shares issued under forward sale agreement	1,600,000
Stock Issued During Period, Shares, New Issues	1,800,000
Shares issued under the DRPlus and 401(k) plan	500,000
Stock Issued During Period, Shares, Other	500,000
End of year (shares) at Dec. 31, 2021	257,700,000								102,100,000					25,500,000
End of year at Dec. 31, 2021	$ 9,829	$ 3	$ 6,502	$ 3,182	$ 13	$ 13		$ 129		$ 511	$ 2,725	$ 80	$ 2,595		$ 0	$ 2,914	$ 49	$ 2,677
Stockholders' equity, end of year at Dec. 31, 2021	$ 9,700						$ 9,700		$ 5,911					$ 5,640
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Cash Paid	$ 2.20

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES General Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has other subsidiaries that conduct other activities, such as providing shared services. • Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri, which includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers. • Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to a 43,700 square mile area in central and southern Illinois. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers. • Ameren Transmission Company of Illinois, doing business as ATXI, operates a FERC rate-regulated electric transmission business in the MISO. ATXI was incorporated in Illinois in 2006. In December 2020, ATXI completed construction of the ninth and final line segment of the Illinois Rivers transmission line, a MISO-approved electric transmission line. ATXI also operates the Spoon River and Mark Twain transmission lines, which were placed in service in February 2018 and December 2019, respectively. The COVID-19 pandemic continues to affect our results of operations, financial position, and liquidity. While our electric sales volumes, excluding the estimated effects of weather and customer energy-efficiency programs, increased in 2021, compared to 2020, and total sales volume levels were more comparable to pre-pandemic levels, there has been a shift in sales volumes by customer class, with an increase in residential sales, and a decrease in commercial and industrial sales. The continued effect of the COVID-19 pandemic on our results of operations, financial position, and liquidity in subsequent periods will depend on its severity and longevity, future regulatory or legislative actions with respect thereto, and the resulting impact on business, economic, and capital market conditions. We continue to assess the impacts the COVID-19 pandemic is having on our businesses, including but not limited to impacts on our liquidity; demand for residential, commercial, and industrial electric and natural gas services; changes in deferred payment arrangements for customers; bad debt expense; supply chain operations; the availability of our employees and contractors; counterparty credit; capital construction; infrastructure operations and maintenance; and pension valuations. While the revenues from Ameren Illinois’ electric distribution business, residential and small nonresidential customers of Ameren Illinois’ natural gas distribution business, and Ameren Illinois’ and ATXI’s electric transmission businesses are decoupled from changes in sales volumes, earnings at Ameren Missouri and those associated with Ameren Illinois’ large nonresidential natural gas customers are exposed to such changes. Regarding uncollectible accounts receivable, Ameren Illinois’ electric distribution and natural gas distribution businesses have bad debt riders, which provide for recovery of bad debt write-offs, net of any subsequent recoveries. Ameren Missouri does not have a bad debt rider or tracker, and thus its earnings are exposed to increases in bad debt expense, absent regulatory relief. However, Ameren Missouri has not experienced and does not expect a material impact to earnings from increases in bad debt expense. Our customers’ payment for our services has been impacted by the COVID-19 pandemic, resulting in a decrease to cash from operations. For information regarding Ameren Illinois’ suspension and subsequent reinstatement of customer disconnections and late fee charges for nonpayment and Ameren Missouri’s accounting authority orders related to the COVID-19 pandemic, see Note 2 – Rate and Regulatory Matters below. Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated, except as disclosed in Note 13 – Related-party Transactions. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. Regulation Our customer rates are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be refunded to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. See Note 2 – Rate and Regulatory Matters for additional information on our regulatory frameworks, regulatory recovery mechanisms, and regulatory assets and liabilities recorded at December 31, 2021 and 2020. We continually assess the recoverability of our respective regulatory assets. Regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that reductions in customers’ rates or refunds to customers related to regulatory liabilities are no longer probable, the amounts are credited to earnings. Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents include short-term, highly liquid investments purchased with an original maturity of three months or less. Cash and cash equivalents subject to legal or contractual restrictions and not readily available for use for general corporate purposes are classified as restricted cash. See Note 15 – Supplemental Information for a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows. Allowance for Doubtful Accounts Receivable The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has bad debt riders that adjust rates for net write-offs of customer accounts receivable above or below those being collected in rates. In 2020, the rider for electric distribution allowed for recovery of bad debt expense recognized under GAAP. Inventories Inventories are recorded at the lower of weighted-average cost or net realizable value. Inventories are capitalized when purchased and then expensed as consumed or capitalized as property, plant, and equipment when installed, as appropriate. See Note 15 – Supplemental Information for the components of inventories. Property, Plant, and Equipment, Net We capitalize the cost of additions to, and betterments of, units of property, plant, and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures are expensed as incurred. Beginning in 2020, maintenance expenses related to scheduled Callaway nuclear refueling and maintenance outages, which were previously expensed as incurred, are deferred and amortized over the number of expected months until the completion of the next refueling outage, which historically has been approximately 18 months . When units of depreciable property are retired, the original costs, and the associated removal cost, net of salvage, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations section below and Note 3 – Property, Plant, and Equipment, Net for additional information. Ameren Missouri’s cost of nuclear fuel is capitalized as a part of “Property, Plant, and Equipment, Net” on the balance sheet and then amortized to “Operating Expenses – Fuel” in the statement of income on a unit-of-production basis. Plant to be Abandoned, Net When it becomes probable an asset will be retired significantly in advance of its previously expected useful life and in the near term, the Ameren Companies must assess the probability of full recovery of the remaining net book value of the asset to be abandoned. We recognize a loss on abandonment when it becomes probable that all or part of the cost of an asset, including a return at the applicable WACC, will be disallowed from recovery either through customer rates or through the issuance of securitized utility tariff bonds and such amount is reasonably estimable. An abandonment loss, if any, would equal the difference between the remaining net book value of the asset and the present value of the expected future cash flows. If the asset is still in service, the net book value is classified as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on the balance sheet. The net book value will be classified as a regulatory asset on the balance sheet when the asset is no longer in service or as required by a rate order. In relation to the NSR and Clean Air Act litigation discussed in Note 14 – Commitments and Contingencies, in December 2021, Ameren Missouri filed a motion with the United States District Court for the Eastern District of Missouri to modify a previously issued remedy order to allow the retirement of the Rush Island Energy Center in lieu of installing a flue gas desulfurization system. As of December 31, 2021, Ameren and Ameren Missouri determined that the Rush Island Energy Center met the criteria to be considered probable of abandonment and have classified its remaining net book value as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on Ameren’s and Ameren Missouri’s balance sheets. See Note 3 – Property, Plant, and Equipment, Net for our plant to be abandoned balance as of December 31, 2021. Ameren Missouri is currently allowed a full recovery of and a full return on its investment in Rush Island Energy Center and has concluded that no abandonment loss was required as of December 31, 2021. As part of the assessment of any potential future abandonment loss, consideration will be given to rate and securitization orders issued by the MoPSC to Ameren Missouri and to orders issued to other Missouri utilities with similar facts. Depreciation Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The composite rates include a provision for the estimated removal cost of property, plant, and equipment retired from service, net of salvage. The provision for depreciation for the Ameren Companies in 2021, 2020, and 2019 ranged from 3% to 4% of the average depreciable cost. See Note 3 – Property, Plant, and Equipment, Net for additional information on estimated depreciable lives. Allowance for Funds Used During Construction As a part of “Property, Plant, and Equipment, Net” on the balance sheet, we capitalize allowance for funds used during construction, which is the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to eligible rate-regulated construction work in progress, in accordance with the utility industry’s accounting practice and GAAP. The amount of allowance for funds used during construction is calculated using a FERC-prescribed formula based on a rate, which incorporates the average cost of short-term debt, the average cost of long-term debt, and the cost of equity funds. The portion attributable to borrowed funds is recorded as a reduction of “Interest Charges” on the statements of income. The portion attributable to equity funds is recorded within “Other Income, Net” on the statements of income. This accounting practice offsets the effect on earnings of the cost of financing during construction. See Note 15 – Supplemental Information for the amount of allowance for funds used during construction capitalized and the average rate applied to eligible construction work in progress. Allowance for funds used during construction does not represent a current source of cash funds. Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates. Goodwill Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had goodwill of $411 million at December 31, 2021 and 2020. Ameren has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2021 and 2020. The Ameren Transmission reporting unit had the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit at December 31, 2021 and 2020. Ameren and Ameren Illinois evaluate goodwill for impairment in each of their reporting units as of October 31 each year, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of their reporting units below their carrying amounts. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a quantitative test. Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2021. As part of this qualitative assessment, Ameren and Ameren Illinois evaluated, among other things, macroeconomic conditions, industry and market considerations such as observable industry market multiples, regulatory frameworks, cost factors, overall financial performance, and entity-specific events. The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was more likely than not that the fair value of each reporting unit exceeded its carrying value as of October 31, 2021, resulting in no impairment of Ameren’s or Ameren Illinois’ goodwill. Impairment of Long-lived Assets We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine that an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of long-lived assets may not be recoverable in 2021, 2020 or 2019. Variable Interest Entities As of December 31, 2021 and 2020, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $56 million and $37 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of December 31, 2021, the maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $56 million plus associated outstanding funding commitments of $28 million . Environmental Costs Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates. See Note 14 – Commitments and Contingencies for additional information on liabilities for environmental costs. Asset Retirement Obligations and Removal Costs We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs for accretion and changes in the estimated fair values of the obligations, with a corresponding increase or decrease in the asset book value for the fair value changes. Asset book values, reflected within “Property, Plant, and Equipment, Net” on the balance sheet, are depreciated over the remaining useful life of the related asset. Due to regulatory recovery, that depreciation is deferred as a regulatory balance. The depreciation of the asset book values at Ameren Missouri was $14 million , $28 million, and $18 million for the years ended December 31, 2021, 2020, and 2019, respectively, which was deferred as a reduction to the net regulatory liability. The net regulatory liability also reflects a deferral for the nuclear decommissioning trust fund balance for the Callaway Energy Center. The depreciation deferred to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with decommissioning of Ameren Missouri’s Callaway and wind renewable energy centers, certain Ameren Missouri solar energy centers, CCR facilities, and river structures at certain energy centers used for unloading coal and circulating water systems. Additionally, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. See Note 15 – Supplemental Information for a reconciliation of the beginning and ending carrying amounts of AROs. Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment retired from service, net of salvage, represent a cost of removal regulatory liability. See the cost of removal regulatory liability balance in Note 2 – Rate and Regulatory Matters. Company-owned Life Insurance Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of December 31, 2021, the cash surrender value of company-owned life insurance at Ameren and Ameren Illinois was $278 million (December 31, 2020 – $272 million) and $117 million (December 31, 2020 – $115 million), respectively, while total borrowings against the policies were $109 million (December 31, 2020 – $107 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance sheets. The net cash surrender value of Ameren’s company-owned life insurance is affected by the investment performance of a separate account in which Ameren holds a beneficial interest. Operating Revenues We record revenues from contracts with customers for various electric and natural gas services, which primarily consist of retail distribution, electric transmission, and off-system arrangements. When more than one performance obligation exists in a contract, the consideration under the contract is allocated to the performance obligations based on the relative standalone selling price. Electric and natural gas retail distribution revenues are earned when the commodity is delivered to our customers. We accrue an estimate of electric and natural gas retail distribution revenues for service provided but unbilled at the end of each accounting period. Electric transmission revenues are earned as electric transmission services are provided. Off-system revenues are primarily comprised of MISO revenues and wholesale bilateral revenues. MISO revenues include the sale of electricity, capacity, and ancillary services. Wholesale bilateral revenues include the sale of electricity and capacity. MISO-related electricity and wholesale bilateral electricity revenues are earned as electricity is delivered. Capacity and ancillary service revenues are earned as services are provided. Retail distribution, electric transmission, and off-system revenues, including the underlying components described above, represent a series of goods or services that are substantially the same and have the same pattern of transfer over time to our customers. Revenues from contracts with customers are equal to the amounts billed and our estimate of electric and natural gas retail distribution services provided but unbilled at the end of each accounting period. Customers are billed at least monthly, and payments are due less than one month after goods and/or services are provided. See Note 16 – Segment Information for disaggregated revenue information. For certain regulatory recovery mechanisms that are alternative revenue programs rather than revenues from contracts with customers, we recognize revenues that have been authorized for rate recovery, are objectively determinable and probable of recovery, and are expected to be collected from customers within two years from the end of the year. Our alternative revenue programs include revenue requirement reconciliations, the MEEIA, the VBA, and the WNAR. These revenues are subsequently recognized as revenues from contracts with customers when billed, with an offset to alternative revenue program revenues. As of December 31, 2021 and 2020, our remaining performance obligations were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. Accounting for MISO Transactions MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by the MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri’s and Ameren Illinois’ prior-period transactions will be resettled outside the routine settlement process because of a change in the MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize revenues and expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. There were no material MISO resettlements in 2021, 2020, or 2019. Stock-based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite vesting period. To the extent that actual forfeitures differ from estimated forfeitures, such differences are accounted for as a cumulative adjustment to compensation expense and recorded in the period that estimates are revised. Compensation cost is ultimately recognized only for awards for which the requisite service was provided. See Note 11 – Stock-based Compensation for additional information. Unamortized Debt Discounts, Premiums, and Issuance Costs Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of the agreement. Income Taxes Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates. We expect that regulators will reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in certain deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases. To the extent deferred tax balances are included in rate base, the revaluation of deferred taxes is recorded as a regulatory asset or liability on the balance sheet and will be collected from, or refunded to, customers. For deferred tax balances not included in rate base, the revaluation of deferred taxes is recorded as an adjustment to income tax expense on the income statement. See Note 12 – Income Taxes for further information regarding the revaluation of deferred taxes related to Missouri state corporate income tax rate changes. Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax using a stand-alone calculation, which is similar to what would be owed or refunded had the party been separately subject to tax without considering the impact of consolidation. Any net benefit attributable to Ameren (parent) is reallocated to the other parties. This reallocation is treated as a capital contribution to the party receiving the benefit. See Note 13 – Related-party Transactions for information regarding capital contributions under the tax allocation agreement.

Rate And Regulatory Matters

Rate And Regulatory Matters	12 Months Ended
	Dec. 31, 2021
Public Utilities, General Disclosures [Abstract]
Public Utilities Disclosure [Text Block]	RATE AND REGULATORY MATTERS Below is a summary of our regulatory frameworks and significant regulatory proceedings and related lawsuits. We are unable to predict the ultimate outcome of these matters, the timing of final decisions of the various agencies and courts, or the effect on our results of operations, financial position, or liquidity. Regulatory Frameworks The following table presents the regulatory frameworks and significant regulatory recovery mechanisms for each of Ameren’s rate-regulated businesses, which are discussed in more detail below: Ameren Missouri Ameren Illinois’ electric distribution business Ameren Illinois’ natural gas delivery service business Ameren Illinois’ and ATXI’s electric transmission business Regulatory framework • Historical test year ratemaking • Natural gas revenues for residential customers adjusted for sales volume deviations resulting from weather through the WNAR • Performance-based formula ratemaking • Initial rates based on historical test year and expected net plant additions for the year before rates become effective • Revenues decoupled from sales volumes • Future test year ratemaking • Revenues for residential and small nonresidential customers decoupled from sales volumes through the VBA • Formula ratemaking • Initial rates based on future test year • Revenues decoupled from sales volumes Regulatory mechanisms • PISA Riders: • RESRAM • FAC • MEEIA • PGA • WNAR Trackers: • Pension and postretirement benefit costs • Certain excess deferred income taxes • Renewable energy standard costs • Electric distribution service and energy-efficiency revenue requirement reconciliation adjustments Riders: • Power procurement • Transmission services • Renewable energy credit compliance • Zero emission credits • Certain environmental costs • Bad debt write-offs • Costs of certain asbestos-related claims Riders: • QIP • PGA • VBA • Energy-efficiency program costs • Certain environmental costs • Bad debt write-offs • Invested capital taxes • Revenue requirement reconciliation adjustment Missouri The MoPSC regulates rates and other matters for Ameren Missouri’s electric service and natural gas distribution businesses. The rates Ameren Missouri charges customers for these services are established in a traditional regulatory rate review, which takes up to 11 months to complete, based on a historical test year and the revenue requirement established in the review. Ameren Missouri has recovery mechanisms, including the RESRAM, FAC, MEEIA, PGA, and WNAR, that allow customer rates to be adjusted without a traditional regulatory rate review. These riders, along with the PISA, each described in more detail below, partially mitigate the effects of regulatory lag. Ameren Missouri also employs other recovery mechanisms, including a pension and postretirement benefit cost tracker, an uncertain income tax position tracker, a tracker on certain excess deferred income taxes, and a renewable energy standard cost tracker. Each of these trackers allows Ameren Missouri to defer the difference between actual costs incurred and costs included in customer rates as a regulatory asset or regulatory liability, with the difference expected to be reflected in base rates in a subsequent MoPSC rate order. Ameren Missouri’s cost recovery under any of its recovery mechanisms is subject to MoPSC prudence reviews. The PISA permits Ameren Missouri to defer and recover 85% of the depreciation expense and earn a return at the applicable WACC on investments in certain property, plant, and equipment placed in service, and not included in base rates. The regulatory asset for accumulated PISA deferrals also earns a return at the applicable WACC, with all approved PISA deferrals added to rate base prospectively and recovered over a period of 20 years following a regulatory rate review. Additionally, under the RESRAM, Ameren Missouri is permitted to recover the 15% of depreciation expense not recovered under the PISA, and earn a return at the applicable WACC for investments in renewable generation plant placed in service to comply with Missouri’s renewable energy standard. The RESRAM deferrals are a regulatory asset until they are included in customer rates and collected in a subsequent period. Those investments not eligible for recovery under the PISA and the remaining 15% of certain property, plant, and equipment placed in service, unless eligible for recovery under the RESRAM, remain subject to regulatory lag. Ameren Missouri defers its cost of debt relating to PISA eligible investments as an offset to interest charges with the difference between the applicable WACC and its cost of debt recognized in revenues when recovery of such deferrals is reflected in customer rates. Under Missouri law, as a result of the PISA election, additional provisions apply to Ameren Missouri. These provisions include limiting Ameren Missouri’s rate increases to a 2.85% compound annual growth rate in the average overall customer rate per kilowatthour, based on the electric rates that became effective in April 2017, less half of the annual savings from the TCJA that was passed on to customers as approved in a July 2018 MoPSC order. If rate changes from the FAC or the RESRAM riders would cause rates to temporarily exceed the 2.85% rate cap, the overage would be deferred for future recovery in the next regulatory rate review; however, rates established in such regulatory rate review would be subject to the rate cap. Any deferred overages approved for recovery would be recovered in a manner consistent with costs recovered under the PISA. Excluding customer rates under the MEEIA rider, which are not subject to the rate cap, Ameren Missouri would incur a penalty equal to the amount of deferred overage that would cause customer rates to exceed the 2.85% rate cap. Ameren Missouri did not incur a penalty related to the rate cap in 2021. Both the rate increase limitation and the PISA are effective through December 2023. Missouri law provides for the ability to use the PISA, if Ameren Missouri requests and receives MoPSC approval for extension, through December 2028. The RESRAM permits Ameren Missouri to recover or refund, through customer rates, the difference between the cost of compliance, net of renewable tax credits, with Missouri’s renewable energy standard and the amount set in base rates. Effective February 28, 2022, all off-system sales from the High Prairie Renewable and Atchison Renewable energy centers will be included in the RESRAM. Previously, 95% of these sales were included in the FAC and 5% were included in the RESRAM. Customer rates are adjusted for the RESRAM on an annual basis without a traditional regulatory rate review, subject to MoPSC prudence reviews. The difference between actual compliance costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period. RESRAM regulatory assets earn carrying costs at short-term interest rates. The RESRAM permits Ameren Missouri to recover investments in wind generation and other renewables related to compliance with Missouri’s renewable energy standard, and earn a return at the applicable WACC on those investments not already provided for in customer rates or any other recovery mechanism, such as the renewable energy standard cost tracker. The renewable energy standard cost tracker allows Ameren Missouri to defer differences between actual costs primarily associated with the Maryland Heights Energy Center and renewable energy credits obtained through a 102-MW power purchase agreement with a wind farm operator, which expires in 2024, and those costs included in customer rates. The FAC permits Ameren Missouri to recover or refund, through customer rates, 95% of the variance in net energy costs from the amount set in base rates without a traditional regulatory rate review, subject to MoPSC prudence reviews, with the remaining 5% of changes retained by Ameren Missouri. As such, Ameren Missouri’s results of operations are affected by the 5% not recovered or refunded under the FAC. The 95% variance in net energy costs in a given period is deferred as a regulatory asset or liability, and either billed or refunded to customers in a subsequent period. FAC regulatory assets earn carrying costs at short-term interest rates. Ameren Missouri’s base rates for electric service are required to be reset at least every four years to allow for continued use of the FAC. The MEEIA permits Ameren Missouri to recover customer energy-efficiency program costs, the related lost electric margins, and any performance incentive through the MEEIA without a traditional regulatory rate review, subject to MoPSC prudence reviews. MEEIA assets earn carrying costs at short-term interest rates. Ameren Missouri is a member of the MISO, and its transmission rate is calculated in accordance with the MISO Open Access Transmission, Energy, and Operating Reserve Markets Tariff. The FERC regulates the rates charged and the terms and conditions for wholesale electric transmission service. The transmission rate update each June is based on Ameren Missouri’s actual historical cost from the prior calendar year. This rate is not directly charged to Missouri retail customers because, in Missouri, the revenue requirement used to set bundled retail base rates includes an amount for transmission-related costs and revenues. The PGA allows Ameren Missouri to recover costs of natural gas purchased on behalf of its customers without a traditional regulatory rate review, subject to MoPSC prudence reviews. These pass-through purchased gas costs do not affect Ameren Missouri’s natural gas margins, as any change in costs is offset by a corresponding change in revenues. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period. PGA regulatory assets earn carrying costs at short-term interest rates. The WNAR will allow Ameren Missouri to adjust natural gas delivery service rates charged to residential customers without a traditional regulatory rate review, subject to MoPSC prudence reviews, when deviations from normal weather conditions cause natural gas revenues to vary from the related revenue requirement approved by the MoPSC in the previous regulatory rate review. The impact of deviations from normal weather on natural gas delivery service revenues billed to residential customers in a given period will be deferred as a regulatory asset or liability. WNAR regulatory assets will earn carrying costs at short-term interest rates. The deferred amount will either be billed or refunded to residential customers in a subsequent period. The WNAR was approved by the December 2021 MoPSC natural gas rate order discussed below, and will replace the DCA effective February 28, 2022. Illinois The ICC regulates rates and other matters for Ameren Illinois’ electric distribution service and natural gas distribution businesses. The rates Ameren Illinois charges customers for electric distribution service are calculated under a performance-based formula ratemaking framework pursuant to the IEIMA. Pursuant to the IETL and an order issued by the ICC in March 2021, Ameren Illinois expects to use the current IEIMA formula framework to establish annual customer rates effective through 2023 and reconcile the related revenue requirements, and anticipates filing an MYRP by mid-January 2023, with rates effective beginning in 2024. By law, the decoupling provisions extend beyond the end of existing performance-based formula ratemaking, which ensures that Ameren Illinois’ electric distribution revenues authorized in a regulatory rate review are not affected by changes in sales volumes. See below for additional information regarding the IETL, the MYRP, and the March 2021 ICC order. The rates Ameren Illinois charges customers for natural gas distribution service are established in a traditional regulatory rate review, which takes up to 11 months to complete, based on a future test year and the revenue requirement established in the review. Ameren Illinois’ election to use the electric distribution service performance-based formula ratemaking framework allowed by state law, described below, permits Ameren Illinois to adjust customer rates to recover the cost of electric distribution service on an annual basis. Ameren Illinois’ electric distribution service also has other cost recovery mechanisms in place that allow customer rates to be adjusted without a traditional regulatory rate review. Ameren Illinois’ electric distribution service business has riders for power procurement and transmission services incurred on behalf of its customers, renewable energy credit compliance, zero emission credits, and certain environmental costs, as well as bad debt write-offs and the costs of certain asbestos-related claims not recovered in base rates. These pass-through costs do not affect Ameren Illinois’ net income, as any change in costs is offset by a corresponding change in revenues. Ameren Illinois’ cost recovery under any of its recovery mechanisms is subject to ICC prudence reviews. Ameren Illinois’ electric distribution service performance-based formula ratemaking framework under the IEIMA allows Ameren Illinois to reconcile electric distribution service rates to its actual revenue requirement on an annual basis. If a given year’s revenue requirement varies from the amount collected from customers, an adjustment is made to electric operating revenues with an offset to a regulatory asset or liability to reflect that year’s actual revenue requirement, independent of actual sales volumes. The regulatory balance is then collected from, or refunded to, customers within two years from the end of the year. In addition, Ameren Illinois’ electric customer energy-efficiency rider provides Ameren Illinois’ electric distribution service business with recovery of, and return on, energy-efficiency investments. Under formula ratemaking for both its electric distribution service and its electric energy-efficiency investments, the revenue requirements are based on recoverable costs, year-end rate base, and a year-end ratemaking capital structure, and earn a return at the applicable WACC. The ROE component of the applicable WACC is based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points and any performance-related basis point adjustments, described in more detail below. Therefore, Ameren Illinois’ annual ROE for its electric distribution business is directly correlated to the yields on such bonds. In addition, regulatory assets applicable to formula ratemaking for both electric distribution service and electric energy-efficiency investments earn a return at the applicable WACC. However, Ameren Illinois recognizes the cost of debt on these regulatory assets in revenue, instead of the applicable WACC, with the difference recognized in revenues when recovery of such regulatory assets is reflected in customer rates. Ameren Illinois’ electric distribution service business is also subject to performance standards. Failure to achieve the standards would result in a reduction in the company’s allowed ROE calculated under the formula ratemaking recovery mechanism. The performance standards applicable to electric distribution service under the IEIMA include improvements in service reliability to reduce both the frequency and duration of outages, a reduction in the number of estimated bills, a reduction of consumption from inactive meters, and a reduction in bad debt expense. The allowed ROE for electric distribution service may be decreased for penalties up to 38 basis points in 2022 and up to 10 basis points in 2023 if these performance standards are not met. The allowed ROE on energy-efficiency investments can be increased or decreased up to 200 basis points, depending on the achievement of annual energy savings goals. Any adjustments to the allowed ROE for energy-efficiency investments will depend on annual performance for a historical period relative to energy savings goals. In 2021, 2020, and 2019, there were no performance-related basis point adjustments that materially affected financial results. Ameren Illinois’ natural gas distribution business has recovery mechanisms, including the QIP, PGA, and VBA, that allow customer rates to be adjusted without a traditional regulatory rate review. These riders, described in more detail below, mitigate the effects of regulatory lag. Ameren Illinois employs other riders for natural gas customer energy-efficiency program costs and certain environmental costs, as well as bad debt write-offs and invested capital taxes not recovered in base rates. Pass-through costs under the riders do not affect Ameren Illinois’ net income, as any change in costs is offset by a corresponding change in revenues. Ameren Illinois’ cost recovery under any of its recovery mechanisms is subject to ICC prudence reviews. The QIP provides Ameren Illinois with recovery of, and a return on, qualifying natural gas infrastructure investments that are placed in service between regulatory rate reviews. Infrastructure investments under the QIP earn a return at the applicable WACC. Eligible natural gas investments include projects to improve safety and reliability and modernization investments, such as smart meters. The deferrals are recorded as a regulatory asset, with recovery beginning two months after the qualifying natural gas plant is placed in service and continuing until such plant is included in base rates in a natural gas delivery service rate order. Ameren Illinois’ QIP is subject to a rate impact limitation of a cumulative 4% per year since the most recent delivery service rate order, with no single year exceeding 5.5%. If the rate impact limitation was met in a particular year, the amount of rate base causing the QIP rate to exceed the limitation would be exposed to regulatory lag until a year when that amount could be recovered under QIP or is added to rate base as a part of a regulatory rate review. Upon issuance of a natural gas delivery service rate order, QIP rate base is transferred to base rates and the QIP is reset to zero, which mitigates the risk that the QIP will exceed its statutory limitations in future years and ensures timely recovery of capital investments. Without legislative action, the QIP will expire after December 2023. The PGA allows Ameren Illinois to recover costs of natural gas purchased on behalf of its customers without a traditional regulatory rate review, subject to ICC prudence reviews. These pass-through purchased gas costs do not affect Ameren Illinois natural gas margins, as any change in costs is offset by a corresponding change in revenues. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period. PGA regulatory assets earn carrying costs at short-term interest rates. The VBA ensures recoverability of the natural gas distribution service revenue requirement that is dependent on sales volumes for residential and small nonresidential customers. For these rate classes, the VBA allows Ameren Illinois to adjust natural gas distribution service rates without a traditional regulatory rate review when changes occur in sales volumes from those volumes approved by the ICC in a previous regulatory rate review. The difference between allowed sales revenues and amounts billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is collected from, or refunded to, customers in a subsequent period. VBA regulatory assets for a given year that are not fully collected by the end of the following year begin earning carrying costs at short-term interest rates. Federal The FERC regulates rates and other matters for Ameren Illinois’ transmission business and ATXI, as well as for Ameren Missouri. See discussion above related to Ameren Missouri. Both Ameren Illinois and ATXI are members of the MISO, and their transmission rates are calculated in accordance with the MISO Open Access Transmission, Energy, and Operating Reserve Markets Tariff. Ameren Illinois and ATXI have received FERC approval to use a company-specific, forward-looking formula ratemaking framework in setting their transmission rates. These forward-looking rates are updated annually and become effective each January with forecasted information. The formula rate framework provides for an annual reconciliation of the electric transmission service revenue requirement, which reflects the actual recoverable costs incurred and the 13-month average rate base for a given year, with the revenue requirement in customer rates, including an allowed ROE. If a given year’s revenue requirement varies from the amount collected from customers, an adjustment is made to electric operating revenues with an offset to a regulatory asset or liability to reflect that year’s actual revenue requirement, independent of actual sales volumes. The regulatory balance is collected from, or refunded to, customers within two years from the end of the year. FERC revenue requirement reconciliation adjustment regulatory assets earn carrying costs at each company’s short-term interest rates. In addition, the FERC has approved transmission rate incentives, including a 50 basis point incentive adder to the allowed base ROE for Ameren Illinois and ATXI for participation in an RTO. Proceedings and Updates Missouri December 2021 MoPSC Electric Rate Order In December 2021, the MoPSC issued an order in Ameren Missouri’s 2021 electric service regulatory rate review, approving nonunanimous stipulations and agreements. The order will result in an increase of $220 million to Ameren Missouri’s annual revenue requirement for electric retail service. The approved revenue requirement is based on a rate base of $10.2 billion, infrastructure investments as of September 30, 2021, and a change in the depreciable lives of the Sioux and Rush Island energy centers’ assets consistent with Ameren Missouri’s 2020 IRP. The order did not specify an ROE, but specified that Ameren Missouri’s September 30, 2021 capital structure, which was composed of 51.97% common equity, will be used in the PISA and RESRAM. The order provides for the continued use of the FAC and trackers for pension and postretirement benefits, uncertain income tax positions, certain excess deferred income taxes, and renewable energy standard costs that the MoPSC previously authorized in earlier electric rate orders. The order also changed annualized depreciation, regulatory asset and liability amortization amounts, and the base level of expenses for trackers. On an annualized basis, these changes reflect approximate increases in depreciation and amortization of $140 million and other operating and maintenance expenses of $40 million. As a result of the order, all off-system sales resulting from the High Prairie Renewable and Atchison Renewable energy centers will be included in the RESRAM beginning February 28, 2022. Prior to this change, 95% of these sales were included in the FAC and 5% were included in the RESRAM. The order also establishes a five-year recovery period for $61 million of certain costs associated with the Meramec Energy Center, which is expected to be retired in 2022. The new rates, base level of expenses, and amortizations will become effective on February 28, 2022. MoPSC Staff Review of Planned Rush Island Energy Center Retirement In February 2022, the MoPSC issued an order directing the MoPSC staff to review Ameren Missouri’s planned accelerated retirement of the Rush Island Energy Center as a result of the NSR and Clean Air Act Litigation discussed in Note 14 – Commitments and Contingencies. The MoPSC staff’s review will include potential impacts on the reliability and cost of Ameren Missouri’s service to its customers, Ameren Missouri’s plans to mitigate the customer impacts of the accelerated retirement, and the prudence of Ameren Missouri’s actions and decisions with regard to the Rush Island Energy Center, among other things. The MoPSC staff is under no deadline to complete this review. Ameren Missouri is unable to predict the ultimate resolution of this matter; however, such resolution could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. December 2021 MoPSC Natural Gas Rate Order In December 2021, the MoPSC issued an order in Ameren Missouri’s 2021 natural gas delivery service regulatory rate review, approving nonunanimous stipulations and agreements. The order will result in an increase of $5 million to Ameren Missouri’s annual revenue requirement for natural gas delivery service. The approved revenue requirement is based on a rate base of $313 million and infrastructure investments as of September 30, 2021. The order did not specify an ROE or a capital structure. The order provides for the continued use of the PGA and trackers for pension and postretirement benefits and certain excess deferred income taxes that the MoPSC previously authorized in earlier natural gas rate orders. The order also authorizes the use of the WNAR, which replaces the DCA and is discussed above. The new rates will become effective on February 28, 2022. Accounting Authority Orders Related to COVID-19 Pandemic Costs In March 2021, the MoPSC issued orders approving nonunanimous stipulation and agreements related to Ameren Missouri’s electric and natural gas service accounting authority order requests. The orders allowed Ameren Missouri to accumulate $9 million of certain costs incurred related to the COVID-19 pandemic, net of cost savings, as well as forgone customer late fee and reconnection fee revenues from March 2020 to March 2021. The accumulated costs and forgone customer late fee and reconnection fee revenues were approved for recovery in the MoPSC’s December 2021 electric and natural gas rate orders discussed above. In March 2021, Ameren Missouri deferred other operations and maintenance expenses of $5 million as a regulatory asset related to the accounting authority orders and will amortize the balance over a five-year period once new rates become effective on February 28, 2022. Ameren Missouri will recognize the remaining $4 million associated with forgone customer late fee and reconnection fee revenue when billed to customers over the five-year period beginning on February 28, 2022. MEEIA In September 2021, the MoPSC issued an order approving Ameren Missouri’s energy savings results for the second year of the MEEIA 2019 program. As a result of this order and MoPSC orders issued in September 2017, October 2018, January 2019, September 2019, and August 2020, and in accordance with revenue recognition guidance, Ameren Missouri recognized revenues of $9 million, $6 million, and $37 million in 2021, 2020, and 2019 respectively. In October 2021, the MoPSC issued an order approving Ameren Missouri’s request to implement the 2023 program year of its MEEIA 2019 program. The order established performance incentives that would provide Ameren Missouri an opportunity to earn additional revenues, including $13 million if Ameren Missouri achieves certain energy-efficiency goals during the 2023 program year. Ameren Missouri intends to invest $75 million in energy-efficiency programs during the 2023 program year. Extension of PGA Recovery In October 2021, the MoPSC issued an order allowing Ameren Missouri to extend the collection period for the cumulative PGA under-recovery as of August 2021, which includes the February 2021 under-recovery of $53 million, from 12 months to 36 months beginning November 2021, to lessen the impact on customer rates. Similar to other deferrals under the PGA, the deferral associated with the February 2021 under-recovery earns carrying costs at short-term interest rates. Illinois IETL The IETL was enacted in September 2021. The IETL resulted in changes to the regulatory framework applicable to Ameren Illinois’ electric distribution business by giving Ameren Illinois the option to file an MYRP with the ICC by mid-January 2023, with rates effective beginning in 2024, among other things. Ameren Illinois has the option to file for an MYRP every four years. Subject to a constructive outcome regarding the ICC’s determination of performance metrics, Ameren Illinois anticipates filing an MYRP for rates effective beginning in 2024. If it does not file by mid-January 2023, its next opportunity to file an MYRP would be for rates effective beginning in 2028. Ameren Illinois expects to continue to use the current IEIMA performance-based formula ratemaking framework to establish annual customer rates effective through 2023 and reconcile the related revenue requirements. In order to utilize the IEIMA reconciliation, Ameren Illinois must file either a traditional regulatory rate review or an MYRP pursuant to the IETL by mid-January 2023. Under the MYRP, the ICC would approve base rates for electric distribution service to be charged to customers for each calendar year of a four-year period. The base rates for a particular calendar year would be based on forecasted recoverable costs and an ICC-determined ROE applied to Ameren Illinois’ forecasted average annual rate base using a forecasted capital structure, with a common equity ratio of up to 50% being deemed prudent and reasonable by law and a higher equity ratio requiring specific ICC approval. The ROE determined by the ICC is applicable to each calendar year of the four-year period. Under a traditional regulatory rate review, the revenue requirement may be based on a future test year and would include an ROE determined by the ICC. Ameren Illinois’ existing riders will remain effective whether it elects to file an MYRP or a traditional regulatory rate review. Additionally, electric distribution service revenues would continue to be decoupled from sales volumes under either election. The MYRP would also allow Ameren Illinois to reconcile electric distribution service rates to its actual revenue requirement on an annual basis, subject to a reconciliation cap, which provides that the actual revenue requirement does not exceed 105% of the annual revenue requirement approved by the ICC. Certain variations from forecasted costs would be excluded from the reconciliation cap, including those associated with major storms; new business and facility relocations; changes in the timing of expenditures or investments into or out of the applicable calendar year; and changes in interest rates, income taxes, taxes other than income taxes, pension and other post-retirement benefits costs, and amortization of certain regulatory assets. The reconciliation cap would also exclude costs recovered through riders outside of base rates, such as riders for electric energy-efficiency investments, power procurement and transmission services, renewable energy credit compliance, zero emission credits, certain environmental costs, and bad debt write-offs, among others. The actual revenue requirement for a particular year would incorporate Ameren Illinois’ year-end rate base and actual capital structure for such year, provided that the common equity ratio in such capital structure may not exceed that approved by the ICC in the MYRP. Additionally, the ICC-determined ROE in the MYRP would be subject to annual adjustments during the four-year period based on certain performance metrics relating to delivery system reliability, supplier diversity, affordability of customer delivery service cost, customer service performance, timeliness of response to customer requests for interconnection of distributed energy resources, and reductions in peak load due to demand response programs, with aggregate symmetrical performance-based ROE incentives and penalties ranging from 20 to 60 basis points annually. In January 2022, Ameren Illinois filed a request with the ICC proposing performance metrics that would be used in determining ROE incentives and penalties. The ICC is required to issue an order on this matter by September 30, 2022. Excluding potential phase-in of the initial rate increase discussed below, if a given year’s revenue amount collected from customers varies from the approved revenue requirement, an adjustment would be made to electric operating revenues with an offset to a reg

Property And Plant, Net

Property And Plant, Net	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
PROPERTY AND PLANT, NET	PROPERTY, PLANT, AND EQUIPMENT, NET The following table presents components of “Property, plant, and equipment, net” at December 31, 2021 and 2020: Ameren Ameren Other Ameren 2021 Property, plant, and equipment at original cost: (a) Electric generation: Coal (b)(c) $ 3,955 $ — $ — $ 3,955 Natural gas 1,105 — — 1,105 Nuclear 5,615 — — 5,615 Renewable (d) 1,889 — — 1,889 Electric distribution 7,286 7,017 — 14,303 Electric transmission 1,628 4,105 1,800 7,533 Natural gas 607 3,586 — 4,193 Other (e) 1,584 1,183 242 3,009 23,669 15,891 2,042 41,602 Less: Accumulated depreciation and amortization 9,784 4,100 330 14,214 13,885 11,791 1,712 27,388 Construction work in progress: Nuclear fuel in process 133 — — 133 Other 674 432 30 1,136 Plant to be abandoned, net (f) 604 — — 604 Property, plant, and equipment, net $ 15,296 $ 12,223 $ 1,742 $ 29,261 2020 Property, plant, and equipment at original cost: (a) Electric generation: Coal (b)(c) $ 4,875 $ — $ — $ 4,875 Natural gas 1,097 — — 1,097 Nuclear 5,608 — — 5,608 Renewable (d) 1,301 — — 1,301 Electric distribution 6,784 6,649 — 13,433 Electric transmission 1,482 3,575 1,774 6,831 Natural gas 561 3,308 — 3,869 Other (e) 1,390 1,070 245 2,705 23,098 14,602 2,019 39,719 Less: Accumulated depreciation and amortization 9,689 3,780 304 13,773 13,409 10,822 1,715 25,946 Construction work in progress: Nuclear fuel in process 75 — — 75 Other 395 379 12 786 Property, plant, and equipment, net $ 13,879 $ 11,201 $ 1,727 $ 26,807 (a) The estimated lives for each asset group are as follows: 5 to 72 years for electric generation, excluding Ameren Missouri’s hydroelectric generating assets, which have useful lives of up to 150 years; 20 to 80 years for electric distribution; 50 to 75 years for electric transmission; 20 to 80 years for natural gas; and 2 to 55 years for other. (b) Includes $29 million and $36 million of oil-fired generation at December 31, 2021 and 2020, respectively. (c) Original cost amounts include two CTs that have related financing obligations. The gross cumulative asset value of those agreements was $243 million and $240 million at December 31, 2021 and 2020, respectively. The total accumulated depreciation associated with the two CTs was $105 million and $99 million at December 31, 2021 and 2020, respectively. See Note 5 – Long-term Debt and Equity Financings for additional information on these agreements. (d) Renewable includes hydroelectric, wind, solar, and methane gas generation facilities. (e) Other property, plant, and equipment includes assets used to support electric and natural gas services. (f) Represents the net book value of the Rush Island Energy Center and related construction work in progress as Ameren Missouri expects to retire the energy center significantly in advance of its previously expected useful life and in the near term. See Plant to be Abandoned, Net under Note 1 – Summary of Significant Accounting Policies and NSR and Clean Air Act Litigation under Note 14 – Commitments and Contingencies for additional information on the planned accelerated retirement of the Rush Island Energy Center. Capitalized software costs are classified within “Property, Plant, and Equipment, Net” on the balance sheet and are amortized on a straight-line basis over the expected period of benefit, ranging from 2 to 15 years. The following table presents the amortization, gross carrying value, and related accumulated amortization of capitalized software by year: Amortization Expense Gross Carrying Value Accumulated Amortization 2021 2020 2019 2021 2020 2021 2020 Ameren $ 125 $ 93 $ 78 $ 1,199 $ 1,021 $ (757) $ (640) Ameren Missouri 66 44 30 523 398 (255) (189) Ameren Illinois 53 45 45 452 397 (291) (238) Annual amortization expense for capitalized software placed in service as of December 31, 2021, is estimated to be as follows: 2022 2023 2024 2025 2026 Ameren $ 135 $ 119 $ 87 $ 47 $ 21 Ameren Missouri 75 69 54 31 14 Ameren Illinois 56 47 31 14 6

Short-Term Debt And Liquidity

Short-Term Debt And Liquidity	12 Months Ended
	Dec. 31, 2021
Line of Credit Facility [Abstract]
SHORT-TERM DEBT AND LIQUIDITY	SHORT-TERM DEBT AND LIQUIDITY The liquidity needs of the Ameren Companies are typically supported through the use of available cash, drawings under committed credit agreements, commercial paper issuances, and/or, in the case of Ameren Missouri and Ameren Illinois, short-term affiliate borrowings. Short-Term Borrowings In December 2021, the Credit Agreements, which were scheduled to mature in December 2024, were extended and now mature in December 2025. The Credit Agreements provide $2.3 billion of credit cumulatively through maturity. The total facility size of the Missouri Credit Agreement and Illinois Credit Agreement is $1.2 billion and $1.1 billion, respectively. The maturity date may be extended by an additional one-year period upon the mutual consent of the borrowers and the lenders. Credit available under the agreements is provided by 22 international, national, and regional lenders, with no single lender providing more than $130 million of credit in aggregate. The obligations of each borrower under the respective Credit Agreements to which it is a party are several and not joint. Except under limited circumstances relating to expenses and indemnities, the obligations of Ameren Missouri and Ameren Illinois under the respective Credit Agreements are not guaranteed by Ameren (parent) or any other subsidiary of Ameren. The following table presents the maximum aggregate amount available to each borrower under each facility: Missouri Illinois Ameren (parent) $ 900 $ 500 Ameren Missouri 850 (a) Ameren Illinois (a) 800 (a) Not applicable. The borrowers have the option to seek additional commitments from existing or new lenders to increase the total facility size of the Credit Agreements to a maximum of $1.4 billion for the Missouri Credit Agreement and $1.3 billion for the Illinois Credit Agreement. Ameren (parent) borrowings are due and payable no later than the maturity date of the Credit Agreements. Ameren Missouri and Ameren Illinois borrowings under the applicable Credit Agreement are due and payable no later than the earlier of the maturity date or 364 days after the date of the borrowing. The obligations of the borrowers under the Credit Agreements are unsecured. Loans are available on a revolving basis under each of the Credit Agreements. Funds borrowed may be repaid and, subject to satisfaction of the conditions to borrowing, reborrowed from time to time. At the election of each borrower, the interest rates on such loans will be the alternate base rate plus the margin applicable to the particular borrower and/or the eurodollar rate plus the margin applicable to the particular borrower. The applicable margins will be determined by the borrower’s long-term unsecured credit ratings or, if no such ratings are in effect, the borrower’s corporate/issuer ratings then in effect. The borrowers have received commitments from the lenders to issue letters of credit up to $100 million under each of the Credit Agreements. In addition, the issuance of letters of credit is subject to the $2.3 billion overall combined facility borrowing limitations of the Credit Agreements. The borrowers will use the proceeds from any borrowings under the Credit Agreements for general corporate purposes, including working capital, commercial paper liquidity support, loan funding under the Ameren money pool arrangements, and other short-term affiliate loan arrangements. The Missouri Credit Agreement and the Illinois Credit Agreement are available to support issuances under Ameren (parent)’s, Ameren Missouri’s and Ameren Illinois’ commercial paper programs, respectively, subject to borrowing sublimits, as well as to support issuance of letters of credit for the borrowers. As of December 31, 2021, based on commercial paper outstanding and letters of credit issued under the Credit Agreements, along with cash and cash equivalents, the net liquidity available to Ameren (parent), Ameren Missouri, and Ameren Illinois, collectively, was $1.8 billion. The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the years ended December 31, 2021 and 2020: Ameren (parent) Ameren Missouri Ameren Illinois Ameren Consolidated 2021 Average daily amount outstanding $ 387 $ 99 $ 118 $ 604 Commercial paper issuances outstanding at period-end 277 165 103 545 Weighted-average interest rate 0.22 % 0.22 % 0.21 % 0.22 % Peak amount outstanding during period (a) $ 650 $ 546 $ 485 $ 1,134 Peak interest rate 0.38 % 0.35 % 0.35 % 0.38 % 2020 Average daily amount outstanding $ 108 $ 109 $ 46 $ 263 Commercial paper issuances outstanding at period-end 490 — — 490 Weighted-average interest rate 1.04 % 1.73 % 0.97 % 1.31 % Peak amount outstanding during period (a) $ 490 $ 573 $ 250 $ 908 Peak interest rate 3.30 % 5.05 % (b) 3.40 % 5.05 % (b) (a) The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak amount for the period. (b) Ameren’s and Ameren Missouri’s peak interest rates were affected by temporary disruptions in the commercial paper market in the first quarter of 2020. Indebtedness Provisions and Other Covenants The information below is a summary of the Ameren Companies’ compliance with indebtedness provisions and other covenants. The Credit Agreements contain conditions for borrowings and issuances of letters of credit. These conditions include the absence of default or unmatured default, material accuracy of representations and warranties (excluding any representation after the closing date as to the absence of material adverse change and material litigation, and the absence of any notice of violation, liability, or requirement under any environmental laws that could have a material adverse effect), and obtaining required regulatory authorizations. In addition, it is a condition for any Ameren Illinois borrowing that, at the time of and after giving effect to such borrowing, Ameren Illinois not be in violation of any limitation on its ability to incur unsecured indebtedness contained in its articles of incorporation. The Credit Agreements also contain nonfinancial covenants, including restrictions on the ability to incur certain liens, to transact with affiliates, to dispose of assets, to make investments in or transfer assets to its affiliates, and to merge with other entities. The Credit Agreements require each of Ameren, Ameren Missouri, and Ameren Illinois to maintain consolidated indebtedness of not more than 65% of its consolidated total capitalization pursuant to a defined calculation set forth in the agreements. As of December 31, 2021, the ratios of consolidated indebtedness to total consolidated capitalization, calculated in accordance with the provisions of the Credit Agreements, were 58%, 49%, and 45%, for Ameren, Ameren Missouri, and Ameren Illinois, respectively. The Credit Agreements contain default provisions that apply separately to each borrower. However, a default of Ameren Missouri or Ameren Illinois under the applicable credit agreement is also deemed to constitute a default of Ameren (parent) under such agreement. Defaults include a cross-default resulting from a default of such borrower under any other agreement covering outstanding indebtedness of such borrower and certain subsidiaries (other than project finance subsidiaries and nonmaterial subsidiaries) in excess of $100 million in the aggregate (including under the other credit agreement). However, under the default provisions of the Credit Agreements, any default of Ameren (parent) under either credit agreement that results solely from a default of Ameren Missouri or Ameren Illinois does not result in a cross-default of Ameren (parent) under the other credit agreement. Further, the Credit Agreements default provisions provide that an Ameren (parent) default under either of the Credit Agreements does not constitute a default by Ameren Missouri or Ameren Illinois. None of the Credit Agreements or financing agreements contain credit rating triggers that would cause a default or acceleration of repayment of outstanding balances. The Ameren Companies were in compliance with the provisions and covenants of the Credit Agreements at December 31, 2021 . Money Pools Ameren has money pool agreements with and among its subsidiaries to coordinate and provide for certain short-term cash and working capital requirements. Ameren Missouri, Ameren Illinois, and ATXI may participate in the utility money pool as both lenders and borrowers. Ameren (parent) and Ameren Services may participate in the utility money pool only as lenders. Surplus internal funds are contributed to the money pool from participants. The primary sources of external funds for the utility money pool are the Credit Agreements and the commercial paper programs. The total amount available to the pool participants from the utility money pool at any given time is reduced by the amount of borrowings made by participants, but it is increased to the extent that the pool participants advance surplus funds to the utility money pool or remit funds from other external sources. The availability of funds is also determined by funding requirement limits established by regulatory authorizations. Participants receiving a loan under the utility money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the utility money pool. The average interest rate for borrowing under the utility money pool for the year ended December 31, 2021, was 0.17% (2020 – 0.64%). See Note 13 – Related-party Transactions for the amount of interest income and expense from the utility money pool agreement recorded by Ameren Missouri and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019.

Long-Term Debt And Equity Finan

Long-Term Debt And Equity Financings	12 Months Ended
	Dec. 31, 2021
Long-Term Debt And Equity Financings [Abstract]
LONG-TERM DEBT AND EQUITY FINANCINGS	LONG-TERM DEBT AND EQUITY FINANCINGS The following table presents long-term debt outstanding, including maturities due within one year, as of December 31, 2021 and 2020: 2021 2020 Ameren (Parent): 2.50% Senior unsecured notes due 2024 $ 450 $ 450 3.65% Senior unsecured notes due 2026 350 350 1.95% Senior unsecured notes due 2027 500 — 1.75% Senior unsecured notes due 2028 450 — 3.50% Senior unsecured notes due 2031 800 800 Total long-term debt, gross 2,550 1,600 Less: Unamortized discount and premium (2) (2) Less: Unamortized debt issuance costs (15) (10) Long-term debt, net $ 2,533 $ 1,588 Ameren Missouri: Bonds and notes: 1.60% 1992 Series bonds due 2022 (a) $ 47 $ 47 3.50% Senior secured notes due 2024 (b) 350 350 2.95% Senior secured notes due 2027 (b) 400 400 3.50% First mortgage bonds due 2029 (d) 450 450 2.95% First mortgage bonds due 2030 (d) 465 465 2.15% First mortgage bonds due 2032 (d) 525 — 2.90% 1998 Series A bonds due 2033 (a) 60 60 2.90% 1998 Series B bonds due 2033 (a) 50 50 2.75% 1998 Series C bonds due 2033 (a) 50 50 5.50% Senior secured notes due 2034 (b) 184 184 5.30% Senior secured notes due 2037 (b) 300 300 8.45% Senior secured notes due 2039 (b)(c) 350 350 3.90% Senior secured notes due 2042 (b)(c) 485 485 3.65% Senior secured notes due 2045 (b) 400 400 4.00% First mortgage bonds due 2048 (d) 425 425 3.25% First mortgage bonds due 2049 (d) 330 330 2.625% First mortgage bonds due 2051 (d) 550 550 Finance obligations: City of Bowling Green agreement (Peno Creek CT) due 2022 (e) 8 16 Audrain County agreement (Audrain County CT) due 2023 (e) 240 240 Total long-term debt, gross 5,669 5,152 Less: Unamortized discount and premium (12) (12) Less: Unamortized debt issuance costs (38) (36) Less: Maturities due within one year (55) (8) Long-term debt, net $ 5,564 $ 5,096 2021 2020 Ameren Illinois: Bonds and notes: 2.70% Senior secured notes due 2022 (f)(g) $ 400 $ 400 0.375% First mortgage bonds due 2023 (h) 100 — 3.25% Senior secured notes due 2025 (f) 300 300 6.125% Senior secured notes due 2028 (f) 60 60 3.80% First mortgage bonds due 2028 (h) 430 430 1.55% First mortgage bonds due 2030 (h) 375 375 6.70% Senior secured notes due 2036 (f) 61 61 6.70% Senior secured notes due 2036 (f) 42 42 4.80% Senior secured notes due 2043 (f) 280 280 4.30% Senior secured notes due 2044 (f) 250 250 4.15% Senior secured notes due 2046 (f) 490 490 3.70% First mortgage bonds due 2047 (h) 500 500 4.50% First mortgage bonds due 2049 (h) 500 500 3.25% First mortgage bonds due 2050 (h) 300 300 2.90% First mortgage bonds due 2051 (h) 350 — Total long-term debt, gross 4,438 3,988 Less: Unamortized discount and premium (7) (6) Less: Unamortized debt issuance costs (39) (36) Less: Maturities due within one year (400) — Long-term debt, net $ 3,992 $ 3,946 ATXI: 2.45% Senior unsecured notes due 2036 (i) $ 75 $ — 3.43% Senior unsecured notes due 2050 (j) 450 450 Total long-term debt, gross 525 450 Less: Unamortized debt issuance costs (2) (2) Less: Maturities due within one year (50) — Long-term debt, net $ 473 $ 448 Ameren consolidated long-term debt, net $ 12,562 $ 11,078 (a) These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri’s senior secured notes. (b) These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the 2051 maturity of the 2.625% first mortgage bonds and the restrictions preventing a release date to occur that are attached to certain senior secured notes described in footnote (c) below, Ameren Missouri does not expect the first mortgage lien protection associated with these notes to fall away. (c) Ameren Missouri has agreed that so long as any of the 3.90% senior secured notes due 2042 are outstanding, Ameren Missouri will not permit a release date to occur, and so long as any of the 8.45% senior secured notes due 2039 are outstanding, Ameren Missouri will not optionally redeem, purchase, or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions. (d) These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri bond indenture. They are secured by substantially all Ameren Missouri property and franchises. (e) Payments due related to these financing obligations are paid to a trustee, which is authorized to utilize the cash only to pay equal amounts due to Ameren Missouri under related bonds issued by the city/county and held by Ameren Missouri. The timing and amounts of payments due from Ameren Missouri under the agreements are equal to the timing and amount of bond service payments due to Ameren Missouri, resulting in no net cash flow. The balance of both the financing obligations and the related investments in debt securities, recorded in “Other Assets,” was $248 million and $256 million, respectively, as of December 31, 2021 and 2020. (f) These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under its mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the 2051 maturity date of the 2.90% first mortgage bonds, Ameren Illinois does not expect the first mortgage lien protection associated with these notes to fall away. (g) Ameren Illinois has agreed that so long as any of the 2.70% senior secured notes due 2022 are outstanding, Ameren Illinois will not permit a release date to occur. (h) These bonds are first mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. They are secured by substantially all Ameren Illinois property and franchises. (i) The following table presents the principal maturities schedule for the 2.45% senior unsecured notes due 2036: Payment Date Principal Payment November 2029 $ 30 November 2036 45 Total $ 75 (j) The following table presents the principal maturities schedule for the 3.43% senior unsecured notes due 2050: Payment Date Principal Payment August 2022 $ 49.5 August 2024 49.5 August 2027 49.5 August 2030 49.5 August 2032 49.5 August 2038 49.5 August 2043 76.5 August 2050 76.5 Total $ 450.0 The following table presents the aggregate maturities of long-term debt, including current maturities, at December 31, 2021: Ameren (parent) (a) Ameren Missouri (a) Ameren Illinois (a) ATXI (a) Ameren Consolidated (a) 2022 $ — $ 55 $ 400 $ 50 $ 505 2023 — 240 100 — 340 2024 450 350 — 50 850 2025 — — 300 — 300 2026 350 — — — 350 Thereafter 1,750 5,024 3,638 425 10,837 Total $ 2,550 $ 5,669 $ 4,438 $ 525 $ 13,182 (a) Excludes unamortized discount, premium, and debt issuance costs of $17 million, $50 million, $46 million, and $2 million at Ameren (parent), Ameren Missouri, Ameren Illinois, and ATXI, respectively. All classes of Ameren Missouri’s and Ameren Illinois’ preferred stock are entitled to cumulative dividends, have voting rights, and are not subject to mandatory redemption. The preferred stock of Ameren’s subsidiaries is included in “Noncontrolling Interests” on Ameren’s consolidated balance sheet. The following table presents the outstanding preferred stock of Ameren Missouri and Ameren Illinois, which is redeemable at the option of the issuer, at the prices shown below as of December 31, 2021 and 2020: Shares Outstanding Redemption Price (per share) 2021 2020 Ameren Missouri: Without par value and stated value of $100 per share, 25 million shares authorized $3.50 Series 130,000 shares $ 110.00 $ 13 $ 13 $3.70 Series 40,000 shares 104.75 4 4 $4.00 Series 150,000 shares 105.625 15 15 $4.30 Series 40,000 shares 105.00 4 4 $4.50 Series 213,595 shares 110.00 (a) 21 21 $4.56 Series 200,000 shares 102.47 20 20 $4.75 Series 20,000 shares 102.176 2 2 $5.50 Series A 14,000 shares 110.00 1 1 Total $ 80 $ 80 Ameren Illinois: With par value of $100 per share, 2 million shares authorized 4.00% Series 144,275 shares $ 101.00 $ 14 $ 14 4.08% Series 45,224 shares 103.00 5 5 4.20% Series 23,655 shares 104.00 2 2 4.25% Series 50,000 shares 102.00 5 5 4.26% Series 16,621 shares 103.00 2 2 4.42% Series 16,190 shares 103.00 2 2 4.70% Series 18,429 shares 104.30 2 2 4.90% Series 73,825 shares 102.00 7 7 4.92% Series 49,289 shares 103.50 5 5 5.16% Series 50,000 shares 102.00 5 5 6.625% Series (b) 100.00 — 12 7.75% Series (b) 100.00 — 1 Total $ 49 $ 62 Total Ameren $ 129 $ 142 (a) In the event of voluntary liquidation, $105.50. (b) In March 2021, Ameren Illinois redeemed its 6.625% and 7.75% series preferred stock at par. Ameren has 100 million shares of $0.01 par value preferred stock authorized, with no such shares outstanding. Ameren Missouri has 7.5 million shares of $1 par value preference stock authorized, with no such shares outstanding. Ameren Illinois has 2.6 million shares of no par value preferred stock authorized, with no such shares outstanding. Ameren Under the DRPlus and its 401(k) plan, Ameren issued 0.5 million, 0.7 million, and 0.9 million shares of common stock in 2021, 2020, and 2019, respectively, and received proceeds of $47 million, $51 million, and $68 million for the respective years. In addition, Ameren issued 0.5 million, 0.5 million, and 0.8 million shares of common stock valued at $33 million, $38 million, and $54 million in 2021, 2020, 2019, respectively, for no cash consideration in connection with stock-based compensation. In May 2020, Ameren filed a Form S-3 registration statement with the SEC, authorizing the offering of 4 million additional shares of its common stock under the DRPlus, which expires in May 2023. Shares of common stock sold under the DRPlus are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated transactions. In October 2020, Ameren, Ameren Missouri, and Ameren Illinois filed a Form S-3 shelf registration statement with the SEC, registering the issuance of an unspecified amount of certain types of securities. This registration statement expires in October 2023. In October 2018, Ameren filed a Form S-8 registration statement with the SEC, authorizing the offering of 4 million additional shares of its common stock under its 401(k) plan. Shares of common stock issuable under the 401(k) plan are, at Ameren’s option, newly issued shares, treasury shares, or shares purchased in the open market or in privately negotiated transactions. In May 2021, Ameren entered into an equity distribution sales agreement pursuant to which Ameren may offer and sell from time to time up to $750 million of its common stock through an ATM program, which includes the ability to enter into forward sales agreements. During 2021, Ameren issued 1.8 million shares of common stock and received proceeds of $148 million. These proceeds were net of less than $2 million in compensation paid to selling agents. There were no shares issued through the ATM program for the three months ended December 31, 2021. In September 2021, December 2021, and January 2022, Ameren entered into forward sale agreements under the ATM program with counterparties relating to 0.4 million, 0.5 million, and 0.2 million shares of common stock, respectively. The September 2021, December 2021, and January 2022 forward sale agreements can be settled at Ameren’s discretion on or prior to May 3, 2023, June 30, 2023, and June 30, 2023, respectively. On a settlement date or dates, if Ameren elects to physically settle the forward sale agreement, Ameren will issue shares of common stock to the counterparties at the then-applicable forward sale price. The forward sale price was initially $87.87, $87.03, and $88.10 per share, for the September 2021, December 2021, and January 2022 forward sale agreements, respectively. Each initial forward sale price is subject to adjustment based on a floating interest rate factor equal to the overnight bank funding rate less a spread of 75 basis points, and will be subject to decrease on certain dates specified in the forward sale agreements by specified amounts related to expected dividends on shares of the common stock during the term of the forward sale agreements. If the overnight bank funding rate is less than the spread on any day, the interest rate factor will result in a reduction of the forward sale price. The forward sale agreements will be physically settled unless Ameren elects to settle in cash or to net share settle. At December 31, 2021, Ameren could have settled the September 2021 and December 2021 forward sale agreements with physical delivery of 0.4 million and 0.5 million shares of common stock, respectively, to the counterparty in exchange for cash of $30 million and $41 million, respectively. The forward sale agreements have been classified as equity transactions. In August 2019, Ameren entered into a forward sale agreement with a counterparty relating to 7.5 million shares of common stock. In December 2020, pursuant to the agreement terms, Ameren partially settled the forward sale agreement by physically delivering 5.9 million shares of common stock for cash proceeds of $425 million. In February 2021, Ameren settled the remainder of the forward sale agreement by physically delivering 1.6 million shares of common stock for cash proceeds of $113 million. The proceeds were used to fund a portion of Ameren Missouri’s wind generation investments. See Note 15 – Supplemental Information for additional information about the wind generation facilities. In March 2021, Ameren (parent) issued $450 million of 1.75% senior unsecured notes due March 2028, with interest payable semiannually on March 15 and September 15 of each year, beginning September 15, 2021. Ameren received net proceeds of $447 million which were used for general corporate purposes, including the repayment of short-term debt. In November 2021, Ameren (parent) issued $500 million of 1.95% senior unsecured notes due March 2027, with interest payable semiannually on March 15 and September 15 of each year, beginning March 15, 2022. Ameren received net proceeds of $497 million which were used to repay short-term debt. In April 2020, Ameren (parent) issued $800 million of 3.50% senior unsecured notes due January 2031, with interest payable semiannually on January 15 and July 15 of each year, beginning July 15, 2020. Ameren received net proceeds of $793 million, which were used for general corporate purposes, including to repay outstanding short-term debt, and were used to fund the repayment of Ameren’s $350 million of 2.70% senior unsecured notes, which were redeemed at par plus accrued interest in October 2020. Ameren Missouri In June 2021, Ameren Missouri issued $525 million of 2.15% first mortgage bonds due March 2032, with interest payable semiannually on March 15 and September 15 of each year, beginning March 15, 2022. Ameren Missouri received net proceeds of $521 million, which were used to repay short-term debt and for near-term capital expenditures. Ameren Missouri intends to allocate an amount equal to the net proceeds to sustainability projects meeting certain eligibility criteria. In March 2020, Ameren Missouri issued $465 million of 2.95% first mortgage bonds due March 2030, with interest payable semiannually on March 15 and September 15 of each year, beginning September 15, 2020. Ameren Missouri received net proceeds of $462 million, which were used to repay outstanding short-term debt, including short-term debt that Ameren Missouri incurred in connection with the repayment of $85 million of its 5.00% senior secured notes that matured in February 2020. In October 2020, Ameren Missouri issued $550 million of 2.625% first mortgage bonds due March 2051, with interest payable semiannually on March 15 and September 15 of each year, beginning March 15, 2021. Ameren Missouri received net proceeds of $543 million, which were allocated and used to partially finance the acquisition of two wind generation energy centers. See Note 15 – Supplemental Information for information about the wind generation energy centers. For information on Ameren Missouri’s capital contributions, refer to Capital Contributions in Note 13 – Related-party Transactions. Ameren Illinois In March 2021, Ameren Illinois redeemed its 6.625% and 7.75% series preferred stock at par for $12 million and $1 million, respectively. The preferred stock of Ameren Illinois is reflected in “Noncontrolling Interests” on Ameren’s consolidated balance sheet. In June 2021, Ameren Illinois issued $350 million of 2.90% first mortgage bonds due June 2051, with interest payable semiannually on June 15 and December 15 of each year, beginning December 15, 2021. Ameren Illinois received net proceeds of $345 million, which were used to repay short-term debt. Ameren Illinois intends to allocate an amount equal to the net proceeds to sustainability projects meeting certain eligibility criteria. In June 2021, Ameren Illinois issued $100 million of 0.375% first mortgage bonds due June 2023, with interest payable semiannually on June 15 and December 15 of each year, beginning December 15, 2021. Ameren Illinois received net proceeds of $100 million, which were used to repay short-term debt. In November 2020, Ameren Illinois issued $375 million of 1.55% first mortgage bonds due November 2030, with interest payable semiannually on May 15 and November 15 of each year, beginning May 15, 2021. Ameren Illinois received net proceeds of $371 million, which were used to repay short-term debt. For information on Ameren Illinois’ capital contributions, refer to Capital Contributions in Note 13 – Related-party Transactions. ATXI In November 2021, pursuant to a note purchase agreement, ATXI issued $75 million of its 2.45% senior unsecured notes due 2036, with interest payable semiannually on May 16 and November 16 of each year, beginning May 16, 2022, through a private placement offering exempt from registration under the Securities Act of 1933, as amended. ATXI received net proceeds of $75 million, which were used to refinance a portion of an intercompany long-term note with Ameren (parent) and to repay short-term debt. In November 2021, pursuant to a note purchase agreement, ATXI agreed to issue $95 million of its 2.96% senior unsecured notes due 2052, with interest payable semiannually on February 25 and August 25 of each year, beginning February 25, 2023, through a private placement offering exempt from registration under the Securities Act of 1933, as amended. ATXI expects to issue the notes and receive net proceeds of $95 million in August 2022, which will be used to refinance the remaining portion of an intercompany long-term note with Ameren (parent), repay a $50 million principal payment of its 3.43% senior unsecured notes, and to repay short-term debt. Indenture Provisions and Other Covenants Ameren Missouri’s and Ameren Illinois’ indentures and articles of incorporation include covenants and provisions related to issuances of first mortgage bonds and preferred stock. Ameren Missouri and Ameren Illinois are required to meet certain ratios to issue additional first mortgage bonds and preferred stock. A failure to achieve these ratios would not result in a default under these covenants and provisions but would restrict the companies’ ability to issue bonds or preferred stock. The following table summarizes the required and actual interest coverage ratios for interest charges, dividend coverage ratios, and bonds and preferred stock issuable as of December 31, 2021, at an assumed interest rate of 5% and dividend rate of 6%. Required Interest Coverage Ratio (a) Actual Interest Bonds Issuable (b) Required Dividend Coverage Ratio (c) Actual Dividend Preferred Stock Ameren Missouri > 2.0 3.2 $4,834 > 2.5 152.4 $3,418 Ameren Illinois > 2.0 7.3 7,697 > 1.5 3.5 203 (d) (a) Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds. (b) Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $2,437 million and $643 million at Ameren Missouri and Ameren Illinois, respectively. (c) Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation. (d) Preferred stock issuable is restricted by the amount of preferred stock that is currently authorized by Ameren Illinois’ articles of incorporation. Ameren’s indenture does not require Ameren to comply with any quantitative financial covenants. The indenture does, however, include certain cross-default provisions. Specifically, either (1) the failure by Ameren to pay when due and upon expiration of any applicable grace period any portion of any Ameren indebtedness in excess of $25 million, or (2) the acceleration upon default of the maturity of any Ameren indebtedness in excess of $25 million under any indebtedness agreement, including borrowings under the Credit Agreements or the Ameren commercial paper program, constitutes a default under the indenture, unless such past due or accelerated debt is discharged or the acceleration is rescinded or annulled within a specified period. Ameren Missouri and Ameren Illinois and certain other nonregistrant Ameren subsidiaries are subject to Section 305(a) of the Federal Power Act, which makes it unlawful for any officer or director of a public utility, as defined in the Federal Power Act, to participate in the making or paying of any dividend from any funds “properly included in capital account.” The FERC has consistently interpreted the provision to allow dividends to be paid as long as (1) the source of the dividends is clearly disclosed, (2) the dividends are not excessive, and (3) there is no self-dealing on the part of corporate officials. At a minimum, Ameren believes that dividends can be paid by its subsidiaries that are public utilities from net income and retained earnings. In addition, under Illinois law, Ameren Illinois and ATXI may not pay any dividend on their respective stock unless, among other things, their respective earnings and earned surplus are sufficient to declare and pay a dividend after provisions are made for reasonable and proper reserves, or unless Ameren Illinois or ATXI has specific authorization from the ICC. Ameren Illinois’ articles of incorporation require dividend payments on its common stock to be based on ratios of common stock to total capitalization and other provisions related to certain operating expenses and accumulations of earned surplus. Ameren Illinois has made a commitment to the FERC to maintain a minimum 30% ratio of common stock equity to total capitalization. As of December 31, 2021, using the FERC-agreed upon calculation method, Ameren Illinois’ ratio of common stock equity to total capitalization was 54%. ATXI’s note purchase agreements includes financial covenants that require ATXI not to permit at any time (1) debt to exceed 70% of total capitalization or (2) secured debt to exceed 10% of total assets. At December 31, 2021, the Ameren Companies were in compliance with the provisions and covenants contained in their indentures and articles of incorporation, as applicable, and ATXI was in compliance with the provisions and covenants contained in its note purchase agreements. In order for the Ameren Companies to issue securities in the future, they will have to comply with all applicable requirements in effect at the time of any such issuances. Off-Balance-Sheet Arrangements At December 31, 2021, none of the Ameren Companies had any significant off-balance-sheet financing arrangements, other than variable interest entities and the September and December 2021 forward sale agreements relating to common stock. See Note 1 – Summary of Significant Accounting Policies for further detail concerning variable interest entities.

Other Income, Net

Other Income, Net	12 Months Ended
	Dec. 31, 2021
Other Nonoperating Income (Expense) [Abstract]
OTHER INCOME AND EXPENSES	OTHER INCOME, NET The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren: Other Income, Net Allowance for equity funds used during construction $ 43 $ 32 $ 28 Interest income on industrial development revenue bonds 25 25 25 Other interest income 2 4 8 Non-service cost components of net periodic benefit income (a) 136 116 90 Miscellaneous income 22 13 6 Donations (9) (25) (b) (12) Miscellaneous expense (17) (14) (15) Total Other Income, Net $ 202 $ 151 $ 130 Ameren Missouri: Other Income, Net Allowance for equity funds used during construction $ 26 $ 19 $ 19 Interest income on industrial development revenue bonds 25 25 25 Other interest income 1 1 1 Non-service cost components of net periodic benefit income (a) 55 46 18 Miscellaneous income 3 4 5 Donations (4) (12) (b) (3) Miscellaneous expense (7) (7) (7) Total Other Income, Net $ 99 $ 76 $ 58 2021 2020 2019 Ameren Illinois: Other Income, Net Allowance for equity funds used during construction $ 17 $ 13 $ 9 Interest income 1 3 6 Non-service cost components of net periodic benefit income (a) 55 48 47 Miscellaneous income 6 6 3 Donations (5) (5) (5) Miscellaneous expense (8) (6) (7) Total Other Income, Net $ 66 $ 59 $ 53 (a) For the years ended December 31, 2021, 2020, and 2019, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(7) million, $(4) million, and $29 million, respectively, due to a tracker for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. (b) Includes $8 million pursuant to Ameren Missouri’s March 2020 electric rate order.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
DERIVATIVE FINANCIAL INSTRUMENTS	DERIVATIVE FINANCIAL INSTRUMENTS We use derivatives to manage the risk of changes in market prices for natural gas, power, and uranium, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following: • an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices; • market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; • actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and • actual off-system sales revenues that differ from anticipated revenues. The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty. All contracts considered to be derivative instruments are required to be recorded on the balance sheet at their fair values, unless the NPNS exception applies. See Note 8 – Fair Value Measurements for discussion of our methods of assessing the fair value of derivative instruments. Many of our physical contracts, such as our purchased power contracts, qualify for the NPNS exception to derivative accounting rules. The revenue or expense on NPNS contracts is recognized at the contract price upon physical delivery. The following disclosures exclude NPNS contracts and other nonderivative commodity contracts that are accounted for under the accrual method of accounting. If we determine that a contract meets the definition of a derivative and is not eligible for the NPNS exception, we review the contract to determine whether the resulting gains or losses qualify for regulatory deferral. Derivative contracts that qualify for regulatory deferral are recorded at fair value, with changes in fair value recorded as regulatory assets or liabilities in the period in which the change occurs. We believe derivative losses and gains deferred as regulatory assets and liabilities are probable of recovery, or refund, through future rates charged to customers. Regulatory assets and liabilities are amortized to operating income as related losses and gains are reflected in rates charged to customers. Therefore, gains and losses on these derivatives have no effect on operating income. As of December 31, 2021 and 2020, all contracts that met the definition of a derivative and were not eligible for the NPNS exception received regulatory deferral. Cash flows for all derivative financial instruments are classified in cash flows from operating activities. The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2021 and 2020. As of December 31, 2021, these contracts extended through October 2024, October 2026, May 2032, and March 2024 for fuel oils, natural gas, power, and uranium, respectively. Quantity (in millions, except as indicated) 2021 2020 Commodity Ameren Missouri Ameren Ameren Ameren Missouri Ameren Ameren Fuel oils (in gallons) 30 — 30 43 — 43 Natural gas (in mmbtu) 35 144 179 33 114 147 Power (in MWhs) 6 6 12 6 7 13 Uranium (pounds in thousands) 586 — 586 365 — 365 The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of December 31, 2021 and 2020: 2021 2020 Commodity Balance Sheet Location Ameren Ameren Ameren Ameren Ameren Ameren Fuel oils Other current assets $ 8 $ — $ 8 $ 2 $ — $ 2 Other assets 5 — 5 — — — Natural gas Other current assets 7 28 35 1 8 9 Other assets 5 13 18 2 2 4 Power Other current assets 23 — 23 7 — 7 Uranium Other assets 1 — 1 — — — Total assets $ 49 $ 41 $ 90 $ 12 $ 10 $ 22 Fuel oils Other current liabilities $ — $ — $ — $ 7 $ — $ 7 Other deferred credits and liabilities — — — 2 — 2 Natural gas Other current liabilities 2 6 8 1 1 2 Other deferred credits and liabilities 1 2 3 — 1 1 Power Other current liabilities 50 9 59 3 17 20 Other deferred credits and liabilities 23 108 131 8 181 189 Uranium Other current liabilities 1 — 1 — — — Total liabilities $ 77 $ 125 $ 202 $ 21 $ 200 $ 221 We believe that entering into master netting arrangements or similar agreements mitigates the level of financial loss that could result from default by allowing net settlement of derivative assets and liabilities. These master netting arrangements allow the counterparties to net settle sale and purchase transactions. Further, collateral requirements are calculated at the master netting arrangement or similar agreement level by counterparty. The following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of December 31, 2021. If the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted at December 31, 2020, the net amounts would not be materially different from the gross amounts. Gross Amounts Not Offset in the Balance Sheet Commodity Contracts Eligible to be Offset Gross Amounts Recognized in the Balance Sheet Derivative Instruments Cash Collateral Received/Posted (a) Net 2021 Assets: Ameren Missouri $ 49 $ 15 $ — $ 34 Ameren Illinois 41 4 — 37 Ameren $ 90 $ 19 $ — $ 71 Liabilities: Ameren Missouri $ 77 $ 15 $ 47 $ 15 Ameren Illinois 125 4 — 121 Ameren $ 202 $ 19 $ 47 $ 136 (a) Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” on Ameren’s balance sheet and in “Current collateral assets” on Ameren Missouri’s balance sheet. Credit Risk In determining our concentrations of credit risk related to derivative instruments, we review our individual counterparties and categorize each counterparty into groupings according to the primary business in which each engages. As of December 31, 2021, if counterparty groups were to fail completely to perform on contracts, Ameren’s, Ameren Missouri’s, and Ameren Illinois’ maximum exposure related to derivative assets, predominantly from financial institutions, was $77 million, $36 million, and $41 million, respectively. The potential loss on counterparty exposures may be reduced or eliminated by the application of master netting arrangements or similar agreements and collateral held. As of December 31, 2021, the potential loss after consideration of the application of master netting arrangements or similar agreements and collateral held for Ameren, Ameren Missouri, and Ameren Illinois was $61 million, $23 million, and $38 million, respectively. Certain of our derivative instruments contain collateral provisions tied to the Ameren Companies’ credit ratings. If our credit ratings were downgraded below investment grade, or if a counterparty with reasonable grounds for uncertainty regarding our ability to satisfy an obligation requested adequate assurance of performance, additional collateral postings might be required. The additional collateral required is the net liability position allowed under the master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered and (2) those counterparties with rights to do so requested collateral. As of December 31, 2021, the aggregate fair value of derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that counterparties could require were each immaterial to Ameren, Ameren Missouri, and Ameren Illinois.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Fair value is defined as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. We use various methods to determine fair value, including market, income, and cost approaches. With these approaches, we adopt certain assumptions that market participants would use in pricing the asset or liability, including assumptions about market risk or the risks inherent in the inputs to the valuation. Inputs to valuation can be readily observable, market-corroborated, or unobservable. We use valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. Authoritative accounting guidance established a fair value hierarchy that prioritizes the inputs used to measure fair value. All financial assets and liabilities carried at fair value are classified and disclosed in one of the following three hierarchy levels: Level 1 (quoted prices in active markets for identical assets or liabilities): Inputs based on quoted prices in active markets for identical assets or liabilities. Level 1 assets and liabilities are primarily exchange-traded derivatives, cash and cash equivalents, and listed equity securities. The market approach is used to measure the fair value of equity securities held in Ameren Missouri’s nuclear decommissioning trust fund. Equity securities in this fund are representative of the S&P 500 index, excluding securities of Ameren Corporation, owners and/or operators of nuclear power plants, and the trustee and investment managers. The S&P 500 index comprises stocks of large-capitalization companies. Level 2 (significant other observable inputs) : Market-based inputs corroborated by third-party brokers or exchanges based on transacted market data. Level 2 assets and liabilities include certain assets held in Ameren Missouri’s nuclear decommissioning trust fund, including United States Treasury and agency securities, corporate bonds and other fixed-income securities, and certain over-the-counter derivative instruments, including natural gas and financial power transactions. Fixed income securities are valued by using prices from independent industry-recognized data vendors who provide values that are either exchange-based or matrix-based. The fair value measurements of fixed-income securities classified as Level 2 are based on inputs other than quoted prices that are observable for the asset or liability. Examples are matrix pricing, market corroborated pricing, and inputs such as yield curves and indices. Derivative instruments classified as Level 2 are valued by corroborated observable inputs, such as pricing services or prices from similar instruments that trade in liquid markets. Our development and corroboration process entails obtaining multiple quotes or prices from outside sources. To derive our forward view to price our derivative instruments at fair value, we average the bid/ask spreads to the midpoints. Additionally, a review of all sources is performed to identify any anomalies or potential errors. Further, we consider the volume of transactions on certain trading platforms in our reasonableness assessment of the averaged midpoints. The value of natural gas derivative contracts is based upon exchange closing prices without significant unobservable adjustments. The value of power derivative contracts is based upon exchange closing prices or the use of multiple forward prices provided by third parties. Level 3 (significant other unobservable inputs): Unobservable inputs that are not corroborated by market data. Level 3 assets and liabilities are valued by internally developed models and assumptions or methodologies that use significant unobservable inputs. Level 3 assets and liabilities include derivative instruments that trade in less liquid markets, where pricing is largely unobservable. We value Level 3 instruments by using pricing models with inputs that are often unobservable in the market, such as certain internal assumptions, quotes or prices from outside sources not supported by a liquid market, or trend rates. We perform an analysis each quarter to determine the appropriate hierarchy level of the assets and liabilities subject to fair value measurements. Financial assets and liabilities are classified in their entirety according to the lowest level of input that is significant to the fair value measurement. All assets and liabilities whose fair value measurement is based on significant unobservable inputs are classified as Level 3. We consider nonperformance risk in our valuation of derivative instruments by analyzing our own credit standing and the credit standing of our counterparties, and by considering any credit enhancements (e.g., collateral). Included in our valuation, and based on current market conditions, is a valuation adjustment for counterparty default derived from market data such as the price of credit default swaps, bond yields, and credit ratings. No material gains or losses related to valuation adjustments for counterparty default risk were recorded at Ameren, Ameren Missouri, or Ameren Illinois in 2021, 2020, or 2019. At December 31, 2021 and 2020, the counterparty default risk valuation adjustment related to derivative contracts was immaterial for Ameren, Ameren Missouri, and Ameren Illinois. The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets: Ameren Missouri Derivative assets – commodity contracts: Fuel oils $ 13 $ — $ — $ 13 $ — $ — $ 2 $ 2 Natural gas — 12 — 12 — 3 — 3 Power 10 — 13 23 2 — 5 7 Uranium — — 1 1 — — — — Total derivative assets – commodity contracts $ 23 $ 12 $ 14 $ 49 $ 2 $ 3 $ 7 $ 12 Nuclear decommissioning trust fund: Equity securities: U.S. large capitalization $ 824 $ — $ — $ 824 $ 680 $ — $ — $ 680 Debt securities: U.S. Treasury and agency securities — 141 — 141 — 115 — 115 Corporate bonds — 131 — 131 — 115 — 115 Other — 56 — 56 — 67 — 67 Total nuclear decommissioning trust fund $ 824 $ 328 $ — $ 1,152 (a) $ 680 $ 297 $ — $ 977 (a) Total Ameren Missouri $ 847 $ 340 $ 14 $ 1,201 $ 682 $ 300 $ 7 $ 989 Ameren Illinois Derivative assets – commodity contracts: Natural gas $ 1 $ 33 $ 7 $ 41 $ — $ 6 $ 4 $ 10 Ameren Derivative assets – commodity contracts (b) $ 24 $ 45 $ 21 $ 90 $ 2 $ 9 $ 11 $ 22 Nuclear decommissioning trust fund (c) 824 328 — 1,152 (a) 680 297 — 977 (a) Total Ameren $ 848 $ 373 $ 21 $ 1,242 $ 682 $ 306 $ 11 $ 999 Liabilities: Ameren Missouri Derivative liabilities – commodity contracts: Fuel oils $ — $ — $ — $ — $ 6 $ — $ 3 $ 9 Natural gas — 2 1 3 — 1 — 1 Power 45 — 28 73 8 — 3 11 Uranium — — 1 1 — — — — Total Ameren Missouri $ 45 $ 2 $ 30 $ 77 $ 14 $ 1 $ 6 $ 21 Ameren Illinois Derivative liabilities – commodity contracts: Natural gas $ — $ 5 $ 3 $ 8 $ — $ 1 $ 1 $ 2 Power — — 117 117 — — 198 198 Total Ameren Illinois $ — $ 5 $ 120 $ 125 $ — $ 1 $ 199 $ 200 Ameren Derivative liabilities – commodity contracts (b) $ 45 $ 7 $ 150 $ 202 $ 14 $ 2 $ 205 $ 221 (a) Balance excludes $7 million and $5 million of cash and cash equivalents, receivables, payables, and accrued income, net for December 31, 2021 and 2020, respectively. (b) See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity. (c) See the Ameren Missouri section of the table for a breakout of Ameren’s nuclear decommissioning trust fund by investment type. See Note 10 – Retirement Benefits for tables that set forth, by level within the fair value hierarchy, Ameren’s pension and postretirement plan assets as of December 31, 2021 and 2020. Level 3 fuel oils, natural gas and uranium derivative contract assets and liabilities measured at fair value on a recurring basis were immaterial for all periods presented. The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the years ended December 31, 2021 and 2020: 2021 2020 Ameren Ameren Ameren Ameren Ameren Ameren Beginning balance at January 1 $ 2 $ (198) $ (196) $ 13 $ (224) $ (211) Realized and unrealized gains (losses) included in regulatory assets/liabilities (1) 70 69 15 8 23 Settlements (16) 11 (5) (26) 18 (8) Ending balance at December 31 $ (15) $ (117) $ (132) $ 2 $ (198) $ (196) Change in unrealized gains (losses) related to assets/liabilities held at December 31 $ (14) $ 65 $ 51 $ 1 $ 9 $ 10 All gains or losses related to our Level 3 derivative commodity contracts are expected to be recovered or returned through customer rates; therefore, there is no impact to either net income or other comprehensive income resulting from changes in the fair value of these instruments. The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of December 31, 2021 and 2020: Fair Value Weighted Average (b) Commodity Assets Liabilities Valuation Technique(s) Unobservable Input (a) Range 2021 Power (c) $ 13 $ (145) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 32 – 55 40 Nodal basis ($/MWh) (14) – 0 (2) Trend rate (%) 0 – 0 0 2020 Power (c) $ 5 $ (201) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 23 – 37 29 Nodal basis ($/MWh) (6) – 0 (2) Trend rate (%) 2 – 6 3 (a) Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement. (b) Unobservable inputs were weighted by relative fair value. (c) Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials. The following table sets forth, by level within the fair value hierarchy, the carrying amount and fair value of financial assets and liabilities disclosed, but not carried, at fair value as of December 31, 2021 and 2020: Carrying Fair Value Level 1 Level 2 Level 3 Total December 31, 2021 Ameren: Cash, cash equivalents, and restricted cash $ 155 $ 155 $ — $ — $ 155 Investments in industrial development revenue bonds (a) 248 — 248 — 248 Short-term debt 545 — 545 — 545 Long-term debt (including current portion) (a) 13,067 (b) — 13,930 591 (c) 14,521 Ameren Missouri: Cash, cash equivalents, and restricted cash $ 8 $ 8 $ — $ — $ 8 Investments in industrial development revenue bonds (a) 248 — 248 — 248 Short-term debt 165 — 165 — 165 Long-term debt (including current portion) (a) 5,619 (b) — 6,321 — 6,321 Ameren Illinois: Cash, cash equivalents, and restricted cash $ 133 $ 133 $ — $ — $ 133 Short-term debt 103 — 103 — 103 Long-term debt (including current portion) 4,392 (b) — 4,971 — 4,971 December 31, 2020 Ameren: Cash, cash equivalents, and restricted cash $ 301 $ 301 $ — $ — $ 301 Investments in industrial development revenue bonds (a) 256 — 256 — 256 Short-term debt 490 — 490 — 490 Long-term debt (including current portion) (a) 11,086 (b) — 12,778 537 (c) 13,315 Ameren Missouri: Cash, cash equivalents, and restricted cash $ 145 $ 145 $ — $ — $ 145 Advances to money pool 139 — 139 — 139 Investments in industrial development revenue bonds (a) 256 — 256 — 256 Long-term debt (including current portion) (a) 5,104 (b) — 6,160 — 6,160 Ameren Illinois: Cash, cash equivalents, and restricted cash $ 147 $ 147 $ — $ — $ 147 Borrowings from money pool 19 — 19 — 19 Long-term debt (including current portion) 3,946 (b) — 4,822 — 4,822 (a) Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of December 31, 2021 and 2020, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value. (b) Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $94 million, $38 million, and $39 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2021. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $84 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2020. (c) The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

Callaway Energy Center

Callaway Energy Center	12 Months Ended
	Dec. 31, 2021
Nuclear Waste Matters [Abstract]
CALLAWAY ENERGY CENTER	CALLAWAY ENERGY CENTER Maintenance Outage During its return to full power after the completion of the last refueling and maintenance outage in late December 2020, the Callaway Energy Center experienced a non-nuclear operating issue related to its generator. After replacement of certain key components of the generator, the energy center returned to service in early August 2021. The cost of generator repairs was approximately $60 million, which was largely capital expenditures. In April 2021, Ameren Missouri’s insurance claims were accepted by NEIL, which covered a significant portion of the capital expenditures and covered lost sales of up to $4.5 million weekly after March 17, 2021. Insurance recoveries related to lost sales were reflected in electric operating revenues and included in net energy costs under the FAC. Expected insurance recoveries related to the capital expenditures were reflected as a reduction to property, plant, and equipment. As of December 31, 2021, a $33 million insurance receivable was included in “Miscellaneous accounts receivable” on Ameren’s and Ameren Missouri’s balance sheets related to the capital expenditures and lost sales insurance claims. In January 2022, Ameren Missouri received $17 million in payments from NEIL and EMANI related to the capital expenditures insurance claims. Spent Nuclear Fuel Under the Nuclear Waste Policy Act of 1982, as amended, the DOE is responsible for disposing of spent nuclear fuel from the Callaway Energy Center and other commercial nuclear energy centers. As required by the act, Ameren Missouri and other utilities have entered into standard contracts with the DOE, which stated that the DOE would begin to dispose of spent nuclear fuel by 1998. However, the DOE failed to fulfill its disposal obligations, and Ameren Missouri and other nuclear energy center owners sued the DOE to recover costs incurred for ongoing storage of their spent fuel. Ameren Missouri’s lawsuit against the DOE resulted in a settlement agreement that provides for annual reimbursement of additional spent fuel storage and related costs. Ameren Missouri received immaterial reimbursements from the DOE in the years ended December 31, 2021, 2020, and 2019. Ameren Missouri will continue to apply for reimbursement from the DOE for allowable costs associated with the ongoing storage of spent fuel. The DOE’s delay in carrying out its obligation to dispose of spent nuclear fuel from the Callaway Energy Center is not expected to adversely affect the continued operations of the energy center. Decommissioning Electric rates charged to customers provide for the recovery of the Callaway Energy Center’s decommissioning costs, which include decontamination, dismantling, and site restoration costs, over the expected life of the nuclear energy center. Amounts collected from customers are deposited into the external nuclear decommissioning trust fund to provide for the Callaway Energy Center’s decommissioning. It is assumed that the Callaway Energy Center site will be decommissioned after its retirement through the immediate dismantlement method and removed from service. The Callaway Energy Center’s operating license expires in 2044. Ameren and Ameren Missouri have recorded an ARO for the Callaway Energy Center decommissioning costs at fair value. Annual decommissioning costs of $7 million are included in the costs used to establish electric rates for Ameren Missouri’s customers. Every three years, the MoPSC requires Ameren Missouri to file an updated cost study and funding analysis for decommissioning its Callaway Energy Center. An updated cost study and funding analysis was filed with the MoPSC in November 2020 and reflected within the ARO. In February 2021, the MoPSC approved no change in electric rates for decommissioning costs consistent with Ameren Missouri’s updated cost study and funding analysis. Ameren and Ameren Missouri have classified the investments in debt and equity securities that are held in the nuclear decommissioning trust fund as available for sale, and have recorded all such investments at their fair market value at December 31, 2021 and 2020. Investments in the nuclear decommissioning trust fund have a target allocation of 60% to 70% in equity securities, with the balance invested in debt securities. The fair value of the trust fund for Ameren Missouri’s Callaway Energy Center is reported as “Nuclear decommissioning trust fund” in Ameren’s and Ameren Missouri’s balance sheets. This amount is legally restricted and may be used only to fund the costs of nuclear decommissioning. Changes in the fair value of the trust fund are recorded as an increase or decrease to the nuclear decommissioning trust fund, with an offsetting adjustment to the regulatory liability related to AROs. This reporting is consistent with the method used to account for the decommissioning costs recovered in rates. See Note 2 – Rate and Regulatory Matters for the regulatory liability recorded at December 31, 2021. If the assumed return on trust assets is not earned, Ameren Missouri believes that it is probable that any additional funding requirements resulting from such earnings deficiency will be recovered in customer rates. The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Proceeds from sales and maturities $ 439 $ 183 $ 260 Gross realized gains 32 10 10 Gross realized losses 6 3 2 The following table presents the cost and fair value of investments in debt and equity securities in Ameren’s and Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2021 and December 31, 2020: Security Type Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value 2021 Debt securities $ 320 $ 10 $ 2 $ 328 Equity securities 188 640 4 824 Cash and cash equivalents 4 — — 4 Other (a) 3 — — 3 Total $ 515 $ 650 $ 6 $ 1,159 2020 Debt securities $ 272 $ 25 $ — $ 297 Equity securities 198 491 9 680 Cash and cash equivalents 4 — — 4 Other (a) 1 — — 1 Total $ 475 $ 516 $ 9 $ 982 (a) Represents net receivables and payables relating to pending securities sales, interest, and securities purchases. The following table presents the costs and fair values of investments in debt securities in Ameren’s and Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2021: Cost Fair Value Less than 5 years $ 155 $ 156 5 years to 10 years 71 72 Due after 10 years 94 100 Total $ 320 $ 328 Insurance The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at January 1, 2022: Type and Source of Coverage Most Recent Maximum Coverages Maximum Assessments Public liability and nuclear worker liability: American Nuclear Insurers January 1, 2022 $ 450 $ — Pool participation (a) 13,073 (a) 138 (b) $ 13,523 (c) $ 138 Property damage: NEIL and EMANI April 1, 2021 $ 3,200 (d) $ 25 (e) Accidental outage: NEIL April 1, 2021 $ 490 (f) $ 7 (e) (a) Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program. (b) Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year. (c) Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors. (d) NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events. (e) All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL. (f) Accidental outage insurance provides for lost sales in the event of a prolonged accidental outage. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Nonradiation events are limited to $328 million. The Price-Anderson Act is a federal law that limits the liability for claims from an incident involving any licensed United States commercial nuclear energy center. The limit is based on the number of licensed reactors. The limit of liability and the maximum potential annual payments are adjusted at least every five years for inflation to reflect changes in the Consumer Price Index. The most recent five-year inflationary adjustment became effective in November 2018. Owners of a nuclear reactor cover this exposure through a combination of private insurance and mandatory participation in a financial protection pool, as established by the Price-Anderson Act.

Retirement Benefits

Retirement Benefits	12 Months Ended
	Dec. 31, 2021
Retirement Benefits [Abstract]
RETIREMENT BENEFITS	RETIREMENT BENEFITS The primary objective of the Ameren pension and postretirement benefit plans is to provide eligible employees with pension and postretirement health care and life insurance benefits. Ameren has defined benefit pension plans covering substantially all of its employees and has a postretirement benefit plan covering non-union employees hired before October 2015 and union employees hired before January 2020. Ameren Missouri and Ameren Illinois each participate in Ameren’s single-employer pension and other postretirement plans. All non-union employees participate in a cash balance pension plan. Ameren Missouri union employees hired after June 2013, and Ameren Illinois union employees hired after mid-October 2012, participate in a cash balance pension plan. Ameren uses a measurement date of December 31 for its pension and postretirement benefit plans. Ameren’s qualified pension plan is the Ameren Retirement Plan. Ameren’s other postretirement plan is the Ameren Retiree Welfare Benefit Plan. Ameren also has an unfunded nonqualified pension plan, the Ameren Supplemental Retirement Plan, which is available to provide certain management employees and retirees with a supplemental benefit when their qualified pension plan benefits are capped in compliance with Internal Revenue Code limitations. Only Ameren subsidiaries participate in the plans listed above. Ameren’s pension and other postretirement benefit plans were overfunded by $717 million and $249 million in the aggregate as of December 31, 2021 and 2020, respectively. These net assets are recorded in “Pension and other postretirement benefits,” “Other current liabilities,” and “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. The increase in the overfunded pension and postretirement benefit plans during 2021 was primarily the result of an increase in the return on plan assets of the pension and postretirement trusts and a 25 basis point increase in the pension and other postretirement benefit plan discount rates used to determine the present value of the obligation. The overfunded pension and other postretirement benefit plans also resulted in regulatory liabilities on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets. The following table presents the net benefit liability/(asset) recorded on the balance sheets as of December 31, 2021 and 2020: 2021 2020 Ameren (a) $ (717) $ (249) Ameren Missouri (a) (189) (25) Ameren Illinois (a) (416) (210) (a) Liabilities associated with pension and other postretirement benefits are recorded in “Other current liabilities” and “Other deferred credits and liabilities” on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets. Ameren recognizes the overfunded and underfunded status of its pension and postretirement plans as an asset or a liability on its consolidated balance sheet, with offsetting entries to accumulated OCI and regulatory assets or liabilities. The following table presents the funded status of Ameren’s pension and postretirement benefit plans as of December 31, 2021 and December 31, 2020. It also provides the amounts included in regulatory assets or liabilities and accumulated OCI at December 31, 2021 and December 31, 2020, that have not been recognized in net periodic benefit costs. 2021 2020 Pension Postretirement Pension Postretirement Accumulated benefit obligation at end of year $ 5,174 $ (a) $ 5,213 $ (a) Change in benefit obligation: Net benefit obligation at beginning of year $ 5,510 $ 1,204 $ 4,967 $ 1,110 Service cost 134 23 110 19 Interest cost 152 33 174 39 Participant contributions — 9 — 8 Actuarial (gain) loss (82) (80) 508 91 Benefits paid (257) (60) (249) (63) Net benefit obligation at end of year 5,457 1,129 5,510 1,204 Change in plan assets: Fair value of plan assets at beginning of year 5,510 1,453 4,564 1,297 Actual return on plan assets 432 154 1,143 209 Employer contributions 60 2 52 2 Participant contributions — 9 — 8 Benefits paid (257) (60) (249) (63) Fair value of plan assets at end of year 5,745 1,558 5,510 1,453 Funded status – surplus (288) (429) — (249) Accrued benefit asset at December 31 $ (288) $ (429) $ — $ (249) Amounts recognized in the balance sheet consist of: Noncurrent asset $ (327) $ (429) $ (39) $ (249) Current liability (b) 2 — 2 — Noncurrent liability (c) 37 — 37 — Net asset recognized $ (288) $ (429) $ — $ (249) Amounts recognized in regulatory assets or liabilities consist of: Net actuarial gain $ (415) $ (343) $ (138) $ (200) Prior service credit — (33) — (37) Amounts recognized in accumulated OCI (pretax) consist of: Net actuarial (gain) loss (8) 1 5 6 Total $ (423) $ (375) $ (133) $ (231) (a) Not applicable. (b) Included in “Other current liabilities” on Ameren’s consolidated balance sheet. (c) Included in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. The following table presents the assumptions used to determine our benefit obligations at December 31, 2021 and 2020: Pension Benefits Postretirement Benefits 2021 2020 2021 2020 Discount rate at measurement date 3.00 % 2.75 % 3.00 % 2.75 % Increase in future compensation 3.50 3.50 3.50 3.50 Cash balance pension plan interest crediting rate 5.00 5.00 (a) (a) Medical cost trend rate (initial) (b) (a) (a) 5.00 5.00 Medical cost trend rate (ultimate) (b) (a) (a) 5.00 5.00 (a) Not applicable. (b) Initial and ultimate medical cost trend rate for certain Medicare-eligible participants was 2.50% and 3.00% at December 31, 2021 and 2020, respectively. Ameren determines discount rate assumptions by identifying a theoretical settlement portfolio of high-quality corporate bonds sufficient to provide for a plan’s projected benefit payments. The settlement portfolio of bonds is selected from a pool of approximately 820 high-quality corporate bonds. A single discount rate is then determined; that rate results in a discounted value of the plan’s benefit payments that equates to the market value of the selected bonds. During 2021, Ameren elected to continue to use the Society of Actuaries mortality table and the Society of Actuaries 2020 Mortality Improvement Scale. Funding Pension benefits are based on the employees’ years of service, age, and compensation. Ameren’s pension plans are funded in compliance with income tax regulations, federal funding requirements, and other regulatory requirements. As a result, Ameren expects to fund its pension plans at a level equal to the greater of the pension cost or the legally required minimum contribution. Based on its assumptions at December 31, 2021, its investment performance in 2021, and its pension funding policy, Ameren, Ameren Missouri, and Ameren Illinois do not expect to make material contributions in the aggregate over the next five years. These estimated contributions may change based on actual investment performance, changes in interest rates, changes in our assumptions, changes in government regulations, and any voluntary contributions. Our funding policy for postretirement benefits is primarily to fund the Voluntary Employee Beneficiary Association (VEBA) trusts to match the annual postretirement expense. The following table presents the cash contributions made to our defined benefit retirement plans and to our postretirement plan during 2021, 2020, and 2019: Pension Benefits Postretirement Benefits 2021 2020 2019 2021 2020 2019 Ameren Missouri $ 22 $ 17 $ 3 $ 1 $ 1 $ 1 Ameren Illinois 28 27 19 1 1 1 Ameren Services 10 8 1 — — 1 Ameren $ 60 $ 52 $ 23 $ 2 $ 2 $ 3 Investment Strategy and Policies Ameren manages plan assets in accordance with the “prudent investor” guidelines contained in ERISA. The investment committee, which includes members of senior management, approves and implements investment strategy and asset allocation guidelines for the plan assets. The investment committee’s goals are twofold: first, to ensure that sufficient funds are available to provide the benefits at the time they are payable; and second, to maximize total return on plan assets and to minimize expense volatility consistent with its tolerance for risk. Ameren delegates the task of investment management to specialists in each asset class. As appropriate, Ameren provides each investment manager with guidelines that specify allowable and prohibited investment types. The investment committee regularly monitors manager performance and compliance with investment guidelines. The expected return on plan assets assumption is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Projected rates of return for each asset class were estimated after an analysis of historical experience, future expectations, and the volatility of the various asset classes. After considering the target asset allocation for each asset class, we reviewed the overall expected rate of return for the portfolio for historical and expected experience of active portfolio management results compared with benchmark returns and for the effect of expenses paid from plan assets. Ameren will use an expected return on plan assets for its pension and postretirement plan assets of 6.50% in 2022. Ameren’s investment committee strives to assemble a portfolio of diversified assets that does not create a significant concentration of risks. The investment committee develops asset allocation guidelines between asset classes, and it creates diversification through investments in assets that differ by type (equity, debt, real estate), duration, market capitalization, country, style (growth or value), and industry, among other factors. The diversification of assets is displayed in the target allocation table below. The investment committee also routinely rebalances the plan assets to adhere to the diversification goals. The investment committee’s strategy reduces the concentration of investment risk; however, Ameren is still subject to overall market risk. Effective January 2020, Ameren’s investment committee developed and implemented a liability hedging investment strategy for its qualified pension plans designed to reduce interest rate risk as part of an objective for its long-term investment strategy. The plan invests in derivative instruments mainly consisting of interest rate futures intended to extend the duration of the pension plan assets so that the assets are more closely aligned with the duration of the liabilities. In addition, part of Ameren’s investment strategy includes participation in a securities lending program, which allows it to lend eligible securities to third party borrowers. All loans are collateralized by at least 102% of the loaned asset’s market value and the collateral is invested in the form of cash, government obligations, and U.S. agency obligations. Ameren’s fair value of securities loaned was $374 million and $365 million as of December 31, 2021 and 2020, respectively. Cash and securities obtained as collateral exceeded the fair value of the securities loaned as of December 31, 2021 and 2020. The following table presents our target allocations and our pension and postretirement plans’ asset categories as of December 31, 2021 and 2020: Asset Target Allocation 2021 (a) Percentage of Plan Assets at December 31, 2021 2020 Pension Plan: Cash and cash equivalents 0% – 5% 3 % 1 % Equity securities: U.S. large-capitalization 11% – 21% 23 % 26 % U.S. small- and mid-capitalization 3% – 13% 9 % 9 % International 9% – 19% 15 % 15 % Global 7% – 17% 11 % 9 % Total equity 45% – 55% 58 % 59 % Debt securities 35% – 45% 35 % 36 % Real estate 0% – 10% 4 % 4 % Private equity 0% – 5% (b) (b) Diversified credit 0% – 10% (b) (b) Total 100 % 100 % Postretirement Plans: Cash and cash equivalents 0% – 7% 3 % 3 % Equity securities: U.S. large-capitalization 23% – 33% 30 % 31 % U.S. small- and mid-capitalization 3% – 13% 9 % 8 % International 9% – 19% 13 % 15 % Global 5% – 15% 10 % 10 % Total equity 55% – 65% 62 % 64 % Debt securities 33% – 43% 35 % 33 % Total 100 % 100 % (a) These target allocations reflect targets that were approved in 2021 to take effect in the subsequent year. (b) Less than 1% of plan assets. In general, the United States large-capitalization equity investments are passively managed or indexed, whereas the international, global, United States small-capitalization, and United States mid-capitalization equity investments are actively managed by investment managers. Debt securities include a broad range of fixed-income vehicles. Debt security investments in high-yield securities and non-United-States-dollar-denominated securities are owned by the plans, but in limited quantities to reduce risk. Most of the debt security investments are under active management by investment managers. Real estate investments include private real estate vehicles; however, Ameren does not, by policy, hold direct investments in real estate property. In addition to the derivative investments included in the liability hedging investment strategy described above, Ameren’s investment committee also allo ws investment managers to use derivatives, such as index futures, foreign exchange futures, and options, in certain situations to increase or to reduce market exposure in an efficient and timely manner. Fair Value Measurements of Plan Assets Investments in the pension and postretirement benefit plans were stated at fair value as of December 31, 2021. Fair value is defined as the price that would be received for an asset in the principal or most advantageous market for the asset in an orderly transaction between market participants on the measurement date. Cash and cash equivalents have initial maturities of three months or less and are recorded at cost plus accrued interest. Investments traded in active markets on national or international securities exchanges are valued at closing prices on the measurement date or, if that is not a business day, on the last business day before that date. Securities traded in over-the-counter markets are valued by quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Investments measured under NAV as a practical expedient are based on the fair values of the underlying assets provided by the funds and their administrators. The fair value of real estate investments is based on NAV; it is determined by annual appraisal reports prepared by an independent real estate appraiser. Investments measured at NAV often provide for daily, monthly, or quarterly redemptions with 60 or less days of notice depending on the fund. For some funds, redemption may also require approval from the fund’s board of directors. Derivative contracts are valued at fair value, as determined by the investment managers (or independent third parties on behalf of the investment managers), who use proprietary models and take into consideration exchange quotations on underlying instruments, dealer quotations, and other market information. The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plans’ assets measured at fair value and NAV as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Level 1 Level 2 NAV Total Level 1 Level 2 NAV Total Cash and cash equivalents $ — $ — $ 116 $ 116 $ — $ — $ 145 $ 145 Equity securities: U.S. large-capitalization — — 1,381 1,381 — — 1,511 1,511 U.S. small- and mid-capitalization 558 — — 558 513 — — 513 International 372 — 531 903 375 — 492 867 Global — — 621 621 — — 546 546 Debt securities: Corporate bonds — 545 27 572 — 506 17 523 Municipal bonds — 50 — 50 — 50 — 50 U.S. Treasury and agency securities — 1,450 — 1,450 3 1,325 — 1,328 Other 17 11 — 28 (5) 8 — 3 Real estate — — 228 228 — — 208 208 Private equity — — 1 1 — — 2 2 Total $ 947 $ 2,056 $ 2,905 $ 5,908 $ 886 $ 1,889 $ 2,921 $ 5,696 Less: Medical benefit assets (a) (234) (219) Plus: Net receivables (b) 71 33 Fair value of pension plans’ assets $ 5,745 $ 5,510 (a) Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. (b) Receivables related to pending securities sales, offset by payables related to pending securities purchases. The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans’ assets measured at fair value and NAV as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Level 1 Level 2 NAV Total Level 1 Level 2 NAV Total Cash and cash equivalents $ 24 $ — $ — $ 24 $ 38 $ — $ — $ 38 Equity securities: U.S. large-capitalization 283 — 115 398 279 — 107 386 U.S. small- and mid-capitalization 113 — — 113 104 — — 104 International 60 — 117 177 75 — 107 182 Global — — 132 132 — — 120 120 Debt securities: Municipal bonds — 133 — 133 — 106 — 106 Other — — 335 335 — — 295 295 Total $ 480 $ 133 $ 699 $ 1,312 $ 496 $ 106 $ 629 $ 1,231 Plus: Medical benefit assets (a) 234 219 Plus: Net receivables (b) 12 3 Fair value of postretirement benefit plans’ assets $ 1,558 $ 1,453 (a) Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above. (b) Receivables related to pending securities sales, offset by payables related to pending securities purchases. Net Periodic Benefit Cost The following table presents the components of the net periodic benefit cost of Ameren’s pension and postretirement benefit plans during 2021, 2020, and 2019: Pension Benefits Postretirement Benefits 2021 2020 2019 2021 2020 2019 Service cost (a) $ 134 $ 110 $ 88 $ 23 $ 19 $ 18 Non-service cost components: Interest cost 152 174 187 33 39 43 Expected return on plan assets (297) (291) (276) (80) (80) (77) Amortization of: Prior service credit — (1) (1) (4) (4) (5) Actuarial (gain) loss 73 60 25 (6) (9) (15) Total non-service cost components (b) $ (72) $ (58) $ (65) $ (57) $ (54) $ (54) Net periodic benefit cost (income) $ 62 $ 52 $ 23 $ (34) $ (35) $ (36) (a) Service cost, net of capitalization, is reflected in “Operating Expenses - Other operations and maintenance” on Ameren’s statement of income. (b) Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 6 – Other Income, Net for additional information. The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred for the years ended December 31, 2021, 2020, and 2019: Pension Costs Postretirement Costs 2021 2020 2019 2021 2020 2019 Ameren Missouri (a) $ 29 $ 22 $ 5 $ (4) $ (5) $ (6) Ameren Illinois 34 32 20 (31) (31) (30) Other (1) (2) (2) 1 1 — Ameren $ 62 $ 52 $ 23 $ (34) $ (35) $ (36) (a) Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri and the level of such costs included in customer rates. The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2021, are as follows: Pension Benefits Postretirement Benefits Paid from Paid from Paid from Paid from 2022 $ 267 $ 2 $ 59 $ 2 2023 274 2 60 2 2024 279 3 61 2 2025 284 3 61 2 2026 288 3 60 2 2027 – 2031 1,476 12 296 9 The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2021, 2020, and 2019: Pension Benefits Postretirement Benefits 2021 2020 2019 2021 2020 2019 Discount rate at measurement date 2.75 % 3.50 % 4.25 % 2.75 % 3.50 % 4.25 % Expected return on plan assets 6.50 7.00 7.00 6.50 7.00 7.00 Increase in future compensation 3.50 3.50 3.50 3.50 3.50 3.50 Cash balance pension plan interest crediting rate 5.00 5.00 5.00 (a) (a) (a) Medical cost trend rate (initial) (b) (a) (a) (a) 5.00 5.00 5.00 Medical cost trend rate (ultimate) (b) (a) (a) (a) 5.00 5.00 5.00 (a) Not applicable. (b) Initial and ultimate medical cost trend rate for certain Medicare-eligible participants is 3.00%. Other Ameren sponsors a 401(k) plan for eligible employees. The Ameren 401(k) plan covered all eligible Ameren employees at December 31, 2021. The plan allows employees to contribute a portion of their compensation in accordance with specific guidelines. Ameren matches a percentage of the employee contributions up to certain limits. The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to each of the Ameren Companies for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri $ 21 $ 20 $ 19 Ameren Illinois 16 17 16 Other 1 1 — Ameren $ 38 $ 38 $ 35

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The 2014 Omnibus Incentive Compensation Plan is Ameren’s long-term stock-based compensation plan for eligible employees and directors. It provides for a maximum of 8 million common shares to be available for grant to eligible employees and directors. At December 31, 2021, there were 1.8 million common shares remaining for grant. Awards may be stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance share units, cash-based awards, and other stock-based awards. Ameren used newly issued shares to fulfill its stock-based compensation obligations for 2021, 2020, and 2019, and intends to use newly issued shares to fulfill its stock-based compensation obligations for 2022. The following table summarizes Ameren’s nonvested performance share unit and restricted stock unit activity for the year ended December 31, 2021: Performance Share Units – Market Condition (a) Performance Share Units – Performance Condition (b) Restricted Stock Units Share Weighted-average Fair Value per Share Unit Shares Weighted-average Fair Value per Share Unit Stock Weighted-average Fair Value per Stock Unit Nonvested at January 1, 2021 (c) 464,139 $ 73.34 31,896 $ 76.66 303,695 $ 68.52 Granted 266,081 87.11 42,672 78.11 129,723 78.17 Forfeitures (21,143) 80.77 (2,449) 77.55 (10,209) 74.88 Vested and undistributed (d) (186,792) 77.91 (15,134) 77.27 (87,427) 73.13 Vested and distributed (93,499) 62.88 — — (87,597) 56.38 Performance share adjustment — — (13,881) 77.54 — — Nonvested at December 31, 2021 (e) 428,786 $ 81.81 43,104 $ 77.54 248,185 $ 75.97 (a) The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions. Compensation cost on nonforfeited awards is recognized regardless of whether Ameren achieves the specified market conditions. (b) The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. Compensation cost is recognized ratably over the requisite service period only for awards for which it is probable that the performance condition will be satisfied. The performance share adjustment represents the change in the probability that a performance condition will be satisfied. (c) Does not include 366,243 market condition performance share units, 7,607 performance shares based on Ameren’s clean energy transition, and 160,034 restricted stock units that were vested and undistributed. (d) Vested and undistributed units are awards that vest on a pro-rata basis due to attainment of retirement eligibility by certain employees, but have not yet been distributed. For vested and undistributed performance share units, the number of shares issued for retirement-eligible employees will vary depending on actual performance over the three-year performance period. (e) Does not include 357,575 market condition performance share units, 22,739 performance shares based on Ameren’s clean energy transition, and 164,000 restricted stock units that were vested and undistributed. Performance Share Units – Market Condition A market condition performance share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, certain specified market conditions have been met and if the individual remains employed by Ameren through the required vesting period. The vesting period for share units awarded extends beyond the three-year performance period to the payout date, which is approximately 38 months after the grant date. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis over the three-year performance period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions. The fair value of each share unit is based on Ameren’s closing common share price at December 31 of the year prior to the award year and a Monte Carlo simulation. The Monte Carlo simulation is used to estimate expected share payout based on Ameren’s TSR for a three-year performance period relative to the designated peer group beginning January 1st of the award year. The simulation can produce a greater fair value for the share unit than the applicable closing common share price because it includes the weighted payout scenarios in which an increase in the share price has occurred and/or in which the payout is above 100% due to Ameren’s projected TSR performance. The significant assumptions used to calculate fair value also include a three-year risk-free rate, Ameren’s common stock volatility, and volatility for the peer group. The following table presents the fair value of each share unit along with the significant assumptions used to calculate the fair value of each share unit for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Fair value of share units awarded $87.11 $82.49 $67.42 Three-year risk-free rate 0.17% 1.62% 2.46% Ameren’s common stock volatility (a) 28% 15% 17% Volatility range for the peer group (a) 26% – 36% 14% – 28% 15% – 25% (a) Based on a historical period that is equal to the remaining term of the performance period as of the grant date. Performance Share Units – Performance Condition A performance condition share unit vests and entitles an employee to receive shares of Ameren common stock (plus accumulated dividends) if, at the end of the three-year performance period, Ameren has met the specified performance condition and if the individual remains employed by Ameren through the required vesting period. The vesting period for share units awarded extends beyond the three-year performance period to the payout date, which is approximately 38 months after the grant date. In the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis over the three-year performance period. The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual performance conditions achieved. The specified performance condition is based on Ameren’s clean energy transition. The grant-date fair value for an individual outcome of a performance condition is determined by Ameren’s closing common share price on the grant date. Restricted Stock Units Restricted stock units vest and entitle an employee to receive shares of Ameren common stock (plus accumulated dividends) if the individual remains employed with Ameren through the payment date of the awards. Generally, in the event of a participant’s death or retirement at age 55 or older with five years or more of service, awards vest on a pro-rata basis. The payout date of the awards is approximately 38 months after the grant date. The fair value of each restricted stock unit is determined by Ameren’s closing common share price on the grant date. Stock-Based Compensation Expense The following table presents the stock-based compensation expense for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri $ 5 $ 5 $ 4 Ameren Illinois 3 3 3 Other (a) 14 13 13 Ameren 22 21 20 Less: Income tax benefit 6 6 5 Stock-based compensation expense, net $ 16 $ 15 $ 15 (a) Represents compensation expense for employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above. Ameren settled performance share units and restricted stock units of $50 million, $58 million, and $83 million for the years ended December 31, 2021, 2020, and 2019. There were no significant stock-based compensation costs capitalized during the years ended December 31, 2021, 2020, and 2019. As of December 31, 2021, total compensation cost of $35 million related to nonvested awards not yet recognized is expected to be recognized over a weighted-average period of 21 months. For the years ended December 31, 2021, 2020, and 2019, excess tax benefits associated with the settlement of stock-based compensation awards reduced income tax expense by $5 million, $8 million, and $15 million, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Missouri Income Tax Rate In 2018, legislation modifying Missouri tax law was enacted to decrease the state’s corporate income tax rate from 6.25% to 4%, effective January 1, 2020. As a result, in 2018, Ameren’s and Ameren Missouri’s accumulated deferred tax balances were revalued, resulting in a net decrease of $122 million to their accumulated deferred tax liability, which was offset by a regulatory liability. Additionally, Ameren recorded an immaterial amount to income tax expense. As a result of the March 2020 MoPSC electric rate order, the effect of this tax decrease was reflected in customer rates on April 1, 2020. This income tax decrease did not have a material impact on the net income of Ameren (parent) and nonregistrant subsidiaries. The following table presents the principal reasons for the difference between the effective income tax rate and the federal statutory corporate income tax rate for the years ended December 31, 2021, 2020, and 2019: Ameren Missouri Ameren Illinois Ameren 2021 Federal statutory corporate income tax rate 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred income taxes (15) (3) (8) Amortization of deferred investment tax credit (1) — — Renewable and other tax credits (7) (a) — (3) (a) State tax 3 7 5 Stock-based compensation — — (1) Effective income tax rate 1 % 25 % 14 % 2020 Federal statutory corporate income tax rate 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred income taxes (16) (3) (9) Amortization of deferred investment tax credit (1) (1) (1) State tax 3 7 5 Stock-based compensation — — (1) Effective income tax rate 7 % 24 % 15 % 2019 Federal statutory corporate income tax rate 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred income taxes (11) (4) (7) Amortization of deferred investment tax credit (1) — (1) State tax 5 7 6 Stock-based compensation — — (1) Effective income tax rate 14 % 24 % 18 % (a) Includes credits associated with the High Prairie Renewable and Atchison Renewable energy centers. Ameren Missouri placed the High Prairie Renewable Energy Center in service in December 2020. Additionally, Ameren Missouri placed in service the wind turbines at its Atchison Renewable Energy Center throughout the first half of 2021. The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The following table presents the components of income tax expense (benefit) for the years ended December 31, 2021, 2020, and 2019: Ameren Missouri Ameren Illinois Other Ameren 2021 Current taxes: Federal $ — $ (15) $ 22 $ 7 State — (7) 1 (6) Deferred taxes: Federal 65 120 (15) 170 State 23 59 4 86 Amortization of excess deferred income taxes (81) (14) (1) (96) Amortization of deferred investment tax credits (4) — — (4) Total income tax expense $ 3 $ 143 $ 11 $ 157 2020 Current taxes: Federal $ 14 $ 12 $ (24) $ 2 State 3 (6) 8 5 Deferred taxes: Federal 82 81 24 187 State 15 52 (10) 57 Amortization of excess deferred income taxes (75) (15) (1) (91) Amortization of deferred investment tax credits (5) — — (5) Total income tax expense (benefit) $ 34 $ 124 $ (3) $ 155 2019 Current taxes: Federal $ 65 $ 19 $ (88) $ (4) State 22 11 (14) 19 Deferred taxes: Federal 37 66 82 185 State 5 29 25 59 Amortization of excess deferred income taxes (56) (15) (1) (72) Amortization of deferred investment tax credits (5) — — (5) Total income tax expense $ 68 $ 110 $ 4 $ 182 The following table presents the accumulated deferred income tax assets and liabilities recorded as a result of temporary differences and accumulated deferred investment tax credits at December 31, 2021 and 2020: Ameren Missouri Ameren Illinois Other Ameren 2021 Accumulated deferred income taxes, net liability (asset): Plant-related $ 2,188 $ 1,715 $ 226 $ 4,129 Regulatory assets and liabilities, net (259) (199) (25) (483) Deferred employee benefit costs (52) 17 (53) (88) Tax carryforwards (68) (46) (84) (198) Other 13 71 25 109 Total net accumulated deferred income tax liabilities (assets) 1,822 1,558 89 3,469 Accumulated deferred investment tax credits 30 — — 30 Accumulated deferred income taxes and investment tax credits $ 1,852 $ 1,558 $ 89 $ 3,499 2020 Accumulated deferred income taxes, net liability (asset): Plant-related $ 2,112 $ 1,559 $ 205 $ 3,876 Regulatory assets and liabilities, net (285) (207) (23) (515) Deferred employee benefit costs (58) 8 (54) (104) Tax carryforwards (26) (6) (65) (97) Other (35) 13 39 17 Total net accumulated deferred income tax liabilities (assets) 1,708 1,367 102 3,177 Accumulated deferred investment tax credits 34 — — 34 Accumulated deferred income taxes and investment tax credits $ 1,742 $ 1,367 $ 102 $ 3,211 The following table presents the components of accumulated deferred income tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2021 and 2020: Ameren Missouri Ameren Illinois Other Ameren 2021 Net operating loss carryforwards: Federal (a) $ 2 $ 17 $ 15 $ 34 State (b) $ 1 $ 25 $ 5 $ 31 Total net operating loss carryforwards $ 3 $ 42 $ 20 $ 65 Tax credit carryforwards: Federal (c) $ 65 $ 3 $ 58 $ 126 State (d) — 1 6 7 Total tax credit carryforwards $ 65 $ 4 $ 64 $ 133 2020 Net operating loss carryforwards: State $ — $ 3 $ 4 $ 7 Total net operating loss carryforwards $ — $ 3 $ 4 $ 7 Tax credit carryforwards: Federal $ 26 $ 3 $ 54 $ 83 State — — 7 7 Total tax credit carryforwards $ 26 $ 3 $ 61 $ 90 (a) Will not expire. (b) Will expire between 2032 and 2041. (c) Will expire between 2030 and 2041. (d) Will expire between 2022 and 2026. Uncertain Tax Positions As of December 31, 2021 and 2020, the Ameren Companies did not record any uncertain tax positions. Ameren is a part of the IRS’s compliance assurance process program, which involves real-time review of compliance with federal income tax law. State income tax returns are generally subject to examination for a period of three years after filing. The state impact of any federal changes remains subject to examination by various states for up to one year after formal notification to the states. Ameren’s federal tax returns for the 2015, 2017, 2018, 2019, and 2020 tax years are open, but, at the time of this filing, the Ameren Companies do not have material income tax issues under examination, administrative appeals, or litigation. Ameren Missouri has an uncertain tax position tracker. Under Missouri’s regulatory framework, uncertain tax positions do not reduce Ameren Missouri’s electric rate base. When an uncertain income tax position liability is resolved, the MoPSC requires, through the uncertain tax position tracker, the creation of a regulatory asset or regulatory liability to reflect the time value, with a return at the applicable WACC included in each of the electric rate orders in effect before the tax position was resolved, of the difference between the uncertain tax position liability that was excluded from rate base and the final tax liability. The resulting regulatory asset or liability will affect earnings in the year it is created. It will then be amortized over three years, beginning on the effective date of new rates established in the next electric service regulatory rate review.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED-PARTY TRANSACTIONS In the normal course of business, Ameren Missouri and Ameren Illinois engage in affiliate transactions. These transactions primarily consist of natural gas and power purchases and sales, services received or rendered, and borrowings and lendings. Transactions between Ameren’s subsidiaries are reported as affiliate transactions on their individual financial statements, but those transactions are eliminated in consolidation for Ameren’s consolidated financial statements, except as noted in Software Licensing Agreement discussion below. Below are the material related-party agreements. Electric Power Supply Agreements Ameren Illinois must acquire capacity and energy sufficient to meet its obligations to customers. Ameren Illinois uses periodic RFP processes, administered by the IPA and approved by the ICC, to contract capacity and energy on behalf of its customers. Ameren Missouri participates in the RFP process and has been a winning supplier for certain periods. Capacity Supply Agreements In procurement events in 2021, Ameren Missouri contracted to supply a portion of Ameren Illinois’ capacity requirements for $2 million from June 2022 through May 2023. Energy Product Agreements Based on the outcome of IPA-administered procurement events, Ameren Missouri and Ameren Illinois have entered into energy product agreements by which Ameren Missouri agreed to sell, and Ameren Illinois agreed to purchase, a set amount of MWhs at a predetermined price over a specified period of time. The following table presents the specified performance period, price, and amount of MWhs included in the agreements: IPA Procurement Event Performance Period MWh Average Price per MWh April 2017 March 2019 – May 2020 85,600 $ 34 April 2018 June 2019 – September 2020 110,000 32 April 2019 January 2020 – December 2021 288,000 35 September 2019 April 2020 – November 2021 170,800 29 September 2020 September 2021 – November 2022 204,800 31 April 2021 July 2022 – November 2022 33,600 34 September 2021 January 2022 – September 2023 136,000 37 Collateral Postings Under the terms of the Illinois energy product agreements entered into through RFP processes administered by the IPA, suppliers must post collateral under certain market conditions to protect Ameren Illinois in the event of nonperformance. The collateral postings are unilateral, which means that only the suppliers can be required to post collateral. Therefore, Ameren Missouri, as a winning supplier in the RFP process, may be required to post collateral. As of December 31, 2021 and 2020, there were no collateral postings required of Ameren Missouri related to the Illinois energy product agreements. Interconnection Agreements Ameren Missouri and Ameren Illinois are parties to an interconnection agreement that governs the connection of their respective transmission lines and other facilities used for the distribution of power. These agreements have no contractual expiration date, but may be terminated by either party with three years’ notice. Ameren Missouri and ATXI are parties to an interconnection agreement that governs the connection of the High Prairie Renewable Energy Center to an ATXI transmission line that allows Ameren Missouri to distribute power generated from the High Prairie Renewable Energy Center. See Note 15 – Supplemental Information for further information on the acquisition of the High Prairie Renewable Energy Center. Support Services Agreements Ameren Services provides support services to its affiliates. The costs of support services including wages, employee benefits, professional services, and other expenses, are based on, or are an allocation of, actual costs incurred. The support services agreement can be terminated at any time by the mutual agreement of Ameren Services and that affiliate or by either party with 60 days’ notice before the end of a calendar year. In addition, Ameren Missouri and Ameren Illinois provide affiliates with access to their facilities for administrative purposes and with use of other assets. The costs of the rent and facility services and other assets are based on, or are an allocation of, actual costs incurred. Ameren Missouri and Ameren Illinois also provide storm-related and miscellaneous support services to each other on an as-needed basis. At December 31, 2021, Ameren Missouri and Ameren Illinois had long-term receivables included in “Other assets” from Ameren Services of $77 million and $80 million, respectively, related to Ameren Services’ allocated portion of Ameren’s pension and postretirement benefit plans. Transmission Services Ameren Missouri and Ameren Illinois receives transmission services from ATXI for their retail load. Electric Transmission Maintenance and Construction Agreements ATXI entered into separate agreements with Ameren Missouri and Ameren Illinois in which Ameren Missouri or Ameren Illinois, as applicable, may perform certain maintenance and construction services related to ATXI’s electric transmission assets. Money Pool See Note 4 – Short-term Debt and Liquidity for a discussion of affiliate borrowing arrangements. Software Licensing Agreement In September 2019, Ameren Missouri purchased a license for advanced metering infrastructure software from Ameren Illinois. The amount of the $24 million cost-based transaction price over the $5 million remaining carrying value of the software was recorded as revenue by Ameren Illinois, with $14 million of revenue recorded at Ameren Illinois Electric Distribution and $5 million recorded at Ameren Illinois Natural Gas. The revenue recorded at Ameren Illinois Electric Distribution was reflected in formula ratemaking, which resulted in no impact to net income. Per authoritative accounting guidance for sales to rate-regulated entities, the revenue recognized by Ameren Illinois was not eliminated upon consolidation by Ameren. Ameren Missouri’s cost-based investment of $24 million was included in “Property, Plant, and Equipment, Net.” Tax Allocation Agreement See Note 1 – Summary of Significant Accounting Policies for a discussion of the tax allocation agreement. The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of December 31, 2021 and December 31, 2020: 2021 2020 Ameren Missouri Ameren Illinois Ameren Missouri Ameren Illinois Income taxes payable to parent (a) $ — $ 8 $ — $ 6 Income taxes receivable from parent (b) 27 18 9 15 (a) Included in “Accounts payable – affiliates” on the balance sheet. (b) Included in “Accounts receivable – affiliates” on the balance sheet. Capital Contributions The following table presents cash capital contributions received from Ameren (parent) by Ameren Missouri and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri (a) $ 207 $ 491 $ 124 Ameren Illinois (a) 262 464 15 (a) Includes capital contributions made as a result of the tax allocation agreement. Effects of Related-party Transactions on the Statement of Income The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the years ended December 31, 2021, 2020, and 2019. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity. Agreement Income Statement Line Item Ameren Ameren Ameren Missouri power supply agreements Operating Revenues 2021 $ 16 $ (a) with Ameren Illinois 2020 11 (a) 2019 3 (a) Ameren Missouri and Ameren Illinois Operating Revenues 2021 26 1 rent and facility services 2020 26 1 2019 27 2 Ameren Missouri and Ameren Illinois miscellaneous Operating Revenues 2021 (b) 5 support services and services provided to ATXI 2020 3 1 2019 1 2 Ameren Missouri software licensing Operating Revenues 2021 (a) (a) with Ameren Illinois 2020 (a) (a) 2019 (a) 19 Total Operating Revenues 2021 $ 42 $ 6 2020 40 2 2019 31 23 Ameren Illinois power supply Purchased Power 2021 $ (a) $ 16 agreements with Ameren Missouri 2020 (a) 11 2019 (a) 3 Ameren Missouri and Ameren Illinois Purchased Power 2021 4 1 transmission services from ATXI 2020 (a) 2 2019 (a) 2 Total Purchased Power 2021 $ 4 $ 17 2020 (a) 13 2019 (a) 5 Ameren Missouri and Ameren Illinois Other Operations and 2021 $ 1 $ 4 rent and facility services Maintenance 2020 (b) 4 2019 2 5 Ameren Services support services Other Operations and 2021 147 137 agreement Maintenance 2020 140 133 2019 135 127 Total Other Operations and 2021 $ 148 $ 141 Maintenance Expenses 2020 140 137 2019 137 132 Money pool borrowings (advances) (Interest Charges) 2021 $ (b) $ (b) Other Income, Net 2020 (b) (b) 2019 (b) (b) (a) Not applicable. (b) Amount less than $1 million.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES We are involved in legal, tax, and regulatory proceedings before various courts, regulatory commissions, authorities, and governmental agencies with respect to matters that arise in the ordinary course of business, some of which involve substantial amounts of money. We believe that the final disposition of these proceedings, except as otherwise disclosed in the notes to our financial statements, will not have a material adverse effect on our results of operations, financial position, or liquidity. See also Note 1 – Summary of Significant Accounting Policies, Note 2 – Rate and Regulatory Matters, Note 9 – Callaway Energy Center, Note 13 – Related-party Transactions, and Note 15 – Supplemental Information in this report. Environmental Matters Our electric generation, transmission, and distribution and natural gas distribution and storage operations must comply with a variety of statutes and regulations relating to the protection of the environment and human health and safety including permitting programs implemented via federal, state, and local authorities. Such environmental laws address air emissions; discharges to water bodies; the storage, handling and disposal of hazardous substances and waste materials; siting and land use requirements; and potential ecological impacts. Complex and lengthy processes are required to obtain and renew approvals, permits, and licenses for new, existing, or modified facilities. Additionally, the use and handling of various chemicals or hazardous materials require release prevention plans and emergency response procedures. We employ dedicated personnel knowledgeable in environmental matters to oversee our business activities’ compliance with regulatory requirements. Environmental regulations have a significant impact on the electric utility industry and compliance with these regulations could be costly for Ameren Missouri, which operates coal-fired power plants. Clean Air Act regulations that apply to the electric utility industry include the NSPS, the CSAPR, the MATS, and the National Ambient Air Quality Standards, which are subject to periodic review for certain pollutants. Collectively, these regulations cover a variety of pollutants, such as SO 2 , particulate matter, NO x , mercury, toxic metals, and acid gases, and CO 2 emissions from new power plants. Regulations implementing the Clean Water Act govern both intake and discharges of water and may require evaluation of the ecological and biological impact of our operations and could require modifications to water intake structures or more stringent limitations on wastewater discharges. Depending upon the scope of modifications ultimately required by state regulators, these capital expenditures could be significant. The management and disposal of coal ash is regulated under the Resource Conservation and Recovery Act and the CCR Rule, which require the closure of our surface impoundments at Ameren Missouri’s coal-fired energy centers. The individual or combined effects of existing and new environmental regulations could result in significant capital expenditures, increased operating costs, or the closure or alteration of operations at some of Ameren Missouri’s energy centers. Ameren and Ameren Missouri expect that such compliance costs would be recoverable through rates, subject to MoPSC prudence review, but the timing of costs and their recovery could be subject to regulatory lag. Ameren and Ameren Missouri estimate that they will need to make capital expenditures of $125 million to $175 million from 2022 through 2026 in order to comply with existing environmental regulations. Additional environmental controls beyond 2026 could be required. This estimate of capital expenditures includes ash pond closure and corrective action measures required by the CCR Rule, and the effluent limitation guidelines applicable to steam electric generating units, and potential modifications to cooling water intake structures at existing power plants under Clean Water Act rules, all of which are discussed below. In addition to planned retirements of coal-fired energy centers as set forth in the 2020 IRP and as noted in the NSR and Clean Air Act litigation discussed below, Ameren Missouri’s current plan for compliance with existing air emission regulations includes natural gas-fired energy center retirements as discussed below in Illinois Emission Standards, burning low-sulfur coal and installing new or optimizing existing air pollution control equipment. The actual amount of capital expenditures required to comply with existing environmental regulations may vary substantially from the above estimates because of uncertainty as to future permitting requirements made by state regulators and the EPA, potential revisions to regulatory obligations, and the cost of potential compliance strategies, among other things. The following sections describe the more significant environmental laws and rules and environmental enforcement and remediation matters that affect or could affect our operations. The EPA has initiated an administrative review of several regulations and proposed amendments to regulations and guidelines, including to the effluent limitation guidelines and the CCR Rule, which could ultimately result in the revision of all or part of such rules. Additionally, Ameren Missouri’s wind generation facilities may be subject to operating restrictions to limit the impact on protected species. From April 2021 through October 2021, Ameren Missouri's High Prairie Renewable Energy Center curtailed nighttime operations to limit impacts on protected species. Ameren Missouri resumed nighttime operations in November 2021 as the critical biological season had ended. Seasonal nighttime curtailment will begin again in April 2022, but the extent and duration of the curtailment is unknown at this time as assessment of mitigation technologies is ongoing. Ameren Missouri does not anticipate these operating curtailments to result in significant impacts on its results of operations, financial position, or liquidity. Clean Air Act Federal and state laws, including CSAPR, regulate emissions of SO 2 and NO x through the reduction of emissions at their source and the use and retirement of emission allowances. CSAPR is implemented through a series of phases, and the second phase became effective in 2017. Additional emission reduction requirements may apply in subsequent years. Ameren Missouri complies with current CSAPR requirements by minimizing emissions through the use of low-sulfur coal, operation of two scrubbers at its Sioux Energy Center, and optimization of other existing air pollution control equipment. Ameren Missouri could incur additional costs to lower its emissions at one or more of its energy centers to comply with additional CSAPR requirements in future years. These additional costs for compliance are expected to be recovered from customers through the FAC or higher base rates. CO 2 Emissions Standards The EPA’s Affordable Clean Energy Rule repealed the Clean Power Plan and replaced it with a new rule that established emission guidelines for states to follow in developing plans to limit CO 2 emissions and identified certain efficiency measures as the best system of emission reduction for coal-fired electric generating units. In January 2021, the United States Court of Appeals for the District of Columbia Circuit vacated the Affordable Clean Energy Rule, and ruled that the EPA had the discretion to consider emission reduction measures that include efficiency measures and generation shifting to lower carbon emissions. The United States Supreme Court agreed to review the court of appeals’ ruling and oral arguments will occur in February 2022 with a decision expected by mid-2022. A decision by the United States Supreme Court could impact the EPA’s development of new regulations to address carbon emissions from coal- and natural gas-fired electric generating units. At this time, Ameren Missouri cannot predict the outcome of the legal challenge or future rulemakings. As such, any impact on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri is uncertain. NSR and Clean Air Act Litigation In January 2011, the United States Department of Justice, on behalf of the EPA, filed a complaint against Ameren Missouri in the United States District Court for the Eastern District of Missouri alleging that in performing projects at its coal-fired Rush Island Energy Center in 2007 and 2010, Ameren Missouri violated provisions of the Clean Air Act and Missouri law. In January 2017, the district court issued a liability ruling against Ameren Missouri and, in September 2019, entered a remedy order that required Ameren Missouri to install a flue gas desulfurization system at the Rush Island Energy Center and a dry sorbent injection system at the Labadie Energy Center. Ameren Missouri appealed both the liability and remedy orders and, in August 2021, the United States Court of Appeals for the Eighth Circuit issued a decision that affirmed the liability ruling and the district court’s remedy order as it related to the installation of a flue gas desulfurization system at the Rush Island Energy Center, but reversed the order as it related to the installation of a dry sorbent injection system at the Labadie Energy Center. In November 2021, the court of appeals issued an order denying requests for consideration previously sought by both Ameren Missouri and the United States Department of Justice. Based on its assessment of available legal, operational and regulatory alternatives, Ameren Missouri has determined not to further appeal the court rulings and, in December 2021, filed a motion with the district court to modify the remedy order to allow the retirement of the Rush Island Energy Center in advance of its previously expected useful life in lieu of installing a flue gas desulfurization system. The district court is under no deadline to issue a ruling revising the remedy order. In January 2022, the MISO completed a preliminary assessment regarding potential impacts of the retirement to the regional electric power system, which indicated transmission upgrades and voltage support would be needed in advance of the retirement to address reliability concerns. In February 2022, Ameren Missouri expects to formally notify the MISO of its intent to retire the Rush Island Energy Center. Upon receipt of the formal notification, the MISO will conduct a final reliability assessment. The MISO must also separately approve the specific upgrades and transmission support required to address reliability concerns noted in the assessment. Related to this matter, in February 2022, the MoPSC issued an order directing the MoPSC staff to review the planned accelerated retirement of the Rush Island Energy Center. See Note 2 – Rate and Regulatory Matters for additional information. In connection with the planned accelerated retirement of the Rush Island Energy Center, Ameren Missouri expects to seek approval from the MoPSC to finance the costs associated with the retirement, including the remaining unrecovered net plant balance associated with the facility, through the issuance of securitized utility tariff bonds pursuant to the Missouri securitization statute that became effective in August 2021. As of December 31, 2021, the Rush Island Energy Center had a net plant balance of approximately $0.6 billion included in plant to be abandoned, net, within “Property, Plant, and Equipment, Net” and a rate base of approximately $0.4 billion. See Note 1 – Summary of Significant Accounting Policies for additional information regarding plant to be abandoned, net. In addition, Ameren Missouri expects to file an update to the 2020 IRP with the MoPSC in the first half of 2022 to reflect the planned acceleration of the retirement of the Rush Island Energy Center from 2039, the retirement year for the facility as reflected in the 2020 IRP and reflected in depreciation rates approved by the December 2021 MoPSC electric rate order. Ameren Missouri is unable to predict the ultimate resolution of this matter; however, such resolution could have a material adverse effect on the results of operations, financial position, and liquidity of Ameren and Ameren Missouri. Clean Water Act The EPA’s regulations implementing Section 316(b) of the Clean Water Act require power plant operators to evaluate cooling water intake structures and identify measures for reducing the number of aquatic organisms impinged on a power plant’s cooling water intake screens or entrained through the plant’s cooling water system. All of Ameren Missouri’s coal-fired and nuclear energy centers are subject to the cooling water intake structures rule. Requirements of the rule are implemented by state regulators through the permit renewal process of each power plant’s water discharge permit, which is expected to be completed by 2023 for Ameren Missouri. In 2015, the EPA issued a rule to revise the effluent limitation guidelines applicable to steam electric generating units. These guidelines established national standards for water discharges, prohibit effluent discharges of certain waste streams, and impose more stringent limitations on certain water discharges from power plants. To meet the requirements of the guidelines, Ameren Missouri installed dry ash handling systems and in 2020 completed construction of wastewater treatment facilities at three of its four coal-fired energy centers. The Meramec Energy Center is scheduled to retire in 2022 and, as a result, does not require new wastewater and dry ash handling systems. CCR Management The EPA’s CCR Rule establishes requirements for the management and disposal of CCR from coal-fired power plants and will result in the closure of surface impoundments at Ameren Missouri’s energy centers. Ameren Missouri completed the closure of all surface impoundments at two of its facilities in 2021, and has made significant progress by closing several impoundments at its other two facilities. Ameren Missouri plans to complete the closures of the remaining surface impoundments in 2023. In January 2022, Ameren Missouri received notice of a proposed determination by the EPA that it has rejected Ameren Missouri’s requests to extend the timeline for operating certain impoundments located at the Sioux and Meramec energy centers. Compliance with the CCR Rule’s requirements for closure of the impoundments would be required 135 days after the EPA issues a final determination, which Ameren Missouri expects to be issued in the spring of 2022. If Ameren Missouri was no longer able to use the surface impoundments at the Sioux or Meramec energy centers, Ameren Missouri would not be able to operate the energy centers unless an alternative for handling the CCR material is in place. Ameren Missouri plans to retire the Meramec Energy Center in 2022, and is accelerating its construction plans to build a CCR Rule-compliant impoundment at the Sioux Energy Center to allow for continued operations. Additionally, Ameren Missouri is seeking a reliability determination from the MISO, which, if granted, would extend the deadline to comply with the requirement to close the impoundments and allow the energy centers to operate. Ameren Missouri does not expect that this matter will have a material adverse effect on its results of operations, financial position, or liquidity. Ameren and Ameren Missouri have AROs of $76 million recorded on their respective balance sheets as of December 31, 2021, associated with CCR storage facilities. Ameren Missouri estimates it will need to make capital expenditures of $60 million to $80 million from 2022 through 2026 to implement its CCR management compliance plan, which includes installation of groundwater monitoring equipment and groundwater treatment facilities. Remediation The Ameren Companies are involved in a number of remediation actions to clean up sites impacted by the use or disposal of materials containing hazardous substances. Federal and state laws can require responsible parties to fund remediation regardless of their degree of fault, the legality of original disposal, or the ownership of a disposal site. As of December 31, 2021, Ameren Illinois has remediated the majority of the 44 former MGP sites in Illinois and could substantially conclude remediation efforts at the remaining sites by 2023. The ICC allows Ameren Illinois to recover such remediation and related litigation costs from its electric and natural gas utility customers through environmental cost riders that are subject to annual prudence reviews by the ICC. As of December 31, 2021, Ameren Illinois estimated the remaining obligation related to these former MGP sites at $71 million to $125 million. Ameren and Ameren Illinois recorded a liability of $71 million to represent the estimated minimum obligation for these sites, as no other amount within the range was a better estimate. The scope of the remediation activities at these former MGP sites may increase as remediation efforts continue. Considerable uncertainty remains in these estimates because many site-specific factors can influence the actual costs, including unanticipated underground structures, the degree to which groundwater is encountered, regulatory changes, local ordinances, and site accessibility. The actual costs and timing of completion may vary substantially from these estimates. Our operations or those of our predecessor companies involve the use of, disposal of, and, in appropriate circumstances, the cleanup of substances regulated under environmental laws. We are unable to determine whether such historical practices will result in future environmental commitments or will affect our results of operations, financial position, or liquidity. Illinois Emission Standards The IETL established emission standards that became effective in September 2021. Ameren Missouri's natural gas-fired energy centers in Illinois will be subject to limits on emissions, including CO 2 and NOx, equal to their unit-specific average emissions from 2018 through 2020, for any rolling twelve-month period beginning October 1, 2021, through 2029. Further reductions to emissions limits will become effective between 2030 and 2040, which could limit the operations of Ameren Missouri's five natural gas-fired energy centers located in the state of Illinois, and will result in the closure of one or more energy centers earlier than anticipated. These energy centers are utilized to support peak loads. Subject to conditions in the IETL, these energy centers may be allowed to exceed the emissions limits in order to maintain reliability of electric utility service as necessary. Ameren Missouri is reviewing the emission standards and the effect they may have on its generation strategy, including any increases in capital expenditures or operating costs, and changes to the useful lives of the five natural gas-fired energy centers. Ameren Missouri expects to file an update to the 2020 IRP with the MoPSC in the first half of 2022 to reflect, among other things, the impact of these new emissions standards.

Supplemental Information

Supplemental Information	12 Months Ended
	Dec. 31, 2021
Supplemental Information [Abstract]
Supplemental Information	SUPPLEMENTAL INFORMATION Cash, Cash Equivalents, and Restricted Cash The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Cash and cash equivalents $ 8 $ — $ — $ 139 $ 136 $ — Restricted cash included in “Other current assets” 16 4 6 17 5 6 Restricted cash included in “Other assets” 127 — 127 141 — 141 Restricted cash included in “Nuclear decommissioning trust fund” 4 4 — 4 4 — Total cash, cash equivalents, and restricted cash $ 155 $ 8 $ 133 $ 301 $ 145 $ 147 Restricted cash included in “Other current assets” primarily represents funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees. Restricted cash included in “Other assets” on Ameren’s and Ameren Illinois’ balance sheets primarily represents amounts collected under a cost recovery rider restricted for use in the procurement of renewable energy credits and amounts in a trust fund restricted for the use of funding certain asbestos-related claims. Accounts Receivable “Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At December 31, 2021 and 2020, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $27 million and $28 million, respectively. The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the years ended December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Missouri Ameren Illinois (a) Ameren Ameren Missouri Ameren Illinois (a) Ameren Beginning of period $ 16 $ 34 $ 50 $ 7 $ 10 $ 17 Bad debt expense 5 4 (b) 9 15 33 48 Net write-offs (8) (22) (30) (6) (9) (15) End of period $ 13 $ 16 $ 29 $ 16 $ 34 $ 50 (a) Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. (b) In 2021, Ameren Illinois’ bad debt expense was reduced as a result of incremental state funding received for customer bill assistance. The incremental state funding granted relief to low-income customers at risk of service disconnection resulting from the impacts of the COVID-19 pandemic. Net write-offs increased for the year ended December 31, 2021 due to the resumption of disconnection activities for nonpayment. See Note 2 – Rate and Regulatory Matters for additional information. Inventories The following table presents the components of inventories for each of the Ameren Companies at December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Fuel (a) $ 118 $ — $ 118 $ 115 $ — $ 115 Natural gas stored underground 9 90 99 5 52 57 Materials, supplies, and other 292 83 375 266 83 349 Total inventories $ 419 $ 173 $ 592 $ 386 $ 135 $ 521 (a) Consists of coal, oil, and propane. Property, Plant, and Equipment In January 2021, Ameren Missouri acquired a 300-MW wind generation project located in northwestern Missouri. As of June 30, 2021, Ameren Missouri had placed the project in service as the Atchison Renewable Energy Center. The purchase price of the energy center was approximately $500 million, including an immaterial amount of transaction costs. In December 2020, Ameren Missouri acquired a 400-MW wind generation project located in northeastern Missouri for approximately $615 million, and placed the assets in service as the High Prairie Renewable Energy Center. The purchase price included $564 million of cash, a deferred purchase price obligation withheld as credit support in relation to certain potential claims, contingent consideration, and transaction costs. Both renewable energy centers support Ameren Missouri’s compliance with the Missouri renewable energy standard. Asset Retirement Obligations The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Beginning balance at January 1 $ 751 $ 5 (a) $ 756 (b) $ 687 $ 4 $ 691 Liabilities incurred 18 (c) — 18 (c) 36 (c) — 36 (c) Liabilities settled (36) (1) (37) (58) — (58) Accretion (d) 31 — 31 29 1 30 Change in estimates (4) (e) — (4) (e) 57 (f) — 57 (f) Ending balance at December 31 $ 760 (g) $ 4 (a) $ 764 (b)(g) $ 751 $ 5 (a) $ 756 (b) (a) Included in “Other deferred credits and liabilities” on the balance sheet. (b) Balance included $7 million and $60 million in “Other current liabilities” on the balance sheet as of December 31, 2021 and 2020, respectively. (c) Ameren Missouri recorded AROs related to the decommissioning of the Atchison Renewable and High Prairie Renewable energy centers in 2021 and 2020, respectively. (d) Accretion expense attributable to Ameren Missouri and Ameren Illinois was recorded as a decrease to regulatory liabilities and an increase to regulatory assets, respectively. (e) Ameren Missouri changed its fair value estimate primarily due to a decrease in the cost estimate for closure of certain CCR storage facilities, partially offset by an increase due to the planned accelerated retirement of the Rush Island Energy Center. (f) Ameren Missouri changed its fair value estimate primarily due to an update to the decommissioning of the Callaway Energy Center to reflect the cost study and funding analysis filed with the MoPSC in November 2020 and an increase in the cost estimate for closure of certain CCR storage facilities. (g) The balance as of December 31, 2021, included an ARO related to the decommissioning of the Callaway Enter Center of $574 million. Noncontrolling Interests As of December 31, 2021 and 2020, Ameren’s noncontrolling interests included the preferred stock of Ameren Missouri and Ameren Illinois. Deferred Compensation As of December 31, 2021, and 2020, the present value of benefits to be paid for deferred compensation obligations was $91 million and $90 million, respectively, which was primarily reflected in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. Excise Taxes Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes, that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri $ 150 $ 139 $ 147 Ameren Illinois 125 115 117 Ameren $ 275 $ 254 $ 264 Allowance for Funds Used During Construction The following table presents the average rate that was applied to eligible construction work in progress and the amounts of allowance for funds used during construction capitalized in 2021, 2020, and 2019: 2021 2020 2019 Average rate: Ameren Missouri 6 % 5 % 6 % Ameren Illinois 5 % 5 % 5 % Ameren: Allowance for equity funds used during construction $ 43 $ 32 $ 28 Allowance for borrowed funds used during construction 17 16 20 Total Ameren $ 60 $ 48 $ 48 Ameren Missouri: Allowance for equity funds used during construction $ 26 $ 19 $ 19 Allowance for borrowed funds used during construction 10 10 12 Total Ameren Missouri $ 36 $ 29 $ 31 Ameren Illinois: Allowance for equity funds used during construction $ 17 $ 13 $ 9 Allowance for borrowed funds used during construction 7 6 8 Total Ameren Illinois $ 24 $ 19 $ 17 Earnings per Share Earnings per basic and diluted share are computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of basic and diluted common shares outstanding, respectively, during the applicable period. The weighted-average shares outstanding for earnings per diluted share includes the incremental effects resulting from performance share units, restricted stock units, and forward sale agreements relating to common stock when the impact would be dilutive, as calculated using the treasury stock method. For information regarding performance share units and restricted stock units, see Note 11 – Stock-based Compensation. For information regarding forward sale agreements, see Note 5 – Long-term Debt and Equity Financings. The following table reconciles the weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Weighted-average Common Shares Outstanding – Basic 256.3 247.0 245.6 Assumed settlement of performance share units and restricted stock units 1.3 1.2 1.4 Dilutive effect of forward sale agreements — 0.5 0.1 Weighted-average Common Shares Outstanding – Diluted (a) 257.6 248.7 247.1 (a) There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations for the year ended December 31, 2021. There were no potentially dilutive securities excluded from the earnings per diluted share calculations for the years ended December 31, 2020 and 2019. Supplemental Cash Flow Information The following table provides noncash financing and investing activity excluded from the statements of cash flows for the years ended December 31, 2021, 2020, and 2019: December 31, 2021 December 31, 2020 December 31, 2019 Ameren Ameren Ameren Ameren Ameren Ameren Ameren Ameren Ameren Investing Accrued capital expenditures, including wind generation expenditures $ 508 $ 285 $ 215 $ 446 $ 229 $ 218 $ 333 $ 140 $ 163 Accrued nuclear fuel expenditures 16 16 — — — — 19 19 — Net realized and unrealized gain – nuclear decommissioning trust fund 163 163 — 116 116 — 143 143 — Exchange of bond investments for the extinguishment of senior unsecured notes (a) — — — — — — 17 — 17 Financing Issuance of common stock for stock-based compensation $ 33 $ — $ — $ 38 $ — $ — $ 54 $ — $ — Exchange of bond investments for the extinguishment of senior unsecured notes (a) — — — — — — (17) — (17) (a) In 2006, Ameren Illinois purchased all $17 million of the 1993 Series B-1 bonds due 2028 issued by the Illinois Finance Authority on behalf of Ameren Illinois pursuant to a mandatory tender. Ameren Illinois’ 1993 Series B-1 senior unsecured notes due 2028 were not extinguished and remained as “Long-term debt, net” on Ameren’s and Ameren Illinois’ balance sheets. In September 2019, Ameren Illinois exchanged its bond investments for the extinguishment of its senior unsecured notes.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION Ameren has four segments: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. The Ameren Missouri segment includes all of the operations of Ameren Missouri. Ameren Illinois Electric Distribution consists of the electric distribution business of Ameren Illinois. Ameren Illinois Natural Gas consists of the natural gas business of Ameren Illinois. Ameren Transmission primarily consists of the aggregated electric transmission businesses of Ameren Illinois and ATXI. The category called Other primarily includes Ameren (parent) activities and Ameren Services. Ameren Missouri has one segment. Ameren Illinois has three segments: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. See Note 1 – Summary of Significant Accounting Policies for additional information regarding the operations of Ameren Missouri, Ameren Illinois, and ATXI. Segment operating revenues and a majority of operating expenses are directly recognized and incurred by Ameren Illinois to each Ameren Illinois segment. Common operating expenses, miscellaneous income and expenses, interest charges, and income tax expense are allocated by Ameren Illinois to each Ameren Illinois segment based on certain factors, which primarily relate to the nature of the cost. Additionally, Ameren Illinois Transmission earns revenue from transmission service provided to Ameren Illinois Electric Distribution, other retail electric suppliers, and wholesale customers. The transmission expense for Illinois customers who have elected to purchase their power from Ameren Illinois is recovered through a cost recovery mechanism with no net effect on Ameren Illinois Electric Distribution earnings, as costs are offset by corresponding revenues. Transmission revenues from these transactions are reflected in Ameren Transmission’s and Ameren Illinois Transmission’s operating revenues. An intersegment elimination at Ameren and Ameren Illinois occurs to eliminate these transmission revenues and expenses. The following tables present information about the reported revenue and specified items reflected in net income attributable to common shareholders and capital expenditures by segment at Ameren and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Other Intersegment Eliminations Ameren 2021 External revenues $ 3,311 $ 1,635 $ 957 $ 491 $ — $ — $ 6,394 Intersegment revenues 42 4 — 71 — (117) — Depreciation and amortization 632 309 90 111 4 — 1,146 Interest income 26 1 — — 3 (3) 27 Interest charges 137 74 42 83 (a) 50 (3) 383 Income taxes (benefit) 3 53 39 82 (20) — 157 Net income (loss) attributable to Ameren common shareholders 518 165 108 230 (31) — 990 Capital expenditures 2,015 (b) 579 278 616 4 (13) 3,479 (b) 2020 External revenues $ 3,069 $ 1,496 $ 760 $ 469 $ — $ — $ 5,794 Intersegment revenues 40 2 — 54 — (96) — Depreciation and amortization 604 288 81 98 4 — 1,075 Interest income 26 2 — 1 4 (4) 29 Interest charges 190 72 41 78 (a) 42 (4) 419 Income taxes (benefit) 34 42 36 78 (35) — 155 Net income (loss) attributable to Ameren common shareholders 436 143 99 216 (23) — 871 Capital expenditures 1,666 (b) 543 301 716 5 2 3,233 (b) 2019 External revenues $ 3,212 $ 1,487 $ 791 $ 401 $ — $ — $ 5,891 Intersegment revenues 31 17 6 63 — (98) 19 (c) Depreciation and amortization 556 273 78 84 4 — 995 Interest income 26 6 — 1 5 (5) 33 Interest charges 178 71 38 74 (a) 25 (5) 381 Income taxes (benefit) 68 45 30 64 (25) — 182 Net income (loss) attributable to Ameren common shareholders 426 146 84 185 (13) — 828 Capital expenditures 1,076 518 318 528 3 (32) (d) 2,411 (a) Ameren Transmission interest charges include an allocation of financing costs from Ameren (parent). (b) Includes $525 million and $564 million at Ameren and Ameren Missouri for wind generation expenditures for the year ended December 31, 2021 and 2020, respectively. (c) Intersegment revenues at Ameren include $14 million and $5 million of revenue from Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively, for the year ended December 31, 2019, for a software licensing agreement with Ameren Missouri. Under authoritative accounting guidance for rate-regulated entities, the revenue recognized by Ameren Illinois was not eliminated upon consolidation. See Note 13 – Related-party Transactions for additional information. (d) Intersegment capital expenditure eliminations include $24 million of eliminations for the year ended December 31, 2019, for a software licensing agreement between Ameren Illinois and Ameren Missouri. See Note 13 – Related-party Transactions for additional information. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois 2021 External revenues $ 1,639 $ 957 $ 299 $ — $ 2,895 Intersegment revenues — — 66 (66) — Depreciation and amortization 309 90 73 — 472 Interest income 1 — — — 1 Interest charges 74 42 48 — 164 Income taxes 53 39 51 — 143 Net income available to common shareholder 165 108 152 — 425 Capital expenditures 579 278 575 — 1,432 2020 External revenues $ 1,498 $ 760 $ 277 $ — $ 2,535 Intersegment revenues — — 52 (52) — Depreciation and amortization 288 81 65 — 434 Interest income 2 — 1 — 3 Interest charges 72 41 42 — 155 Income taxes 42 36 46 — 124 Net income available to common shareholder 143 99 137 — 379 Capital expenditures 543 301 603 — 1,447 2019 External revenues $ 1,504 $ 797 $ 226 $ — $ 2,527 Intersegment revenues — — 62 (62) — Depreciation and amortization 273 78 55 — 406 Interest income 6 — — — 6 Interest charges 71 38 38 — 147 Income taxes 45 30 35 — 110 Net income available to common shareholder 146 84 113 — 343 Capital expenditures 518 318 372 — 1,208 The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Intersegment Eliminations Ameren 2021 Residential $ 1,445 $ 933 $ — $ — $ — $ 2,378 Commercial 1,126 545 — — — 1,671 Industrial 280 135 — — — 415 Other 361 26 — 562 (116) 833 Total electric revenues $ 3,212 $ 1,639 $ — $ 562 $ (116) $ 5,297 Residential $ 79 $ — $ 657 $ — $ — $ 736 Commercial 34 — 172 — — 206 Industrial 4 — 35 — — 39 Other 24 — 93 — (1) 116 Total gas revenues $ 141 $ — $ 957 $ — $ (1) $ 1,097 Total revenues (a) $ 3,353 $ 1,639 $ 957 $ 562 $ (117) $ 6,394 2020 Residential $ 1,373 $ 867 $ — $ — $ — $ 2,240 Commercial 1,025 486 — — — 1,511 Industrial 261 124 — — — 385 Other 325 21 — 523 (94) 775 Total electric revenues $ 2,984 $ 1,498 $ — $ 523 $ (94) $ 4,911 Residential $ 76 $ — $ 541 $ — $ — $ 617 Commercial 29 — 136 — — 165 Industrial 4 — 14 — — 18 Other 16 — 69 — (2) 83 Total gas revenues $ 125 $ — $ 760 $ — $ (2) $ 883 Total revenues (a) $ 3,109 $ 1,498 $ 760 $ 523 $ (96) $ 5,794 2019 Residential $ 1,403 $ 848 $ — $ — $ — $ 2,251 Commercial 1,157 497 — — — 1,654 Industrial 278 127 — — — 405 Other 271 32 (b) — 464 (96) 671 Total electric revenues $ 3,109 $ 1,504 $ — $ 464 $ (96) $ 4,981 Residential $ 81 $ — $ 570 $ — $ — $ 651 Commercial 34 — 154 — — 188 Industrial 4 — 13 — — 17 Other 15 — 60 (b) — (2) 73 Total gas revenues $ 134 $ — $ 797 $ — $ (2) $ 929 Total revenues (a) $ 3,243 $ 1,504 $ 797 $ 464 $ (98) $ 5,910 (a) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the years ended December 31, 2021, 2020, and 2019: Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Ameren 2021 Revenues from alternative revenue programs $ (16) $ 77 $ 5 $ 11 $ 77 Other revenues not from contracts with customers 56 (a) 10 2 — 68 (a) 2020 Revenues from alternative revenue programs $ (14) $ (20) $ 20 $ 50 $ 36 Other revenues not from contracts with customers 25 8 2 1 36 2019 Revenues from alternative revenue programs $ 35 $ (74) $ — $ (31) $ (70) Other revenues not from contracts with customers 19 7 2 — 28 (a) Includes insurance recoveries related to lost sales associated with the Callaway Energy Center maintenance outage. See Note 9 – Callaway Energy Center for additional information. (b) Includes $14 million and $5 million for Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively, for the year ended December 31, 2019, for a software licensing agreement with Ameren Missouri. See Note 13 – Related-party Transactions for additional information. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois 2021 Residential $ 933 $ 657 $ — $ — $ 1,590 Commercial 545 172 — — 717 Industrial 135 35 — — 170 Other 26 93 365 (66) 418 Total revenues (a) $ 1,639 $ 957 $ 365 $ (66) $ 2,895 2020 Residential $ 867 $ 541 $ — $ — $ 1,408 Commercial 486 136 — — 622 Industrial 124 14 — — 138 Other 21 69 329 (52) 367 Total revenues (a) $ 1,498 $ 760 $ 329 $ (52) $ 2,535 2019 Residential $ 848 $ 570 $ — $ — $ 1,418 Commercial 497 154 — — 651 Industrial 127 13 — — 140 Other 32 (b) 60 (b) 288 (62) 318 Total revenues (a) $ 1,504 $ 797 $ 288 $ (62) $ 2,527 (a) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the years ended December 31, 2021, 2020, and 2019: Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Ameren Illinois 2021 Revenues from alternative revenue programs $ 77 $ 5 $ 9 $ 91 Other revenues not from contracts with customers 10 2 — 12 2020 Revenues from alternative revenue programs $ (20) $ 20 $ 42 $ 42 Other revenues not from contracts with customers 8 2 — 10 2019 Revenues from alternative revenue programs $ (74) $ — $ (33) $ (107) Other revenues not from contracts with customers 7 2 — 9 (b) Includes $14 million and $5 million for Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively, for the year ended December 31, 2019, for a software licensing agreement with Ameren Missouri. See Note 13 – Related-party Transactions for additional information.

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information Of Parent	12 Months Ended
	Dec. 31, 2021
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information Of Parent	SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT AMEREN CORPORATION CONDENSED STATEMENT OF INCOME AND COMPREHENSIVE INCOME For the Years Ended December 31, 2021, 2020, and 2019 (In millions) 2021 2020 2019 Operating revenues $ — $ — $ — Operating expenses 13 12 15 Operating loss (13) (12) (15) Equity in earnings of subsidiaries 1,039 908 850 Interest income from affiliates 3 4 5 Total other expense, net — (8) (2) Interest charges (64) (57) (39) Income tax benefit 25 36 29 Net Income Attributable to Ameren Common Shareholders $ 990 $ 871 $ 828 Net Income Attributable to Ameren Common Shareholders $ 990 $ 871 $ 828 Other Comprehensive Income, Net of Taxes: Pension and other postretirement benefit plan activity, net of income taxes of $4, $5, and $1, respectively 14 16 5 Comprehensive Income Attributable to Ameren Common Shareholders $ 1,004 $ 887 $ 833 SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT (In millions, except per share amounts) December 31, 2021 December 31, 2020 Assets: Cash and cash equivalents $ — $ — Advances to money pool 108 16 Accounts receivable – affiliates 30 12 Miscellaneous accounts and notes receivable 11 15 Other current assets 4 4 Total current assets 153 47 Investments in subsidiaries 12,281 10,872 Note receivable – ATXI 35 75 Accumulated deferred income taxes, net 65 42 Other assets 184 167 Total assets $ 12,718 $ 11,203 Liabilities and Shareholders’ Equity: Short-term debt $ 277 $ 490 Taxes accrued 7 — Accounts payable – affiliates 53 41 Other current liabilities 38 34 Total current liabilities 375 565 Long-term debt 2,533 1,588 Pension and other postretirement benefits 24 27 Other deferred credits and liabilities 86 85 Total liabilities 3,018 2,265 Commitments and Contingencies (Note 5) Shareholders’ Equity: Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 257.7 and 253.3, respectively 3 3 Other paid-in capital, principally premium on common stock 6,502 6,179 Retained earnings 3,182 2,757 Accumulated other comprehensive income (loss) 13 (1) Total shareholders’ equity 9,700 8,938 Total liabilities and shareholders’ equity $ 12,718 $ 11,203 SCHEDULE I – CONDENSED FINANCIAL INFORMATION OF PARENT AMEREN CORPORATION CONDENSED STATEMENT OF CASH FLOWS For the Years Ended December 31, 2021, 2020, and 2019 (In millions) 2021 2020 2019 Net cash flows provided by operating activities $ 79 $ 147 $ 491 Cash flows from investing activities: Money pool advances, net (92) 86 (26) Notes receivable – ATXI 40 — — Investments in subsidiaries (489) (956) (142) Other 7 8 5 Net cash flows used in investing activities (534) (862) (163) Cash flows from financing activities: Dividends on common stock (565) (494) (472) Short-term debt, net (213) 337 (317) Money pool borrowings, net — (24) (22) Maturities of long-term debt — (350) — Issuances of long-term debt 949 798 450 Issuances of common stock 308 476 68 Employee payroll taxes related to stock-based compensation (17) (20) (29) Debt issuance costs (7) (7) (4) Net cash flows provided by (used in) financing activities 455 716 (326) Net change in cash, cash equivalents, and restricted cash $ — $ 1 $ 2 Cash, cash equivalents, and restricted cash at beginning of year 4 3 1 Cash, cash equivalents, and restricted cash at end of year $ 4 $ 4 $ 3 Supplemental information: Cash dividends received from consolidated subsidiaries $ 123 $ 105 $ 445 Noncash financing activity – Issuance of common stock for stock-based compensation 33 38 54 AMEREN CORPORATION (parent company only) NOTES TO CONDENSED FINANCIAL STATEMENTS December 31, 2021 NOTE 1 – BASIS OF PRESENTATION Ameren Corporation (parent company only) is a public utility holding company that conducts substantially all of its business operations through its subsidiaries. Ameren Corporation (parent company only) has accounted for its subsidiaries using the equity method. These financial statements are presented on a condensed basis. See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of this report for additional information. NOTE 2 – CASH AND CASH EQUIVALENTS The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheet and the statement of cash flows as of December 31, 2021 and 2020: (In millions) 2021 2020 Cash and cash equivalents $ — $ — Restricted cash included in “Other current assets” 4 4 Total cash, cash equivalents, and restricted cash $ 4 $ 4 See Note 1 – Summary of Significant Accounting Policies under Part II, Item 8, of this report for additional information. NOTE 3 – SHORT-TERM DEBT AND LIQUIDITY Ameren, Ameren Services, and other non-state-regulated Ameren subsidiaries have the ability, subject to Ameren parent company and applicable regulatory short-term borrowing authorizations, to access funding from the Credit Agreements and the commercial paper programs through a non-state-regulated subsidiary money pool agreement. All participants may borrow from or lend to the non-state-regulated money pool. The total amount available to pool participants from the non-state-regulated subsidiary money pool at any given time is reduced by the amount of borrowings made by participants, but is increased to the extent that the pool participants advance surplus funds to the non-state-regulated subsidiary money pool or remit funds from other external sources. The non-state-regulated subsidiary money pool was established to coordinate and to provide short-term cash and working capital for the participants. Participants receiving a loan under the non-state-regulated subsidiary money pool agreement must repay the principal amount of such loan, together with accrued interest. The rate of interest depends on the composition of internal and external funds in the non-state-regulated subsidiary money pool. Interest revenues and interest charges related to non-state-regulated money pool advances and borrowings were immaterial in 2019, 2020, and 2021. See Note 4 – Short-term Debt and Liquidity under Part II, Item 8, of this report for a description and details of short-term debt and liquidity needs of Ameren Corporation (parent company only). NOTE 4 – LONG-TERM OBLIGATIONS See Note 5 – Long-term Debt and Equity Financings under Part II, Item 8, of this report for additional information on Ameren Corporation’s (parent company only) long-term debt, indenture provisions, forward sale agreements related to common stock, and ATM program. NOTE 5 – COMMITMENTS AND CONTINGENCIES See Note 14 – Commitments and Contingencies under Part II, Item 8, of this report for a description of all material contingencies of Ameren Corporation (parent company only). NOTE 6 – TOTAL OTHER EXPENSE, NET The following table presents the components of “Total Other Expense, Net” in the Condensed Statement of Income and Comprehensive Income for the years ended December 31, 2021, 2020, and 2019: (In millions) 2021 2020 2019 Total Other Expense, Net Non-service cost components of net periodic benefit income $ 1 $ 1 $ 2 Donations — (8) (3) Other expense, net (1) (1) (1) Total Other Expense, Net $ — $ (8) $ (2)
Schedule of Cash and Cash Equivalents Including Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Cash and cash equivalents $ 8 $ — $ — $ 139 $ 136 $ — Restricted cash included in “Other current assets” 16 4 6 17 5 6 Restricted cash included in “Other assets” 127 — 127 141 — 141 Restricted cash included in “Nuclear decommissioning trust fund” 4 4 — 4 4 — Total cash, cash equivalents, and restricted cash $ 155 $ 8 $ 133 $ 301 $ 145 $ 147 The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheet and the statement of cash flows as of December 31, 2021 and 2020: (In millions) 2021 2020 Cash and cash equivalents $ — $ — Restricted cash included in “Other current assets” 4 4 Total cash, cash equivalents, and restricted cash $ 4 $ 4
Other Income And Expenses	The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren: Other Income, Net Allowance for equity funds used during construction $ 43 $ 32 $ 28 Interest income on industrial development revenue bonds 25 25 25 Other interest income 2 4 8 Non-service cost components of net periodic benefit income (a) 136 116 90 Miscellaneous income 22 13 6 Donations (9) (25) (b) (12) Miscellaneous expense (17) (14) (15) Total Other Income, Net $ 202 $ 151 $ 130 Ameren Missouri: Other Income, Net Allowance for equity funds used during construction $ 26 $ 19 $ 19 Interest income on industrial development revenue bonds 25 25 25 Other interest income 1 1 1 Non-service cost components of net periodic benefit income (a) 55 46 18 Miscellaneous income 3 4 5 Donations (4) (12) (b) (3) Miscellaneous expense (7) (7) (7) Total Other Income, Net $ 99 $ 76 $ 58 2021 2020 2019 Ameren Illinois: Other Income, Net Allowance for equity funds used during construction $ 17 $ 13 $ 9 Interest income 1 3 6 Non-service cost components of net periodic benefit income (a) 55 48 47 Miscellaneous income 6 6 3 Donations (5) (5) (5) Miscellaneous expense (8) (6) (7) Total Other Income, Net $ 66 $ 59 $ 53 (a) For the years ended December 31, 2021, 2020, and 2019, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(7) million, $(4) million, and $29 million, respectively, due to a tracker for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. (b) Includes $8 million pursuant to Ameren Missouri’s March 2020 electric rate order. The following table presents the components of “Total Other Expense, Net” in the Condensed Statement of Income and Comprehensive Income for the years ended December 31, 2021, 2020, and 2019: (In millions) 2021 2020 2019 Total Other Expense, Net Non-service cost components of net periodic benefit income $ 1 $ 1 $ 2 Donations — (8) (3) Other expense, net (1) (1) (1) Total Other Expense, Net $ — $ (8) $ (2)

Schedule II - Valuation And Qua

Schedule II - Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Valuation And Qualifying Accounts	SCHEDULE II – VALUATION AND QUALIFYING ACCOUNTS FOR THE YEARS ENDED DECEMBER 31, 2021, 2020, AND 2019 (In millions) Column A Column B Column C Column D Column E Description Balance at (1) (2) Charged to Other Accounts (a) Deductions (b) Balance at End Ameren: Deducted from assets – allowance for doubtful accounts: 2021 $ 50 $ 9 $ — $ 30 $ 29 2020 17 42 6 15 50 2019 18 26 4 31 17 Ameren Missouri: Deducted from assets – allowance for doubtful accounts: 2021 $ 16 $ 5 $ — $ 8 $ 13 2020 7 15 — 6 16 2019 7 9 — 9 7 Ameren Illinois: Deducted from assets – allowance for doubtful accounts: 2021 $ 34 $ 4 $ — $ 22 $ 16 2020 10 27 6 9 34 2019 11 17 4 22 10 (a) Amounts associated with the allowance for doubtful accounts relate to the uncollectible account reserve associated with receivables purchased by Ameren Illinois from alternative retail electric suppliers, as required by the Illinois Public Utilities Act. (b) Uncollectible accounts charged off, less recoveries.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Nature of Operations	General Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has other subsidiaries that conduct other activities, such as providing shared services. • Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri, which includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers. • Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to a 43,700 square mile area in central and southern Illinois. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers. • Ameren Transmission Company of Illinois, doing business as ATXI, operates a FERC rate-regulated electric transmission business in the MISO. ATXI was incorporated in Illinois in 2006. In December 2020, ATXI completed construction of the ninth and final line segment of the Illinois Rivers transmission line, a MISO-approved electric transmission line. ATXI also operates the Spoon River and Mark Twain transmission lines, which were placed in service in February 2018 and December 2019, respectively.
Consolidation	Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated, except as disclosed in Note 13 – Related-party Transactions. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated. Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and
Public Utilities	Regulation Our customer rates are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be refunded to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. See Note 2 – Rate and Regulatory Matters for additional information on our regulatory frameworks, regulatory recovery mechanisms, and regulatory assets and liabilities recorded at December 31, 2021 and 2020. We continually assess the recoverability of our respective regulatory assets. Regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that reductions in customers’ rates or refunds to customers related to regulatory liabilities are no longer probable, the amounts are credited to earnings. Environmental Costs Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates. See Note 14 – Commitments and Contingencies for additional information on liabilities for environmental costs.
Cash and Cash Equivalents	Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents include short-term, highly liquid investments purchased with an original maturity of three months or less. Cash and cash equivalents subject to legal or contractual restrictions and not readily available for use for general corporate purposes are classified as restricted cash. See Note 15 – Supplemental Information for a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows.
Allowance for Doubtful Accounts Receivable	Allowance for Doubtful Accounts Receivable The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has bad debt riders that adjust rates for net write-offs of customer accounts receivable above or below those being collected in rates. In 2020, the rider for electric distribution allowed for recovery of bad debt expense recognized under GAAP.
Inventories	Inventories Inventories are recorded at the lower of weighted-average cost or net realizable value. Inventories are capitalized when purchased and then expensed as consumed or capitalized as property, plant, and equipment when installed, as appropriate. See Note 15 – Supplemental Information for the components of inventories.
Property and Plant	Property, Plant, and Equipment, Net We capitalize the cost of additions to, and betterments of, units of property, plant, and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures are expensed as incurred. Beginning in 2020, maintenance expenses related to scheduled Callaway nuclear refueling and maintenance outages, which were previously expensed as incurred, are deferred and amortized over the number of expected months until the completion of the next refueling outage, which historically has been approximately 18 months . When units of depreciable property are retired, the original costs, and the associated removal cost, net of salvage, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations section below and Note 3 – Property, Plant, and Equipment, Net for additional information. Ameren Missouri’s cost of nuclear fuel is capitalized as a part of “Property, Plant, and Equipment, Net” on the balance sheet and then amortized to “Operating Expenses – Fuel” in the statement of income on a unit-of-production basis. Plant to be Abandoned, Net When it becomes probable an asset will be retired significantly in advance of its previously expected useful life and in the near term, the Ameren Companies must assess the probability of full recovery of the remaining net book value of the asset to be abandoned. We recognize a loss on abandonment when it becomes probable that all or part of the cost of an asset, including a return at the applicable WACC, will be disallowed from recovery either through customer rates or through the issuance of securitized utility tariff bonds and such amount is reasonably estimable. An abandonment loss, if any, would equal the difference between the remaining net book value of the asset and the present value of the expected future cash flows. If the asset is still in service, the net book value is classified as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on the balance sheet. The net book value will be classified as a regulatory asset on the balance sheet when the asset is no longer in service or as required by a rate order. In relation to the NSR and Clean Air Act litigation discussed in Note 14 – Commitments and Contingencies, in December 2021, Ameren Missouri filed a motion with the United States District Court for the Eastern District of Missouri to modify a previously issued remedy order to allow the retirement of the Rush Island Energy Center in lieu of installing a flue gas desulfurization system. As of December 31, 2021, Ameren and Ameren Missouri determined that the Rush Island Energy Center met the criteria to be considered probable of abandonment and have classified its remaining net book value as plant to be abandoned, net, within “Property, Plant, and Equipment, Net” on Ameren’s and Ameren Missouri’s balance sheets. See Note 3 – Property, Plant, and Equipment, Net for our plant to be abandoned balance as of December 31, 2021. Ameren Missouri is currently allowed a full recovery of and a full return on its investment in Rush Island Energy Center and has concluded that no abandonment loss was required as of December 31, 2021. As part of the assessment of any potential future abandonment loss, consideration will be given to rate and securitization orders issued by the MoPSC to Ameren Missouri and to orders issued to other Missouri utilities with similar facts. Depreciation Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The composite rates include a provision for the estimated removal cost of property, plant, and equipment retired from service, net of salvage. The provision for depreciation for the Ameren Companies in 2021, 2020, and 2019 ranged from 3% to 4% of the average depreciable cost. See Note 3 – Property, Plant, and Equipment, Net for additional information on estimated depreciable lives.
Allowance for Funds Used During Construction	Allowance for Funds Used During Construction As a part of “Property, Plant, and Equipment, Net” on the balance sheet, we capitalize allowance for funds used during construction, which is the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to eligible rate-regulated construction work in progress, in accordance with the utility industry’s accounting practice and GAAP. The amount of allowance for funds used during construction is calculated using a FERC-prescribed formula based on a rate, which incorporates the average cost of short-term debt, the average cost of long-term debt, and the cost of equity funds. The portion attributable to borrowed funds is recorded as a reduction of “Interest Charges” on the statements of income. The portion attributable to equity funds is recorded within “Other Income, Net” on the statements of income. This accounting practice offsets the effect on earnings of the cost of financing during construction. See Note 15 – Supplemental Information for the amount of allowance for funds used during construction capitalized and the average rate applied to eligible construction work in progress. Allowance for funds used during construction does not represent a current source of cash funds. Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates.
Goodwill	Goodwill Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had goodwill of $411 million at December 31, 2021 and 2020. Ameren has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2021 and 2020. The Ameren Transmission reporting unit had the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit at December 31, 2021 and 2020. Ameren and Ameren Illinois evaluate goodwill for impairment in each of their reporting units as of October 31 each year, or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of their reporting units below their carrying amounts. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a quantitative test. Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2021. As part of this qualitative assessment, Ameren and Ameren Illinois evaluated, among other things, macroeconomic conditions, industry and market considerations such as observable industry market multiples, regulatory frameworks, cost factors, overall financial performance, and entity-specific events. The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was
Impairment of Long-lived Assets	Impairment of Long-lived Assets We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine that an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of long-lived assets may not be recoverable in 2021, 2020 or 2019.
Variable Interest Entities	Variable Interest Entities As of December 31, 2021 and 2020, Ameren had unconsolidated variable interests as a limited partner in various equity method investments, primarily to advance clean and resilient energy technologies, totaling $56 million and $37 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. Any earnings or losses related to these investments are included in “Other Income, Net” on Ameren’s consolidated statement of income and comprehensive income. Ameren is not the primary beneficiary of these investments because it does not have the power to direct matters that most significantly affect the activities of these variable interest entities. As of December 31, 2021, the maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $56 million plus associated outstanding funding commitments of $28 million .
Asset Retirement Obligations	Asset Retirement Obligations and Removal Costs We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs for accretion and changes in the estimated fair values of the obligations, with a corresponding increase or decrease in the asset book value for the fair value changes. Asset book values, reflected within “Property, Plant, and Equipment, Net” on the balance sheet, are depreciated over the remaining useful life of the related asset. Due to regulatory recovery, that depreciation is deferred as a regulatory balance. The depreciation of the asset book values at Ameren Missouri was $14 million , $28 million, and $18 million for the years ended December 31, 2021, 2020, and 2019, respectively, which was deferred as a reduction to the net regulatory liability. The net regulatory liability also reflects a deferral for the nuclear decommissioning trust fund balance for the Callaway Energy Center. The depreciation deferred to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with decommissioning of Ameren Missouri’s Callaway and wind renewable energy centers, certain Ameren Missouri solar energy centers, CCR facilities, and river structures at certain energy centers used for unloading coal and circulating water systems. Additionally, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. See Note 15 – Supplemental Information for a reconciliation of the beginning and ending carrying amounts of AROs. Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment retired from service, net of salvage, represent a cost of removal regulatory liability. See the cost of removal regulatory liability balance in Note 2 – Rate and Regulatory Matters.
Company-owned Life Insurance	Company-owned Life Insurance Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of December 31, 2021, the cash surrender value of company-owned life insurance at Ameren and Ameren Illinois was $278 million (December 31, 2020 – $272 million) and $117 million (December 31, 2020 – $115 million), respectively, while total borrowings against the policies were $109 million (December 31, 2020 – $107 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance
Operating Revenues	Operating Revenues We record revenues from contracts with customers for various electric and natural gas services, which primarily consist of retail distribution, electric transmission, and off-system arrangements. When more than one performance obligation exists in a contract, the consideration under the contract is allocated to the performance obligations based on the relative standalone selling price. Electric and natural gas retail distribution revenues are earned when the commodity is delivered to our customers. We accrue an estimate of electric and natural gas retail distribution revenues for service provided but unbilled at the end of each accounting period. Electric transmission revenues are earned as electric transmission services are provided. Off-system revenues are primarily comprised of MISO revenues and wholesale bilateral revenues. MISO revenues include the sale of electricity, capacity, and ancillary services. Wholesale bilateral revenues include the sale of electricity and capacity. MISO-related electricity and wholesale bilateral electricity revenues are earned as electricity is delivered. Capacity and ancillary service revenues are earned as services are provided. Retail distribution, electric transmission, and off-system revenues, including the underlying components described above, represent a series of goods or services that are substantially the same and have the same pattern of transfer over time to our customers. Revenues from contracts with customers are equal to the amounts billed and our estimate of electric and natural gas retail distribution services provided but unbilled at the end of each accounting period. Customers are billed at least monthly, and payments are due less than one month after goods and/or services are provided. See Note 16 – Segment Information for disaggregated revenue information. For certain regulatory recovery mechanisms that are alternative revenue programs rather than revenues from contracts with customers, we recognize revenues that have been authorized for rate recovery, are objectively determinable and probable of recovery, and are expected to be collected from customers within two years from the end of the year. Our alternative revenue programs include revenue requirement reconciliations, the MEEIA, the VBA, and the WNAR. These revenues are subsequently recognized as revenues from contracts with customers when billed, with an offset to alternative revenue program revenues. As of December 31, 2021 and 2020, our remaining performance obligations were immaterial. The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less.
Cost Of Sales	Accounting for MISO Transactions MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by the MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri’s and Ameren Illinois’ prior-period transactions will be resettled outside the routine settlement process because of a change in the MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize revenues and expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. There were no material MISO resettlements in 2021, 2020, or 2019.
Stock-Based Compensation	Stock-based Compensation Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite vesting period. To the extent that actual forfeitures differ from estimated forfeitures, such differences are accounted for as a cumulative adjustment to compensation expense and recorded in the period that estimates are revised. Compensation cost is ultimately recognized only for awards for which the requisite service was provided. See Note 11 – Stock-based Compensation for additional information.
Unamortized Debt Discount, Premium, And Expense	Unamortized Debt Discounts, Premiums, and Issuance Costs Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of the agreement.
Income Taxes	Income Taxes Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates. We expect that regulators will reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in certain deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases. To the extent deferred tax balances are included in rate base, the revaluation of deferred taxes is recorded as a regulatory asset or liability on the balance sheet and will be collected from, or refunded to, customers. For deferred tax balances not included in rate base, the revaluation of deferred taxes is recorded as an adjustment to income tax expense on the income statement. See Note 12 – Income Taxes for further information regarding the revaluation of deferred taxes related to Missouri state corporate income tax rate changes. Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax using a stand-alone calculation, which is similar to what would be owed or refunded had the party been separately subject to tax without considering the impact of consolidation. Any net benefit attributable to Ameren (parent) is reallocated to the other parties. This reallocation is treated as a capital contribution to the party receiving the benefit. See Note 13 – Related-party Transactions for information regarding capital contributions under the tax allocation agreement.
Derivatives, Policy	We use derivatives to manage the risk of changes in market prices for natural gas, power, and uranium, as well as the risk of changes in rail transportation surcharges through fuel oil hedges. Such price fluctuations may cause the following: • an unrealized appreciation or depreciation of our contracted commitments to purchase or sell when purchase or sale prices under the commitments are compared with current commodity prices; • market values of natural gas and uranium inventories that differ from the cost of those commodities in inventory; • actual cash outlays for the purchase of these commodities that differ from anticipated cash outlays; and • actual off-system sales revenues that differ from anticipated revenues. The derivatives that we use to hedge these risks are governed by our risk management policies for forward contracts, futures, options, and swaps. Our net positions are continually assessed within our structured hedging programs to determine whether new or offsetting transactions are required. The goal of the hedging program is generally to mitigate financial risks while ensuring that sufficient volumes are available to meet our requirements. Contracts we enter into as part of our risk management program may be settled financially, settled by physical delivery, or net settled with the counterparty.
Noncontrolling Interests	Noncontrolling Interests As of December 31, 2021 and 2020, Ameren’s noncontrolling interests included the preferred stock of Ameren Missouri and Ameren Illinois.
Excise Taxes	Excise TaxesAmeren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes, that are levied on the sale or distribution of natural gas and electricity.
Earnings Per Share, Policy	Earnings per ShareEarnings per basic and diluted share are computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of basic and diluted common shares outstanding, respectively, during the applicable period. The weighted-average shares outstanding for earnings per diluted share includes the incremental effects resulting from performance share units, restricted stock units, and forward sale agreements relating to common stock when the impact would be dilutive, as calculated using the treasury stock method.

Rate And Regulatory Matters (Ta

Rate And Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2021
Public Utilities, General Disclosures [Abstract]
Schedule of Regulatory Frameworks and Significant Recovery Mechanisms	The following table presents the regulatory frameworks and significant regulatory recovery mechanisms for each of Ameren’s rate-regulated businesses, which are discussed in more detail below: Ameren Missouri Ameren Illinois’ electric distribution business Ameren Illinois’ natural gas delivery service business Ameren Illinois’ and ATXI’s electric transmission business Regulatory framework • Historical test year ratemaking • Natural gas revenues for residential customers adjusted for sales volume deviations resulting from weather through the WNAR • Performance-based formula ratemaking • Initial rates based on historical test year and expected net plant additions for the year before rates become effective • Revenues decoupled from sales volumes • Future test year ratemaking • Revenues for residential and small nonresidential customers decoupled from sales volumes through the VBA • Formula ratemaking • Initial rates based on future test year • Revenues decoupled from sales volumes Regulatory mechanisms • PISA Riders: • RESRAM • FAC • MEEIA • PGA • WNAR Trackers: • Pension and postretirement benefit costs • Certain excess deferred income taxes • Renewable energy standard costs • Electric distribution service and energy-efficiency revenue requirement reconciliation adjustments Riders: • Power procurement • Transmission services • Renewable energy credit compliance • Zero emission credits • Certain environmental costs • Bad debt write-offs • Costs of certain asbestos-related claims Riders: • QIP • PGA • VBA • Energy-efficiency program costs • Certain environmental costs • Bad debt write-offs • Invested capital taxes • Revenue requirement reconciliation adjustment
Schedule Of Regulatory Assets And Liabilities	The following table presents our regulatory assets and regulatory liabilities at December 31, 2021 and 2020: 2021 2020 Ameren Ameren Ameren Ameren Ameren Ameren Regulatory assets: Under-recovered FAC (a) $ 47 $ — $ 47 $ 48 $ — $ 48 Under-recovered PGA (b)(c) 49 114 163 — 2 2 MTM derivative losses (d) 77 125 202 21 200 221 IEIMA revenue requirement reconciliation adjustment (e)(f) — 42 42 — — — FERC revenue requirement reconciliation adjustment (g) — 18 43 — 28 50 Under-recovered VBA (h) — 17 17 — 11 11 Income taxes (i) 115 69 185 117 65 183 Bad debt rider (j) — 8 8 — 11 11 Callaway refueling and maintenance outage costs (k) 14 — 14 39 — 39 Unamortized loss on reacquired debt (l) 50 13 63 52 22 74 Environmental cost riders (m) — 70 70 — 93 93 Storm costs (f)(n) — 17 17 — 7 7 Allowance for funds used during construction for pollution control equipment (f)(o) 13 — 13 15 — 15 Customer generation rebate program (f)(p) — 47 47 — 17 17 PISA (f)(q) 244 — 244 78 — 78 FEJA energy-efficiency rider (f)(r) — 350 350 — 283 283 Other 41 42 83 37 40 77 Total regulatory assets $ 650 $ 932 $ 1,608 $ 407 $ 779 $ 1,209 Less: current regulatory assets (127) (180) (319) (60) (37) (109) Noncurrent regulatory assets $ 523 $ 752 $ 1,289 $ 347 $ 742 $ 1,100 Regulatory liabilities: Over-recovered FAC (a) $ 19 $ — $ 19 $ 10 $ — $ 10 Over-recovered Illinois electric power costs (b) — 13 13 — 15 15 Over-recovered PGA (b) — 1 1 7 15 22 MTM derivative gains (d) 50 41 91 11 10 21 IEIMA revenue requirement reconciliation adjustment (e) — — — — 22 22 FERC revenue requirement reconciliation adjustment (g) — 2 4 — 21 21 Income taxes (i) 1,208 770 2,066 1,317 790 2,192 Cost of removal (s) 1,028 929 1,988 1,027 873 1,923 AROs (t) 603 — 603 436 — 436 Bad debt rider (j) — 19 19 — 5 5 Pension and postretirement benefit costs (u) 399 392 791 198 177 375 Pension and postretirement benefit costs tracker (v) 28 — 28 55 — 55 Renewable energy credits and zero emission credits (w) — 246 246 — 200 200 RESRAM (x) 19 — 19 2 — 2 Excess income taxes collected in 2018 (y) 25 — 25 45 — 45 Other 32 15 48 28 23 59 Total regulatory liabilities $ 3,411 $ 2,428 $ 5,961 $ 3,136 $ 2,151 $ 5,403 Less: current regulatory liabilities (57) (54) (113) (26) (88) $ (121) Noncurrent regulatory liabilities $ 3,354 $ 2,374 $ 5,848 $ 3,110 $ 2,063 $ 5,282 (a) Under-recovered or over-recovered fuel costs to be recovered or refunded through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from, or refund to, customers that occurs over the next eight months. (b) Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral. (c) As a result of the significant increase in customer demand and prices for natural gas and electricity experienced in mid-February 2021 due to extremely cold weather, for the month of February 2021, Ameren Missouri and Ameren Illinois had under-recovered costs under their PGA clauses of $53 million and $221 million, respectively. Pursuant to an October 2021 MoPSC order, the collection period for Ameren Missouri’s cumulative PGA under-recovery as of August 2021, which includes the February 2021 under-recovery, was extended from 12 months to 36 months, beginning November 2021. Ameren Illinois is collecting its February 2021 PGA under-recovery over 18 months beginning April 2021, but the collection of the remaining balance may be extended at Ameren Illinois’ election to lessen the impact on customer rates. (d) Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information. (e) The difference between Ameren Illinois’ electric distribution service annual revenue requirement calculated under the performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. Any under-recovery or over-recovery will be recovered from, or refunded to, customers with interest within two years. (f) These assets earn a return at the applicable WACC. (g) Ameren Illinois’ and ATXI’s annual revenue requirement reconciliation calculated pursuant to the FERC’s electric transmission formula ratemaking framework. Any under-recovery or over-recovery will be recovered from, or refunded to, customers within two years. (h) Under-recovered natural gas revenue caused by sales volume deviations from weather normalized sales approved by the ICC in rate regulatory reviews. Each year’s amount will be recovered from customers from April through December of the following year. (i) The regulatory assets represent amounts that will be recovered from customers for deferred income taxes related to the equity component of allowance for funds used during construction and the effects of tax rate increases. The regulatory liabilities represent amounts that will be refunded to customers for deferred income taxes related to depreciation differences, other tax liabilities, and the unamortized portion of investment tax credits recorded at rates in excess of current statutory rates. Amounts associated with the equity component of allowance for funds used during construction and the unamortized portion of investment tax credits will be amortized over the expected life of the related assets. For net regulatory liabilities related to deferred income taxes recorded at rates other than the current statutory rate, the weighted-average remaining amortization periods at Ameren, Ameren Missouri, and Ameren Illinois are 35, 28, and 42 years. (j) A rider for the difference between the level of bad debt write-offs, net of any subsequent recoveries, incurred by Ameren Illinois and the level of such costs included in electric distribution and natural gas delivery service rates. Pursuant to a June 2020 ICC order, Ameren Illinois’ electric distribution bad debt rider provided for the recovery of bad debt expense in 2020. The under-recovery or over-recovery for each year is recovered from, or refunded to, customers over a twelve-month period beginning June the following year. (k) Maintenance expenses related to scheduled refueling and maintenance outages at Ameren Missouri’s Callaway Energy Center. Amounts are amortized over the period between refueling and maintenance outages, which has historically been approximately 18 months. (l) Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued. (m) The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 14 – Commitments and Contingencies for additional information. (n) Storm costs from 2018, 2020, and 2021 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred. (o) The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux Energy Center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux Energy Center through 2028. (p) Costs associated with Ameren Illinois’ customer generation rebate program. Costs are amortized over a 15-year period, beginning in the year rebates are paid. (q) Under the PISA, Ameren Missouri is permitted to defer and recover 85% of the depreciation expense and earn a return at the applicable WACC on investments in certain property, plant, and equipment placed in service and not included in base rates. Accumulated PISA deferrals are added to rate base prospectively and amortized over a period of 20 years following a regulatory rate review. (r) The electric energy-efficiency investments are being amortized over their weighted-average useful lives beginning in the period in which they were made, with current remaining amortization periods ranging from 5 to 13 years. (s) Estimated funds collected from customers to pay for the future removal cost of property, plant, and equipment retired from service, net of salvage. (t) The ARO regulatory liability includes the nuclear decommissioning trust fund balance ($1,159 million and $982 million at December 31, 2021 and 2020, respectively), net of recoverable removal costs for AROs ($556 million and $546 million at December 31, 2021 and 2020, respectively). See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations. (u) Over-recovered costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 10 – Retirement Benefits for additional information. (v) A regulatory recovery mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri and the level of such costs included in customer rates. The period of refund varies based on MoPSC approval in a regulatory rate review. The weighted-average remaining amortization period is five years. (w) Funds collected for the purchase of renewable energy credits and zero emission credits through IPA procurements. The balance will be amortized as the credits are purchased. (x) Over-recovered costs associated with Ameren Missouri’s compliance with the state of Missouri’s renewable energy standard. Under-recovered or over-recovered costs are aggregated over a twelve-month period beginning each August and are amortized over a twelve-month period beginning February the following year. (y) The excess amount collected in rates related to the TCJA from January 1, 2018, through July 31, 2018. The regulatory liability is being amortized over a three-year period, which began in April 2020.

Property And Plant, Net (Tables

Property And Plant, Net (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Schedule Of Property And Plant, Net	The following table presents components of “Property, plant, and equipment, net” at December 31, 2021 and 2020: Ameren Ameren Other Ameren 2021 Property, plant, and equipment at original cost: (a) Electric generation: Coal (b)(c) $ 3,955 $ — $ — $ 3,955 Natural gas 1,105 — — 1,105 Nuclear 5,615 — — 5,615 Renewable (d) 1,889 — — 1,889 Electric distribution 7,286 7,017 — 14,303 Electric transmission 1,628 4,105 1,800 7,533 Natural gas 607 3,586 — 4,193 Other (e) 1,584 1,183 242 3,009 23,669 15,891 2,042 41,602 Less: Accumulated depreciation and amortization 9,784 4,100 330 14,214 13,885 11,791 1,712 27,388 Construction work in progress: Nuclear fuel in process 133 — — 133 Other 674 432 30 1,136 Plant to be abandoned, net (f) 604 — — 604 Property, plant, and equipment, net $ 15,296 $ 12,223 $ 1,742 $ 29,261 2020 Property, plant, and equipment at original cost: (a) Electric generation: Coal (b)(c) $ 4,875 $ — $ — $ 4,875 Natural gas 1,097 — — 1,097 Nuclear 5,608 — — 5,608 Renewable (d) 1,301 — — 1,301 Electric distribution 6,784 6,649 — 13,433 Electric transmission 1,482 3,575 1,774 6,831 Natural gas 561 3,308 — 3,869 Other (e) 1,390 1,070 245 2,705 23,098 14,602 2,019 39,719 Less: Accumulated depreciation and amortization 9,689 3,780 304 13,773 13,409 10,822 1,715 25,946 Construction work in progress: Nuclear fuel in process 75 — — 75 Other 395 379 12 786 Property, plant, and equipment, net $ 13,879 $ 11,201 $ 1,727 $ 26,807 (a) The estimated lives for each asset group are as follows: 5 to 72 years for electric generation, excluding Ameren Missouri’s hydroelectric generating assets, which have useful lives of up to 150 years; 20 to 80 years for electric distribution; 50 to 75 years for electric transmission; 20 to 80 years for natural gas; and 2 to 55 years for other. (b) Includes $29 million and $36 million of oil-fired generation at December 31, 2021 and 2020, respectively. (c) Original cost amounts include two CTs that have related financing obligations. The gross cumulative asset value of those agreements was $243 million and $240 million at December 31, 2021 and 2020, respectively. The total accumulated depreciation associated with the two CTs was $105 million and $99 million at December 31, 2021 and 2020, respectively. See Note 5 – Long-term Debt and Equity Financings for additional information on these agreements. (d) Renewable includes hydroelectric, wind, solar, and methane gas generation facilities. (e) Other property, plant, and equipment includes assets used to support electric and natural gas services. (f) Represents the net book value of the Rush Island Energy Center and related construction work in progress as Ameren Missouri expects to retire the energy center significantly in advance of its previously expected useful life and in the near term. See Plant to be Abandoned, Net under Note 1 – Summary of Significant Accounting Policies and NSR and Clean Air Act Litigation under Note 14 – Commitments and Contingencies for additional information on the planned accelerated retirement of the Rush Island Energy Center.
Schedule of Capitalized Software	Capitalized software costs are classified within “Property, Plant, and Equipment, Net” on the balance sheet and are amortized on a straight-line basis over the expected period of benefit, ranging from 2 to 15 years. The following table presents the amortization, gross carrying value, and related accumulated amortization of capitalized software by year: Amortization Expense Gross Carrying Value Accumulated Amortization 2021 2020 2019 2021 2020 2021 2020 Ameren $ 125 $ 93 $ 78 $ 1,199 $ 1,021 $ (757) $ (640) Ameren Missouri 66 44 30 523 398 (255) (189) Ameren Illinois 53 45 45 452 397 (291) (238)
Schedule of Capitalized Software, Future Amortization Expense	Annual amortization expense for capitalized software placed in service as of December 31, 2021, is estimated to be as follows: 2022 2023 2024 2025 2026 Ameren $ 135 $ 119 $ 87 $ 47 $ 21 Ameren Missouri 75 69 54 31 14 Ameren Illinois 56 47 31 14 6

Short-Term Debt And Liquidity (

Short-Term Debt And Liquidity (Tables)	12 Months Ended
	Dec. 31, 2021
Line of Credit Facility [Abstract]
Schedule Of Maximum Aggregate Amount Available On Credit Agreements	The following table presents the maximum aggregate amount available to each borrower under each facility: Missouri Illinois Ameren (parent) $ 900 $ 500 Ameren Missouri 850 (a) Ameren Illinois (a) 800 (a) Not applicable.
Schedule of Commercial Paper	The following table summarizes the activity and relevant interest rates for Ameren (parent)’s, Ameren Missouri’s, and Ameren Illinois’ commercial paper issuances and borrowings under the Credit Agreements in the aggregate for the years ended December 31, 2021 and 2020: Ameren (parent) Ameren Missouri Ameren Illinois Ameren Consolidated 2021 Average daily amount outstanding $ 387 $ 99 $ 118 $ 604 Commercial paper issuances outstanding at period-end 277 165 103 545 Weighted-average interest rate 0.22 % 0.22 % 0.21 % 0.22 % Peak amount outstanding during period (a) $ 650 $ 546 $ 485 $ 1,134 Peak interest rate 0.38 % 0.35 % 0.35 % 0.38 % 2020 Average daily amount outstanding $ 108 $ 109 $ 46 $ 263 Commercial paper issuances outstanding at period-end 490 — — 490 Weighted-average interest rate 1.04 % 1.73 % 0.97 % 1.31 % Peak amount outstanding during period (a) $ 490 $ 573 $ 250 $ 908 Peak interest rate 3.30 % 5.05 % (b) 3.40 % 5.05 % (b) (a) The timing of peak outstanding commercial paper issuances and borrowings under the Credit Agreements varies by company. Therefore, the sum of individual company peak amounts may not equal the Ameren consolidated peak amount for the period. (b) Ameren’s and Ameren Missouri’s peak interest rates were affected by temporary disruptions in the commercial paper market in the first quarter of 2020.

Long-Term Debt And Equity Fin_2

Long-Term Debt And Equity Financings (Tables)	12 Months Ended
	Dec. 31, 2021
Debt Instrument [Line Items]
Schedule of Long-term Debt Instruments	The following table presents long-term debt outstanding, including maturities due within one year, as of December 31, 2021 and 2020: 2021 2020 Ameren (Parent): 2.50% Senior unsecured notes due 2024 $ 450 $ 450 3.65% Senior unsecured notes due 2026 350 350 1.95% Senior unsecured notes due 2027 500 — 1.75% Senior unsecured notes due 2028 450 — 3.50% Senior unsecured notes due 2031 800 800 Total long-term debt, gross 2,550 1,600 Less: Unamortized discount and premium (2) (2) Less: Unamortized debt issuance costs (15) (10) Long-term debt, net $ 2,533 $ 1,588 Ameren Missouri: Bonds and notes: 1.60% 1992 Series bonds due 2022 (a) $ 47 $ 47 3.50% Senior secured notes due 2024 (b) 350 350 2.95% Senior secured notes due 2027 (b) 400 400 3.50% First mortgage bonds due 2029 (d) 450 450 2.95% First mortgage bonds due 2030 (d) 465 465 2.15% First mortgage bonds due 2032 (d) 525 — 2.90% 1998 Series A bonds due 2033 (a) 60 60 2.90% 1998 Series B bonds due 2033 (a) 50 50 2.75% 1998 Series C bonds due 2033 (a) 50 50 5.50% Senior secured notes due 2034 (b) 184 184 5.30% Senior secured notes due 2037 (b) 300 300 8.45% Senior secured notes due 2039 (b)(c) 350 350 3.90% Senior secured notes due 2042 (b)(c) 485 485 3.65% Senior secured notes due 2045 (b) 400 400 4.00% First mortgage bonds due 2048 (d) 425 425 3.25% First mortgage bonds due 2049 (d) 330 330 2.625% First mortgage bonds due 2051 (d) 550 550 Finance obligations: City of Bowling Green agreement (Peno Creek CT) due 2022 (e) 8 16 Audrain County agreement (Audrain County CT) due 2023 (e) 240 240 Total long-term debt, gross 5,669 5,152 Less: Unamortized discount and premium (12) (12) Less: Unamortized debt issuance costs (38) (36) Less: Maturities due within one year (55) (8) Long-term debt, net $ 5,564 $ 5,096 2021 2020 Ameren Illinois: Bonds and notes: 2.70% Senior secured notes due 2022 (f)(g) $ 400 $ 400 0.375% First mortgage bonds due 2023 (h) 100 — 3.25% Senior secured notes due 2025 (f) 300 300 6.125% Senior secured notes due 2028 (f) 60 60 3.80% First mortgage bonds due 2028 (h) 430 430 1.55% First mortgage bonds due 2030 (h) 375 375 6.70% Senior secured notes due 2036 (f) 61 61 6.70% Senior secured notes due 2036 (f) 42 42 4.80% Senior secured notes due 2043 (f) 280 280 4.30% Senior secured notes due 2044 (f) 250 250 4.15% Senior secured notes due 2046 (f) 490 490 3.70% First mortgage bonds due 2047 (h) 500 500 4.50% First mortgage bonds due 2049 (h) 500 500 3.25% First mortgage bonds due 2050 (h) 300 300 2.90% First mortgage bonds due 2051 (h) 350 — Total long-term debt, gross 4,438 3,988 Less: Unamortized discount and premium (7) (6) Less: Unamortized debt issuance costs (39) (36) Less: Maturities due within one year (400) — Long-term debt, net $ 3,992 $ 3,946 ATXI: 2.45% Senior unsecured notes due 2036 (i) $ 75 $ — 3.43% Senior unsecured notes due 2050 (j) 450 450 Total long-term debt, gross 525 450 Less: Unamortized debt issuance costs (2) (2) Less: Maturities due within one year (50) — Long-term debt, net $ 473 $ 448 Ameren consolidated long-term debt, net $ 12,562 $ 11,078 (a) These bonds are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture and have a fall-away lien provision similar to that of Ameren Missouri’s senior secured notes. (b) These notes are collaterally secured by first mortgage bonds issued by Ameren Missouri under the Ameren Missouri mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under the Ameren Missouri mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the 2051 maturity of the 2.625% first mortgage bonds and the restrictions preventing a release date to occur that are attached to certain senior secured notes described in footnote (c) below, Ameren Missouri does not expect the first mortgage lien protection associated with these notes to fall away. (c) Ameren Missouri has agreed that so long as any of the 3.90% senior secured notes due 2042 are outstanding, Ameren Missouri will not permit a release date to occur, and so long as any of the 8.45% senior secured notes due 2039 are outstanding, Ameren Missouri will not optionally redeem, purchase, or otherwise retire in full the outstanding first mortgage bonds not subject to release provisions. (d) These bonds are first mortgage bonds issued by Ameren Missouri under the Ameren Missouri bond indenture. They are secured by substantially all Ameren Missouri property and franchises. (e) Payments due related to these financing obligations are paid to a trustee, which is authorized to utilize the cash only to pay equal amounts due to Ameren Missouri under related bonds issued by the city/county and held by Ameren Missouri. The timing and amounts of payments due from Ameren Missouri under the agreements are equal to the timing and amount of bond service payments due to Ameren Missouri, resulting in no net cash flow. The balance of both the financing obligations and the related investments in debt securities, recorded in “Other Assets,” was $248 million and $256 million, respectively, as of December 31, 2021 and 2020. (f) These notes are collaterally secured by first mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. The notes have a fall-away lien provision and will remain secured only as long as any first mortgage bonds issued under its mortgage indenture remain outstanding. Redemption, purchase, or maturity of all first mortgage bonds, including first mortgage bonds currently outstanding and any that may be issued in the future, would result in a release of the first mortgage bonds currently securing these notes, at which time these notes would become unsecured obligations. Considering the 2051 maturity date of the 2.90% first mortgage bonds, Ameren Illinois does not expect the first mortgage lien protection associated with these notes to fall away. (g) Ameren Illinois has agreed that so long as any of the 2.70% senior secured notes due 2022 are outstanding, Ameren Illinois will not permit a release date to occur. (h) These bonds are first mortgage bonds issued by Ameren Illinois under the Ameren Illinois mortgage indenture. They are secured by substantially all Ameren Illinois property and franchises.
Schedule Of Maturities Of Long-Term Debt	The following table presents the principal maturities schedule for the 2.45% senior unsecured notes due 2036: Payment Date Principal Payment November 2029 $ 30 November 2036 45 Total $ 75 (j) The following table presents the principal maturities schedule for the 3.43% senior unsecured notes due 2050: Payment Date Principal Payment August 2022 $ 49.5 August 2024 49.5 August 2027 49.5 August 2030 49.5 August 2032 49.5 August 2038 49.5 August 2043 76.5 August 2050 76.5 Total $ 450.0 The following table presents the aggregate maturities of long-term debt, including current maturities, at December 31, 2021: Ameren (parent) (a) Ameren Missouri (a) Ameren Illinois (a) ATXI (a) Ameren Consolidated (a) 2022 $ — $ 55 $ 400 $ 50 $ 505 2023 — 240 100 — 340 2024 450 350 — 50 850 2025 — — 300 — 300 2026 350 — — — 350 Thereafter 1,750 5,024 3,638 425 10,837 Total $ 2,550 $ 5,669 $ 4,438 $ 525 $ 13,182 (a) Excludes unamortized discount, premium, and debt issuance costs of $17 million, $50 million, $46 million, and $2 million at Ameren (parent), Ameren Missouri, Ameren Illinois, and ATXI, respectively.
Schedule Of Outstanding Preferred Stock	The following table presents the outstanding preferred stock of Ameren Missouri and Ameren Illinois, which is redeemable at the option of the issuer, at the prices shown below as of December 31, 2021 and 2020: Shares Outstanding Redemption Price (per share) 2021 2020 Ameren Missouri: Without par value and stated value of $100 per share, 25 million shares authorized $3.50 Series 130,000 shares $ 110.00 $ 13 $ 13 $3.70 Series 40,000 shares 104.75 4 4 $4.00 Series 150,000 shares 105.625 15 15 $4.30 Series 40,000 shares 105.00 4 4 $4.50 Series 213,595 shares 110.00 (a) 21 21 $4.56 Series 200,000 shares 102.47 20 20 $4.75 Series 20,000 shares 102.176 2 2 $5.50 Series A 14,000 shares 110.00 1 1 Total $ 80 $ 80 Ameren Illinois: With par value of $100 per share, 2 million shares authorized 4.00% Series 144,275 shares $ 101.00 $ 14 $ 14 4.08% Series 45,224 shares 103.00 5 5 4.20% Series 23,655 shares 104.00 2 2 4.25% Series 50,000 shares 102.00 5 5 4.26% Series 16,621 shares 103.00 2 2 4.42% Series 16,190 shares 103.00 2 2 4.70% Series 18,429 shares 104.30 2 2 4.90% Series 73,825 shares 102.00 7 7 4.92% Series 49,289 shares 103.50 5 5 5.16% Series 50,000 shares 102.00 5 5 6.625% Series (b) 100.00 — 12 7.75% Series (b) 100.00 — 1 Total $ 49 $ 62 Total Ameren $ 129 $ 142 (a) In the event of voluntary liquidation, $105.50. (b) In March 2021, Ameren Illinois redeemed its 6.625% and 7.75% series preferred stock at par.
Schedule of Required and Actual Debt Ratios	The following table summarizes the required and actual interest coverage ratios for interest charges, dividend coverage ratios, and bonds and preferred stock issuable as of December 31, 2021, at an assumed interest rate of 5% and dividend rate of 6%. Required Interest Coverage Ratio (a) Actual Interest Bonds Issuable (b) Required Dividend Coverage Ratio (c) Actual Dividend Preferred Stock Ameren Missouri > 2.0 3.2 $4,834 > 2.5 152.4 $3,418 Ameren Illinois > 2.0 7.3 7,697 > 1.5 3.5 203 (d) (a) Coverage required on the annual interest charges on first mortgage bonds outstanding and to be issued. Coverage is not required in certain cases when additional first mortgage bonds are issued on the basis of retired bonds. (b) Amount of bonds issuable based either on required coverage ratios or unfunded property additions, whichever is more restrictive. The amounts shown also include bonds issuable based on retired bond capacity of $2,437 million and $643 million at Ameren Missouri and Ameren Illinois, respectively. (c) Coverage required on the annual dividend on preferred stock outstanding and to be issued, as required in the respective company’s articles of incorporation. (d) Preferred stock issuable is restricted by the amount of preferred stock that is currently authorized by Ameren Illinois’ articles of incorporation.

Other Income, Net (Tables)

Other Income, Net (Tables)	12 Months Ended
	Dec. 31, 2021
Other Nonoperating Income (Expense) [Abstract]
Other Income And Expenses	The following table presents the components of “Other Income, Net” in the Ameren Companies’ statements of income for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren: Other Income, Net Allowance for equity funds used during construction $ 43 $ 32 $ 28 Interest income on industrial development revenue bonds 25 25 25 Other interest income 2 4 8 Non-service cost components of net periodic benefit income (a) 136 116 90 Miscellaneous income 22 13 6 Donations (9) (25) (b) (12) Miscellaneous expense (17) (14) (15) Total Other Income, Net $ 202 $ 151 $ 130 Ameren Missouri: Other Income, Net Allowance for equity funds used during construction $ 26 $ 19 $ 19 Interest income on industrial development revenue bonds 25 25 25 Other interest income 1 1 1 Non-service cost components of net periodic benefit income (a) 55 46 18 Miscellaneous income 3 4 5 Donations (4) (12) (b) (3) Miscellaneous expense (7) (7) (7) Total Other Income, Net $ 99 $ 76 $ 58 2021 2020 2019 Ameren Illinois: Other Income, Net Allowance for equity funds used during construction $ 17 $ 13 $ 9 Interest income 1 3 6 Non-service cost components of net periodic benefit income (a) 55 48 47 Miscellaneous income 6 6 3 Donations (5) (5) (5) Miscellaneous expense (8) (6) (7) Total Other Income, Net $ 66 $ 59 $ 53 (a) For the years ended December 31, 2021, 2020, and 2019, the non-service cost components of net periodic benefit income were adjusted by amounts deferred of $(7) million, $(4) million, and $29 million, respectively, due to a tracker for the difference between the level of such costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. (b) Includes $8 million pursuant to Ameren Missouri’s March 2020 electric rate order. The following table presents the components of “Total Other Expense, Net” in the Condensed Statement of Income and Comprehensive Income for the years ended December 31, 2021, 2020, and 2019: (In millions) 2021 2020 2019 Total Other Expense, Net Non-service cost components of net periodic benefit income $ 1 $ 1 $ 2 Donations — (8) (3) Other expense, net (1) (1) (1) Total Other Expense, Net $ — $ (8) $ (2)

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Open Gross Derivative Volumes By Commodity Type	The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2021 and 2020. As of December 31, 2021, these contracts extended through October 2024, October 2026, May 2032, and March 2024 for fuel oils, natural gas, power, and uranium, respectively. Quantity (in millions, except as indicated) 2021 2020 Commodity Ameren Missouri Ameren Ameren Ameren Missouri Ameren Ameren Fuel oils (in gallons) 30 — 30 43 — 43 Natural gas (in mmbtu) 35 144 179 33 114 147 Power (in MWhs) 6 6 12 6 7 13 Uranium (pounds in thousands) 586 — 586 365 — 365
Derivative Instruments Carrying Value	The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of December 31, 2021 and 2020: 2021 2020 Commodity Balance Sheet Location Ameren Ameren Ameren Ameren Ameren Ameren Fuel oils Other current assets $ 8 $ — $ 8 $ 2 $ — $ 2 Other assets 5 — 5 — — — Natural gas Other current assets 7 28 35 1 8 9 Other assets 5 13 18 2 2 4 Power Other current assets 23 — 23 7 — 7 Uranium Other assets 1 — 1 — — — Total assets $ 49 $ 41 $ 90 $ 12 $ 10 $ 22 Fuel oils Other current liabilities $ — $ — $ — $ 7 $ — $ 7 Other deferred credits and liabilities — — — 2 — 2 Natural gas Other current liabilities 2 6 8 1 1 2 Other deferred credits and liabilities 1 2 3 — 1 1 Power Other current liabilities 50 9 59 3 17 20 Other deferred credits and liabilities 23 108 131 8 181 189 Uranium Other current liabilities 1 — 1 — — — Total liabilities $ 77 $ 125 $ 202 $ 21 $ 200 $ 221
Offsetting Assets and Liabilities	The following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of December 31, 2021. If the gross amounts recognized on the balance sheet were netted with derivative instruments and cash collateral received or posted at December 31, 2020, the net amounts would not be materially different from the gross amounts. Gross Amounts Not Offset in the Balance Sheet Commodity Contracts Eligible to be Offset Gross Amounts Recognized in the Balance Sheet Derivative Instruments Cash Collateral Received/Posted (a) Net 2021 Assets: Ameren Missouri $ 49 $ 15 $ — $ 34 Ameren Illinois 41 4 — 37 Ameren $ 90 $ 19 $ — $ 71 Liabilities: Ameren Missouri $ 77 $ 15 $ 47 $ 15 Ameren Illinois 125 4 — 121 Ameren $ 202 $ 19 $ 47 $ 136 (a) Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” on Ameren’s balance sheet and in “Current collateral assets” on Ameren Missouri’s balance sheet.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis	The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets: Ameren Missouri Derivative assets – commodity contracts: Fuel oils $ 13 $ — $ — $ 13 $ — $ — $ 2 $ 2 Natural gas — 12 — 12 — 3 — 3 Power 10 — 13 23 2 — 5 7 Uranium — — 1 1 — — — — Total derivative assets – commodity contracts $ 23 $ 12 $ 14 $ 49 $ 2 $ 3 $ 7 $ 12 Nuclear decommissioning trust fund: Equity securities: U.S. large capitalization $ 824 $ — $ — $ 824 $ 680 $ — $ — $ 680 Debt securities: U.S. Treasury and agency securities — 141 — 141 — 115 — 115 Corporate bonds — 131 — 131 — 115 — 115 Other — 56 — 56 — 67 — 67 Total nuclear decommissioning trust fund $ 824 $ 328 $ — $ 1,152 (a) $ 680 $ 297 $ — $ 977 (a) Total Ameren Missouri $ 847 $ 340 $ 14 $ 1,201 $ 682 $ 300 $ 7 $ 989 Ameren Illinois Derivative assets – commodity contracts: Natural gas $ 1 $ 33 $ 7 $ 41 $ — $ 6 $ 4 $ 10 Ameren Derivative assets – commodity contracts (b) $ 24 $ 45 $ 21 $ 90 $ 2 $ 9 $ 11 $ 22 Nuclear decommissioning trust fund (c) 824 328 — 1,152 (a) 680 297 — 977 (a) Total Ameren $ 848 $ 373 $ 21 $ 1,242 $ 682 $ 306 $ 11 $ 999 Liabilities: Ameren Missouri Derivative liabilities – commodity contracts: Fuel oils $ — $ — $ — $ — $ 6 $ — $ 3 $ 9 Natural gas — 2 1 3 — 1 — 1 Power 45 — 28 73 8 — 3 11 Uranium — — 1 1 — — — — Total Ameren Missouri $ 45 $ 2 $ 30 $ 77 $ 14 $ 1 $ 6 $ 21 Ameren Illinois Derivative liabilities – commodity contracts: Natural gas $ — $ 5 $ 3 $ 8 $ — $ 1 $ 1 $ 2 Power — — 117 117 — — 198 198 Total Ameren Illinois $ — $ 5 $ 120 $ 125 $ — $ 1 $ 199 $ 200 Ameren Derivative liabilities – commodity contracts (b) $ 45 $ 7 $ 150 $ 202 $ 14 $ 2 $ 205 $ 221 (a) Balance excludes $7 million and $5 million of cash and cash equivalents, receivables, payables, and accrued income, net for December 31, 2021 and 2020, respectively. (b) See the Ameren Missouri and Ameren Illinois sections of the table for a breakout of the fair value of Ameren’s derivative assets and liabilities by type of commodity. (c) See the Ameren Missouri section of the table for a breakout of Ameren’s nuclear decommissioning trust fund by investment type.
Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy	The following table presents the fair value reconciliation of Level 3 power derivative contract assets and liabilities measured at fair value on a recurring basis for the years ended December 31, 2021 and 2020: 2021 2020 Ameren Ameren Ameren Ameren Ameren Ameren Beginning balance at January 1 $ 2 $ (198) $ (196) $ 13 $ (224) $ (211) Realized and unrealized gains (losses) included in regulatory assets/liabilities (1) 70 69 15 8 23 Settlements (16) 11 (5) (26) 18 (8) Ending balance at December 31 $ (15) $ (117) $ (132) $ 2 $ (198) $ (196) Change in unrealized gains (losses) related to assets/liabilities held at December 31 $ (14) $ 65 $ 51 $ 1 $ 9 $ 10
Fair Value Inputs, Assets and Liabilities, Quantitative Information	The following table describes the valuation techniques and significant unobservable inputs utilized for the fair value of our Level 3 power derivative contract assets and liabilities as of December 31, 2021 and 2020: Fair Value Weighted Average (b) Commodity Assets Liabilities Valuation Technique(s) Unobservable Input (a) Range 2021 Power (c) $ 13 $ (145) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 32 – 55 40 Nodal basis ($/MWh) (14) – 0 (2) Trend rate (%) 0 – 0 0 2020 Power (c) $ 5 $ (201) Discounted cash flow Average forward peak and off-peak pricing – forwards/swaps ($/MWh) 23 – 37 29 Nodal basis ($/MWh) (6) – 0 (2) Trend rate (%) 2 – 6 3 (a) Generally, significant increases (decreases) in these inputs in isolation would result in a significantly higher (lower) fair value measurement. (b) Unobservable inputs were weighted by relative fair value. (c) Valuations through 2029 use visible forward prices adjusted for nodal-to-hub basis differentials. Valuations beyond 2029 use a trend rate factor and are similarly adjusted for nodal-to-hub basis differentials.
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block]	The following table sets forth, by level within the fair value hierarchy, the carrying amount and fair value of financial assets and liabilities disclosed, but not carried, at fair value as of December 31, 2021 and 2020: Carrying Fair Value Level 1 Level 2 Level 3 Total December 31, 2021 Ameren: Cash, cash equivalents, and restricted cash $ 155 $ 155 $ — $ — $ 155 Investments in industrial development revenue bonds (a) 248 — 248 — 248 Short-term debt 545 — 545 — 545 Long-term debt (including current portion) (a) 13,067 (b) — 13,930 591 (c) 14,521 Ameren Missouri: Cash, cash equivalents, and restricted cash $ 8 $ 8 $ — $ — $ 8 Investments in industrial development revenue bonds (a) 248 — 248 — 248 Short-term debt 165 — 165 — 165 Long-term debt (including current portion) (a) 5,619 (b) — 6,321 — 6,321 Ameren Illinois: Cash, cash equivalents, and restricted cash $ 133 $ 133 $ — $ — $ 133 Short-term debt 103 — 103 — 103 Long-term debt (including current portion) 4,392 (b) — 4,971 — 4,971 December 31, 2020 Ameren: Cash, cash equivalents, and restricted cash $ 301 $ 301 $ — $ — $ 301 Investments in industrial development revenue bonds (a) 256 — 256 — 256 Short-term debt 490 — 490 — 490 Long-term debt (including current portion) (a) 11,086 (b) — 12,778 537 (c) 13,315 Ameren Missouri: Cash, cash equivalents, and restricted cash $ 145 $ 145 $ — $ — $ 145 Advances to money pool 139 — 139 — 139 Investments in industrial development revenue bonds (a) 256 — 256 — 256 Long-term debt (including current portion) (a) 5,104 (b) — 6,160 — 6,160 Ameren Illinois: Cash, cash equivalents, and restricted cash $ 147 $ 147 $ — $ — $ 147 Borrowings from money pool 19 — 19 — 19 Long-term debt (including current portion) 3,946 (b) — 4,822 — 4,822 (a) Ameren and Ameren Missouri have investments in industrial development revenue bonds, classified as held-to-maturity and recorded in “Other Assets,” that are equal to the finance obligations for the Peno Creek and Audrain CT energy centers. As of December 31, 2021 and 2020, the carrying amount of both the investments in industrial development revenue bonds and the finance obligations approximated fair value. (b) Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $94 million, $38 million, and $39 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2021. Included unamortized debt issuance costs, which were excluded from the fair value measurement, of $84 million, $36 million, and $36 million for Ameren, Ameren Missouri, and Ameren Illinois, respectively, as of December 31, 2020. (c) The Level 3 fair value amount consists of ATXI’s senior unsecured notes.

Callaway Energy Center (Tables)

Callaway Energy Center (Tables)	12 Months Ended
	Dec. 31, 2021
Nuclear Waste Matters [Abstract]
Proceeds From Sale Of Investments In Nuclear Decommissioning Trust Fund And Gross Realized Gains And Losses	The following table presents proceeds from the sale and maturities of investments in Ameren Missouri’s nuclear decommissioning trust fund and the gross realized gains and losses resulting from those sales for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Proceeds from sales and maturities $ 439 $ 183 $ 260 Gross realized gains 32 10 10 Gross realized losses 6 3 2
Fair Value Of Securities In Nuclear Decommissioning Trust Fund	The following table presents the cost and fair value of investments in debt and equity securities in Ameren’s and Ameren Missouri’s nuclear decommissioning trust fund at December 31, 2021 and December 31, 2020: Security Type Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value 2021 Debt securities $ 320 $ 10 $ 2 $ 328 Equity securities 188 640 4 824 Cash and cash equivalents 4 — — 4 Other (a) 3 — — 3 Total $ 515 $ 650 $ 6 $ 1,159 2020 Debt securities $ 272 $ 25 $ — $ 297 Equity securities 198 491 9 680 Cash and cash equivalents 4 — — 4 Other (a) 1 — — 1 Total $ 475 $ 516 $ 9 $ 982 (a) Represents net receivables and payables relating to pending securities sales, interest, and securities purchases.
Fair Value Of Securities In Nuclear Decommissioning Trust Fund Classified by Contractual Maturity Date	The following table presents the costs and fair values of investments in debt securities in Ameren’s and Ameren Missouri’s nuclear decommissioning trust fund according to their contractual maturities at December 31, 2021: Cost Fair Value Less than 5 years $ 155 $ 156 5 years to 10 years 71 72 Due after 10 years 94 100 Total $ 320 $ 328
Schedule of Insurance Coverage	The following table presents insurance coverage at Ameren Missouri’s Callaway Energy Center at January 1, 2022: Type and Source of Coverage Most Recent Maximum Coverages Maximum Assessments Public liability and nuclear worker liability: American Nuclear Insurers January 1, 2022 $ 450 $ — Pool participation (a) 13,073 (a) 138 (b) $ 13,523 (c) $ 138 Property damage: NEIL and EMANI April 1, 2021 $ 3,200 (d) $ 25 (e) Accidental outage: NEIL April 1, 2021 $ 490 (f) $ 7 (e) (a) Provided through mandatory participation in an industrywide retrospective premium assessment program. The maximum coverage available is dependent on the number of United States commercial reactors participating in the program. (b) Retrospective premium under the Price-Anderson Act. This is subject to retrospective assessment with respect to a covered loss in excess of $450 million in the event of an incident at any licensed United States commercial reactor, payable at $21 million per year. (c) Limit of liability for each incident under the Price-Anderson liability provisions of the Atomic Energy Act of 1954, as amended. This limit is subject to change to account for the effects of inflation and changes in the number of licensed power reactors. (d) NEIL provides $2.7 billion in property damage, stabilization, decontamination, and premature decommissioning insurance for radiation events and $2.3 billion in property damage insurance for nonradiation events. EMANI provides $490 million in property damage insurance for both radiation and nonradiation events. (e) All NEIL-insured plants could be subject to assessments should losses exceed the accumulated funds from NEIL. (f) Accidental outage insurance provides for lost sales in the event of a prolonged accidental outage. Weekly indemnity up to $4.5 million for 52 weeks, which commences after the first 12 weeks of an outage, plus up to $3.6 million per week for a minimum of 71 weeks thereafter for a total not exceeding the policy limit of $490 million. Nonradiation events are limited to $328 million.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2021
Summary Of Benefit Liability Recorded	The following table presents the net benefit liability/(asset) recorded on the balance sheets as of December 31, 2021 and 2020: 2021 2020 Ameren (a) $ (717) $ (249) Ameren Missouri (a) (189) (25) Ameren Illinois (a) (416) (210) (a) Liabilities associated with pension and other postretirement benefits are recorded in “Other current liabilities” and “Other deferred credits and liabilities” on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets.
Funded Status Of Benefit Plans and Amounts Included In Regulatory Assets and AOCI	The following table presents the funded status of Ameren’s pension and postretirement benefit plans as of December 31, 2021 and December 31, 2020. It also provides the amounts included in regulatory assets or liabilities and accumulated OCI at December 31, 2021 and December 31, 2020, that have not been recognized in net periodic benefit costs. 2021 2020 Pension Postretirement Pension Postretirement Accumulated benefit obligation at end of year $ 5,174 $ (a) $ 5,213 $ (a) Change in benefit obligation: Net benefit obligation at beginning of year $ 5,510 $ 1,204 $ 4,967 $ 1,110 Service cost 134 23 110 19 Interest cost 152 33 174 39 Participant contributions — 9 — 8 Actuarial (gain) loss (82) (80) 508 91 Benefits paid (257) (60) (249) (63) Net benefit obligation at end of year 5,457 1,129 5,510 1,204 Change in plan assets: Fair value of plan assets at beginning of year 5,510 1,453 4,564 1,297 Actual return on plan assets 432 154 1,143 209 Employer contributions 60 2 52 2 Participant contributions — 9 — 8 Benefits paid (257) (60) (249) (63) Fair value of plan assets at end of year 5,745 1,558 5,510 1,453 Funded status – surplus (288) (429) — (249) Accrued benefit asset at December 31 $ (288) $ (429) $ — $ (249) Amounts recognized in the balance sheet consist of: Noncurrent asset $ (327) $ (429) $ (39) $ (249) Current liability (b) 2 — 2 — Noncurrent liability (c) 37 — 37 — Net asset recognized $ (288) $ (429) $ — $ (249) Amounts recognized in regulatory assets or liabilities consist of: Net actuarial gain $ (415) $ (343) $ (138) $ (200) Prior service credit — (33) — (37) Amounts recognized in accumulated OCI (pretax) consist of: Net actuarial (gain) loss (8) 1 5 6 Total $ (423) $ (375) $ (133) $ (231) (a) Not applicable. (b) Included in “Other current liabilities” on Ameren’s consolidated balance sheet. (c) Included in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.
Assumptions Used To Determine Benefit Obligations	The following table presents the assumptions used to determine our benefit obligations at December 31, 2021 and 2020: Pension Benefits Postretirement Benefits 2021 2020 2021 2020 Discount rate at measurement date 3.00 % 2.75 % 3.00 % 2.75 % Increase in future compensation 3.50 3.50 3.50 3.50 Cash balance pension plan interest crediting rate 5.00 5.00 (a) (a) Medical cost trend rate (initial) (b) (a) (a) 5.00 5.00 Medical cost trend rate (ultimate) (b) (a) (a) 5.00 5.00 (a) Not applicable. (b) Initial and ultimate medical cost trend rate for certain Medicare-eligible participants was 2.50% and 3.00% at December 31, 2021 and 2020, respectively.
Schedule Of Cash Contributions Made To Benefit Plans	The following table presents the cash contributions made to our defined benefit retirement plans and to our postretirement plan during 2021, 2020, and 2019: Pension Benefits Postretirement Benefits 2021 2020 2019 2021 2020 2019 Ameren Missouri $ 22 $ 17 $ 3 $ 1 $ 1 $ 1 Ameren Illinois 28 27 19 1 1 1 Ameren Services 10 8 1 — — 1 Ameren $ 60 $ 52 $ 23 $ 2 $ 2 $ 3
Target Allocation Of The Plans' Asset Categories	The following table presents our target allocations and our pension and postretirement plans’ asset categories as of December 31, 2021 and 2020: Asset Target Allocation 2021 (a) Percentage of Plan Assets at December 31, 2021 2020 Pension Plan: Cash and cash equivalents 0% – 5% 3 % 1 % Equity securities: U.S. large-capitalization 11% – 21% 23 % 26 % U.S. small- and mid-capitalization 3% – 13% 9 % 9 % International 9% – 19% 15 % 15 % Global 7% – 17% 11 % 9 % Total equity 45% – 55% 58 % 59 % Debt securities 35% – 45% 35 % 36 % Real estate 0% – 10% 4 % 4 % Private equity 0% – 5% (b) (b) Diversified credit 0% – 10% (b) (b) Total 100 % 100 % Postretirement Plans: Cash and cash equivalents 0% – 7% 3 % 3 % Equity securities: U.S. large-capitalization 23% – 33% 30 % 31 % U.S. small- and mid-capitalization 3% – 13% 9 % 8 % International 9% – 19% 13 % 15 % Global 5% – 15% 10 % 10 % Total equity 55% – 65% 62 % 64 % Debt securities 33% – 43% 35 % 33 % Total 100 % 100 % (a) These target allocations reflect targets that were approved in 2021 to take effect in the subsequent year. (b) Less than 1% of plan assets.
Components Of Net Periodic Benefit Cost	The following table presents the components of the net periodic benefit cost of Ameren’s pension and postretirement benefit plans during 2021, 2020, and 2019: Pension Benefits Postretirement Benefits 2021 2020 2019 2021 2020 2019 Service cost (a) $ 134 $ 110 $ 88 $ 23 $ 19 $ 18 Non-service cost components: Interest cost 152 174 187 33 39 43 Expected return on plan assets (297) (291) (276) (80) (80) (77) Amortization of: Prior service credit — (1) (1) (4) (4) (5) Actuarial (gain) loss 73 60 25 (6) (9) (15) Total non-service cost components (b) $ (72) $ (58) $ (65) $ (57) $ (54) $ (54) Net periodic benefit cost (income) $ 62 $ 52 $ 23 $ (34) $ (35) $ (36) (a) Service cost, net of capitalization, is reflected in “Operating Expenses - Other operations and maintenance” on Ameren’s statement of income. (b) Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 6 – Other Income, Net for additional information.
Summary Of Benefit Plan Costs Incurred	The Ameren Companies are responsible for their share of the pension and postretirement benefit costs. The following table presents the pension costs and the postretirement benefit costs incurred for the years ended December 31, 2021, 2020, and 2019: Pension Costs Postretirement Costs 2021 2020 2019 2021 2020 2019 Ameren Missouri (a) $ 29 $ 22 $ 5 $ (4) $ (5) $ (6) Ameren Illinois 34 32 20 (31) (31) (30) Other (1) (2) (2) 1 1 — Ameren $ 62 $ 52 $ 23 $ (34) $ (35) $ (36) (a) Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri and the level of such costs included in customer rates.
Schedule Of Expected Payments From Qualified Trust And Company Funds	The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2021, are as follows: Pension Benefits Postretirement Benefits Paid from Paid from Paid from Paid from 2022 $ 267 $ 2 $ 59 $ 2 2023 274 2 60 2 2024 279 3 61 2 2025 284 3 61 2 2026 288 3 60 2 2027 – 2031 1,476 12 296 9
Assumptions Used To Determine Net Periodic Benefit Cost	The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2021, 2020, and 2019: Pension Benefits Postretirement Benefits 2021 2020 2019 2021 2020 2019 Discount rate at measurement date 2.75 % 3.50 % 4.25 % 2.75 % 3.50 % 4.25 % Expected return on plan assets 6.50 7.00 7.00 6.50 7.00 7.00 Increase in future compensation 3.50 3.50 3.50 3.50 3.50 3.50 Cash balance pension plan interest crediting rate 5.00 5.00 5.00 (a) (a) (a) Medical cost trend rate (initial) (b) (a) (a) (a) 5.00 5.00 5.00 Medical cost trend rate (ultimate) (b) (a) (a) (a) 5.00 5.00 5.00 (a) Not applicable. (b) Initial and ultimate medical cost trend rate for certain Medicare-eligible participants is 3.00%.
Schedule Of Matching Contributions	The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to each of the Ameren Companies for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri $ 21 $ 20 $ 19 Ameren Illinois 16 17 16 Other 1 1 — Ameren $ 38 $ 38 $ 35
Pension Benefits
Target Allocation Of The Plans' Asset Categories	The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plans’ assets measured at fair value and NAV as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Level 1 Level 2 NAV Total Level 1 Level 2 NAV Total Cash and cash equivalents $ — $ — $ 116 $ 116 $ — $ — $ 145 $ 145 Equity securities: U.S. large-capitalization — — 1,381 1,381 — — 1,511 1,511 U.S. small- and mid-capitalization 558 — — 558 513 — — 513 International 372 — 531 903 375 — 492 867 Global — — 621 621 — — 546 546 Debt securities: Corporate bonds — 545 27 572 — 506 17 523 Municipal bonds — 50 — 50 — 50 — 50 U.S. Treasury and agency securities — 1,450 — 1,450 3 1,325 — 1,328 Other 17 11 — 28 (5) 8 — 3 Real estate — — 228 228 — — 208 208 Private equity — — 1 1 — — 2 2 Total $ 947 $ 2,056 $ 2,905 $ 5,908 $ 886 $ 1,889 $ 2,921 $ 5,696 Less: Medical benefit assets (a) (234) (219) Plus: Net receivables (b) 71 33 Fair value of pension plans’ assets $ 5,745 $ 5,510 (a) Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. (b) Receivables related to pending securities sales, offset by payables related to pending securities purchases.
Postretirement Benefits
Target Allocation Of The Plans' Asset Categories	The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans’ assets measured at fair value and NAV as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Level 1 Level 2 NAV Total Level 1 Level 2 NAV Total Cash and cash equivalents $ 24 $ — $ — $ 24 $ 38 $ — $ — $ 38 Equity securities: U.S. large-capitalization 283 — 115 398 279 — 107 386 U.S. small- and mid-capitalization 113 — — 113 104 — — 104 International 60 — 117 177 75 — 107 182 Global — — 132 132 — — 120 120 Debt securities: Municipal bonds — 133 — 133 — 106 — 106 Other — — 335 335 — — 295 295 Total $ 480 $ 133 $ 699 $ 1,312 $ 496 $ 106 $ 629 $ 1,231 Plus: Medical benefit assets (a) 234 219 Plus: Net receivables (b) 12 3 Fair value of postretirement benefit plans’ assets $ 1,558 $ 1,453 (a) Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above. (b) Receivables related to pending securities sales, offset by payables related to pending securities purchases.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary Of Nonvested Shares Related To Long-Term Incentive Plan	The following table summarizes Ameren’s nonvested performance share unit and restricted stock unit activity for the year ended December 31, 2021: Performance Share Units – Market Condition (a) Performance Share Units – Performance Condition (b) Restricted Stock Units Share Weighted-average Fair Value per Share Unit Shares Weighted-average Fair Value per Share Unit Stock Weighted-average Fair Value per Stock Unit Nonvested at January 1, 2021 (c) 464,139 $ 73.34 31,896 $ 76.66 303,695 $ 68.52 Granted 266,081 87.11 42,672 78.11 129,723 78.17 Forfeitures (21,143) 80.77 (2,449) 77.55 (10,209) 74.88 Vested and undistributed (d) (186,792) 77.91 (15,134) 77.27 (87,427) 73.13 Vested and distributed (93,499) 62.88 — — (87,597) 56.38 Performance share adjustment — — (13,881) 77.54 — — Nonvested at December 31, 2021 (e) 428,786 $ 81.81 43,104 $ 77.54 248,185 $ 75.97 (a) The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the specified market conditions. Compensation cost on nonforfeited awards is recognized regardless of whether Ameren achieves the specified market conditions. (b) The exact number of shares issued pursuant to a share unit varies from 0% to 200% of the target award, depending on actual company performance relative to the performance goals. Compensation cost is recognized ratably over the requisite service period only for awards for which it is probable that the performance condition will be satisfied. The performance share adjustment represents the change in the probability that a performance condition will be satisfied. (c) Does not include 366,243 market condition performance share units, 7,607 performance shares based on Ameren’s clean energy transition, and 160,034 restricted stock units that were vested and undistributed. (d) Vested and undistributed units are awards that vest on a pro-rata basis due to attainment of retirement eligibility by certain employees, but have not yet been distributed. For vested and undistributed performance share units, the number of shares issued for retirement-eligible employees will vary depending on actual performance over the three-year performance period. (e) Does not include 357,575 market condition performance share units, 22,739 performance shares based on Ameren’s clean energy transition, and 164,000 restricted stock units that were vested and undistributed.
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award	The following table presents the fair value of each share unit along with the significant assumptions used to calculate the fair value of each share unit for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Fair value of share units awarded $87.11 $82.49 $67.42 Three-year risk-free rate 0.17% 1.62% 2.46% Ameren’s common stock volatility (a) 28% 15% 17% Volatility range for the peer group (a) 26% – 36% 14% – 28% 15% – 25% (a) Based on a historical period that is equal to the remaining term of the performance period as of the grant date. The following table presents the stock-based compensation expense for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri $ 5 $ 5 $ 4 Ameren Illinois 3 3 3 Other (a) 14 13 13 Ameren 22 21 20 Less: Income tax benefit 6 6 5 Stock-based compensation expense, net $ 16 $ 15 $ 15 (a) Represents compensation expense for employees of Ameren Services. These amounts are not included in the Ameren Missouri and Ameren Illinois amounts above.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule Of Effective Income Tax Rate Reconciliation	The following table presents the principal reasons for the difference between the effective income tax rate and the federal statutory corporate income tax rate for the years ended December 31, 2021, 2020, and 2019: Ameren Missouri Ameren Illinois Ameren 2021 Federal statutory corporate income tax rate 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred income taxes (15) (3) (8) Amortization of deferred investment tax credit (1) — — Renewable and other tax credits (7) (a) — (3) (a) State tax 3 7 5 Stock-based compensation — — (1) Effective income tax rate 1 % 25 % 14 % 2020 Federal statutory corporate income tax rate 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred income taxes (16) (3) (9) Amortization of deferred investment tax credit (1) (1) (1) State tax 3 7 5 Stock-based compensation — — (1) Effective income tax rate 7 % 24 % 15 % 2019 Federal statutory corporate income tax rate 21 % 21 % 21 % Increases (decreases) from: Amortization of excess deferred income taxes (11) (4) (7) Amortization of deferred investment tax credit (1) — (1) State tax 5 7 6 Stock-based compensation — — (1) Effective income tax rate 14 % 24 % 18 %
Schedule Of Components Of Income Tax Expense (Benefit)	The following table presents the components of income tax expense (benefit) for the years ended December 31, 2021, 2020, and 2019: Ameren Missouri Ameren Illinois Other Ameren 2021 Current taxes: Federal $ — $ (15) $ 22 $ 7 State — (7) 1 (6) Deferred taxes: Federal 65 120 (15) 170 State 23 59 4 86 Amortization of excess deferred income taxes (81) (14) (1) (96) Amortization of deferred investment tax credits (4) — — (4) Total income tax expense $ 3 $ 143 $ 11 $ 157 2020 Current taxes: Federal $ 14 $ 12 $ (24) $ 2 State 3 (6) 8 5 Deferred taxes: Federal 82 81 24 187 State 15 52 (10) 57 Amortization of excess deferred income taxes (75) (15) (1) (91) Amortization of deferred investment tax credits (5) — — (5) Total income tax expense (benefit) $ 34 $ 124 $ (3) $ 155 2019 Current taxes: Federal $ 65 $ 19 $ (88) $ (4) State 22 11 (14) 19 Deferred taxes: Federal 37 66 82 185 State 5 29 25 59 Amortization of excess deferred income taxes (56) (15) (1) (72) Amortization of deferred investment tax credits (5) — — (5) Total income tax expense $ 68 $ 110 $ 4 $ 182
Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences	The following table presents the accumulated deferred income tax assets and liabilities recorded as a result of temporary differences and accumulated deferred investment tax credits at December 31, 2021 and 2020: Ameren Missouri Ameren Illinois Other Ameren 2021 Accumulated deferred income taxes, net liability (asset): Plant-related $ 2,188 $ 1,715 $ 226 $ 4,129 Regulatory assets and liabilities, net (259) (199) (25) (483) Deferred employee benefit costs (52) 17 (53) (88) Tax carryforwards (68) (46) (84) (198) Other 13 71 25 109 Total net accumulated deferred income tax liabilities (assets) 1,822 1,558 89 3,469 Accumulated deferred investment tax credits 30 — — 30 Accumulated deferred income taxes and investment tax credits $ 1,852 $ 1,558 $ 89 $ 3,499 2020 Accumulated deferred income taxes, net liability (asset): Plant-related $ 2,112 $ 1,559 $ 205 $ 3,876 Regulatory assets and liabilities, net (285) (207) (23) (515) Deferred employee benefit costs (58) 8 (54) (104) Tax carryforwards (26) (6) (65) (97) Other (35) 13 39 17 Total net accumulated deferred income tax liabilities (assets) 1,708 1,367 102 3,177 Accumulated deferred investment tax credits 34 — — 34 Accumulated deferred income taxes and investment tax credits $ 1,742 $ 1,367 $ 102 $ 3,211
Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards	The following table presents the components of accumulated deferred income tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2021 and 2020: Ameren Missouri Ameren Illinois Other Ameren 2021 Net operating loss carryforwards: Federal (a) $ 2 $ 17 $ 15 $ 34 State (b) $ 1 $ 25 $ 5 $ 31 Total net operating loss carryforwards $ 3 $ 42 $ 20 $ 65 Tax credit carryforwards: Federal (c) $ 65 $ 3 $ 58 $ 126 State (d) — 1 6 7 Total tax credit carryforwards $ 65 $ 4 $ 64 $ 133 2020 Net operating loss carryforwards: State $ — $ 3 $ 4 $ 7 Total net operating loss carryforwards $ — $ 3 $ 4 $ 7 Tax credit carryforwards: Federal $ 26 $ 3 $ 54 $ 83 State — — 7 7 Total tax credit carryforwards $ 26 $ 3 $ 61 $ 90 (a) Will not expire. (b) Will expire between 2032 and 2041. (c) Will expire between 2030 and 2041. (d) Will expire between 2022 and 2026.

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Dec. 31, 2021
Related Party Transactions [Abstract]
Schedule of Related Party Electric Power Supply Agreements	The following table presents the specified performance period, price, and amount of MWhs included in the agreements: IPA Procurement Event Performance Period MWh Average Price per MWh April 2017 March 2019 – May 2020 85,600 $ 34 April 2018 June 2019 – September 2020 110,000 32 April 2019 January 2020 – December 2021 288,000 35 September 2019 April 2020 – November 2021 170,800 29 September 2020 September 2021 – November 2022 204,800 31 April 2021 July 2022 – November 2022 33,600 34 September 2021 January 2022 – September 2023 136,000 37
Schedule of Affiliate Receivables and Payables	The following table presents the affiliate balances related to income taxes for Ameren Missouri and Ameren Illinois as of December 31, 2021 and December 31, 2020: 2021 2020 Ameren Missouri Ameren Illinois Ameren Missouri Ameren Illinois Income taxes payable to parent (a) $ — $ 8 $ — $ 6 Income taxes receivable from parent (b) 27 18 9 15 (a) Included in “Accounts payable – affiliates” on the balance sheet.
Schedule of Capital Contributions	The following table presents cash capital contributions received from Ameren (parent) by Ameren Missouri and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri (a) $ 207 $ 491 $ 124 Ameren Illinois (a) 262 464 15 (a) Includes capital contributions made as a result of the tax allocation agreement.
Schedule of Related Party Transactions	The following table presents the impact on Ameren Missouri and Ameren Illinois of related-party transactions for the years ended December 31, 2021, 2020, and 2019. It is based primarily on the agreements discussed above and the money pool arrangements discussed in Note 4 – Short-term Debt and Liquidity. Agreement Income Statement Line Item Ameren Ameren Ameren Missouri power supply agreements Operating Revenues 2021 $ 16 $ (a) with Ameren Illinois 2020 11 (a) 2019 3 (a) Ameren Missouri and Ameren Illinois Operating Revenues 2021 26 1 rent and facility services 2020 26 1 2019 27 2 Ameren Missouri and Ameren Illinois miscellaneous Operating Revenues 2021 (b) 5 support services and services provided to ATXI 2020 3 1 2019 1 2 Ameren Missouri software licensing Operating Revenues 2021 (a) (a) with Ameren Illinois 2020 (a) (a) 2019 (a) 19 Total Operating Revenues 2021 $ 42 $ 6 2020 40 2 2019 31 23 Ameren Illinois power supply Purchased Power 2021 $ (a) $ 16 agreements with Ameren Missouri 2020 (a) 11 2019 (a) 3 Ameren Missouri and Ameren Illinois Purchased Power 2021 4 1 transmission services from ATXI 2020 (a) 2 2019 (a) 2 Total Purchased Power 2021 $ 4 $ 17 2020 (a) 13 2019 (a) 5 Ameren Missouri and Ameren Illinois Other Operations and 2021 $ 1 $ 4 rent and facility services Maintenance 2020 (b) 4 2019 2 5 Ameren Services support services Other Operations and 2021 147 137 agreement Maintenance 2020 140 133 2019 135 127 Total Other Operations and 2021 $ 148 $ 141 Maintenance Expenses 2020 140 137 2019 137 132 Money pool borrowings (advances) (Interest Charges) 2021 $ (b) $ (b) Other Income, Net 2020 (b) (b) 2019 (b) (b) (a) Not applicable. (b) Amount less than $1 million.

Supplemental Information (Table

Supplemental Information (Tables)	12 Months Ended
	Dec. 31, 2021
Supplemental Information [Abstract]
Schedule of Cash and Cash Equivalents Including Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets and the statements of cash flows as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Cash and cash equivalents $ 8 $ — $ — $ 139 $ 136 $ — Restricted cash included in “Other current assets” 16 4 6 17 5 6 Restricted cash included in “Other assets” 127 — 127 141 — 141 Restricted cash included in “Nuclear decommissioning trust fund” 4 4 — 4 4 — Total cash, cash equivalents, and restricted cash $ 155 $ 8 $ 133 $ 301 $ 145 $ 147 The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheet and the statement of cash flows as of December 31, 2021 and 2020: (In millions) 2021 2020 Cash and cash equivalents $ — $ — Restricted cash included in “Other current assets” 4 4 Total cash, cash equivalents, and restricted cash $ 4 $ 4
Schedule of Accounts, Notes, Loans and Financing Receivable	The following table provides a reconciliation of the beginning and ending amount of the allowance for doubtful accounts for the years ended December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Missouri Ameren Illinois (a) Ameren Ameren Missouri Ameren Illinois (a) Ameren Beginning of period $ 16 $ 34 $ 50 $ 7 $ 10 $ 17 Bad debt expense 5 4 (b) 9 15 33 48 Net write-offs (8) (22) (30) (6) (9) (15) End of period $ 13 $ 16 $ 29 $ 16 $ 34 $ 50 (a) Ameren Illinois has rate-adjustment mechanisms that allow it to recover the difference between its actual net bad debt write-offs under GAAP, including those associated with receivables purchased from alternative retail electric suppliers, and the amount of net bad debt write-offs included in its base rates. (b) In 2021, Ameren Illinois’ bad debt expense was reduced as a result of incremental state funding received for customer bill assistance. The incremental state funding granted relief to low-income customers at risk of service disconnection resulting from the impacts of the COVID-19 pandemic.
Schedule of Inventories	The following table presents the components of inventories for each of the Ameren Companies at December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Fuel (a) $ 118 $ — $ 118 $ 115 $ — $ 115 Natural gas stored underground 9 90 99 5 52 57 Materials, supplies, and other 292 83 375 266 83 349 Total inventories $ 419 $ 173 $ 592 $ 386 $ 135 $ 521 (a) Consists of coal, oil, and propane.
Schedule of Asset Retirement Obligations	The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Ameren Ameren Ameren Ameren Ameren Ameren Beginning balance at January 1 $ 751 $ 5 (a) $ 756 (b) $ 687 $ 4 $ 691 Liabilities incurred 18 (c) — 18 (c) 36 (c) — 36 (c) Liabilities settled (36) (1) (37) (58) — (58) Accretion (d) 31 — 31 29 1 30 Change in estimates (4) (e) — (4) (e) 57 (f) — 57 (f) Ending balance at December 31 $ 760 (g) $ 4 (a) $ 764 (b)(g) $ 751 $ 5 (a) $ 756 (b) (a) Included in “Other deferred credits and liabilities” on the balance sheet. (b) Balance included $7 million and $60 million in “Other current liabilities” on the balance sheet as of December 31, 2021 and 2020, respectively. (c) Ameren Missouri recorded AROs related to the decommissioning of the Atchison Renewable and High Prairie Renewable energy centers in 2021 and 2020, respectively. (d) Accretion expense attributable to Ameren Missouri and Ameren Illinois was recorded as a decrease to regulatory liabilities and an increase to regulatory assets, respectively. (e) Ameren Missouri changed its fair value estimate primarily due to a decrease in the cost estimate for closure of certain CCR storage facilities, partially offset by an increase due to the planned accelerated retirement of the Rush Island Energy Center. (f) Ameren Missouri changed its fair value estimate primarily due to an update to the decommissioning of the Callaway Energy Center to reflect the cost study and funding analysis filed with the MoPSC in November 2020 and an increase in the cost estimate for closure of certain CCR storage facilities. (g) The balance as of December 31, 2021, included an ARO related to the decommissioning of the Callaway Enter Center of $574 million.
Schedule of Excise Taxes	The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Ameren Missouri $ 150 $ 139 $ 147 Ameren Illinois 125 115 117 Ameren $ 275 $ 254 $ 264
Schedule of Rates and Amounts For Allowance for Funds Used During Construction	The following table presents the average rate that was applied to eligible construction work in progress and the amounts of allowance for funds used during construction capitalized in 2021, 2020, and 2019: 2021 2020 2019 Average rate: Ameren Missouri 6 % 5 % 6 % Ameren Illinois 5 % 5 % 5 % Ameren: Allowance for equity funds used during construction $ 43 $ 32 $ 28 Allowance for borrowed funds used during construction 17 16 20 Total Ameren $ 60 $ 48 $ 48 Ameren Missouri: Allowance for equity funds used during construction $ 26 $ 19 $ 19 Allowance for borrowed funds used during construction 10 10 12 Total Ameren Missouri $ 36 $ 29 $ 31 Ameren Illinois: Allowance for equity funds used during construction $ 17 $ 13 $ 9 Allowance for borrowed funds used during construction 7 6 8 Total Ameren Illinois $ 24 $ 19 $ 17
Schedule of Earnings Per Share, Basic and Diluted	The following table reconciles the weighted-average number of common shares outstanding to the diluted weighted-average number of common shares outstanding for the years ended December 31, 2021, 2020, and 2019: 2021 2020 2019 Weighted-average Common Shares Outstanding – Basic 256.3 247.0 245.6 Assumed settlement of performance share units and restricted stock units 1.3 1.2 1.4 Dilutive effect of forward sale agreements — 0.5 0.1 Weighted-average Common Shares Outstanding – Diluted (a) 257.6 248.7 247.1 (a) There was an immaterial number of anti-dilutive securities excluded from the earnings per diluted share calculations for the year ended December 31, 2021. There were no potentially dilutive securities excluded from the earnings per diluted share calculations for the years ended December 31, 2020 and 2019.
Schedule of Cash Flow, Supplemental Disclosures	The following table provides noncash financing and investing activity excluded from the statements of cash flows for the years ended December 31, 2021, 2020, and 2019: December 31, 2021 December 31, 2020 December 31, 2019 Ameren Ameren Ameren Ameren Ameren Ameren Ameren Ameren Ameren Investing Accrued capital expenditures, including wind generation expenditures $ 508 $ 285 $ 215 $ 446 $ 229 $ 218 $ 333 $ 140 $ 163 Accrued nuclear fuel expenditures 16 16 — — — — 19 19 — Net realized and unrealized gain – nuclear decommissioning trust fund 163 163 — 116 116 — 143 143 — Exchange of bond investments for the extinguishment of senior unsecured notes (a) — — — — — — 17 — 17 Financing Issuance of common stock for stock-based compensation $ 33 $ — $ — $ 38 $ — $ — $ 54 $ — $ — Exchange of bond investments for the extinguishment of senior unsecured notes (a) — — — — — — (17) — (17) (a) In 2006, Ameren Illinois purchased all $17 million of the 1993 Series B-1 bonds due 2028 issued by the Illinois Finance Authority on behalf of Ameren Illinois pursuant to a mandatory tender. Ameren Illinois’ 1993 Series B-1 senior unsecured notes due 2028 were not extinguished and remained as “Long-term debt, net” on Ameren’s and Ameren Illinois’ balance sheets. In September 2019, Ameren Illinois exchanged its bond investments for the extinguishment of its senior unsecured notes.

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information, By Segment	The following tables present information about the reported revenue and specified items reflected in net income attributable to common shareholders and capital expenditures by segment at Ameren and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019. Ameren, Ameren Missouri, and Ameren Illinois management review segment capital expenditure information rather than any individual or total asset amount. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Other Intersegment Eliminations Ameren 2021 External revenues $ 3,311 $ 1,635 $ 957 $ 491 $ — $ — $ 6,394 Intersegment revenues 42 4 — 71 — (117) — Depreciation and amortization 632 309 90 111 4 — 1,146 Interest income 26 1 — — 3 (3) 27 Interest charges 137 74 42 83 (a) 50 (3) 383 Income taxes (benefit) 3 53 39 82 (20) — 157 Net income (loss) attributable to Ameren common shareholders 518 165 108 230 (31) — 990 Capital expenditures 2,015 (b) 579 278 616 4 (13) 3,479 (b) 2020 External revenues $ 3,069 $ 1,496 $ 760 $ 469 $ — $ — $ 5,794 Intersegment revenues 40 2 — 54 — (96) — Depreciation and amortization 604 288 81 98 4 — 1,075 Interest income 26 2 — 1 4 (4) 29 Interest charges 190 72 41 78 (a) 42 (4) 419 Income taxes (benefit) 34 42 36 78 (35) — 155 Net income (loss) attributable to Ameren common shareholders 436 143 99 216 (23) — 871 Capital expenditures 1,666 (b) 543 301 716 5 2 3,233 (b) 2019 External revenues $ 3,212 $ 1,487 $ 791 $ 401 $ — $ — $ 5,891 Intersegment revenues 31 17 6 63 — (98) 19 (c) Depreciation and amortization 556 273 78 84 4 — 995 Interest income 26 6 — 1 5 (5) 33 Interest charges 178 71 38 74 (a) 25 (5) 381 Income taxes (benefit) 68 45 30 64 (25) — 182 Net income (loss) attributable to Ameren common shareholders 426 146 84 185 (13) — 828 Capital expenditures 1,076 518 318 528 3 (32) (d) 2,411 (a) Ameren Transmission interest charges include an allocation of financing costs from Ameren (parent). (b) Includes $525 million and $564 million at Ameren and Ameren Missouri for wind generation expenditures for the year ended December 31, 2021 and 2020, respectively. (c) Intersegment revenues at Ameren include $14 million and $5 million of revenue from Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively, for the year ended December 31, 2019, for a software licensing agreement with Ameren Missouri. Under authoritative accounting guidance for rate-regulated entities, the revenue recognized by Ameren Illinois was not eliminated upon consolidation. See Note 13 – Related-party Transactions for additional information. (d) Intersegment capital expenditure eliminations include $24 million of eliminations for the year ended December 31, 2019, for a software licensing agreement between Ameren Illinois and Ameren Missouri. See Note 13 – Related-party Transactions for additional information. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois 2021 External revenues $ 1,639 $ 957 $ 299 $ — $ 2,895 Intersegment revenues — — 66 (66) — Depreciation and amortization 309 90 73 — 472 Interest income 1 — — — 1 Interest charges 74 42 48 — 164 Income taxes 53 39 51 — 143 Net income available to common shareholder 165 108 152 — 425 Capital expenditures 579 278 575 — 1,432 2020 External revenues $ 1,498 $ 760 $ 277 $ — $ 2,535 Intersegment revenues — — 52 (52) — Depreciation and amortization 288 81 65 — 434 Interest income 2 — 1 — 3 Interest charges 72 41 42 — 155 Income taxes 42 36 46 — 124 Net income available to common shareholder 143 99 137 — 379 Capital expenditures 543 301 603 — 1,447 2019 External revenues $ 1,504 $ 797 $ 226 $ — $ 2,527 Intersegment revenues — — 62 (62) — Depreciation and amortization 273 78 55 — 406 Interest income 6 — — — 6 Interest charges 71 38 38 — 147 Income taxes 45 30 35 — 110 Net income available to common shareholder 146 84 113 — 343 Capital expenditures 518 318 372 — 1,208
Disaggregation of Revenue	The following tables present disaggregated revenues by segment at Ameren and Ameren Illinois for the years ended December 31, 2021, 2020, and 2019. Economic factors affect the nature, timing, amount, and uncertainty of revenues and cash flows in a similar manner across customer classes. Revenues from alternative revenue programs have a similar distribution among customer classes as revenues from contracts with customers. Other revenues not associated with contracts with customers are presented in the Other customer classification, along with electric transmission and off-system revenues. Ameren Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Intersegment Eliminations Ameren 2021 Residential $ 1,445 $ 933 $ — $ — $ — $ 2,378 Commercial 1,126 545 — — — 1,671 Industrial 280 135 — — — 415 Other 361 26 — 562 (116) 833 Total electric revenues $ 3,212 $ 1,639 $ — $ 562 $ (116) $ 5,297 Residential $ 79 $ — $ 657 $ — $ — $ 736 Commercial 34 — 172 — — 206 Industrial 4 — 35 — — 39 Other 24 — 93 — (1) 116 Total gas revenues $ 141 $ — $ 957 $ — $ (1) $ 1,097 Total revenues (a) $ 3,353 $ 1,639 $ 957 $ 562 $ (117) $ 6,394 2020 Residential $ 1,373 $ 867 $ — $ — $ — $ 2,240 Commercial 1,025 486 — — — 1,511 Industrial 261 124 — — — 385 Other 325 21 — 523 (94) 775 Total electric revenues $ 2,984 $ 1,498 $ — $ 523 $ (94) $ 4,911 Residential $ 76 $ — $ 541 $ — $ — $ 617 Commercial 29 — 136 — — 165 Industrial 4 — 14 — — 18 Other 16 — 69 — (2) 83 Total gas revenues $ 125 $ — $ 760 $ — $ (2) $ 883 Total revenues (a) $ 3,109 $ 1,498 $ 760 $ 523 $ (96) $ 5,794 2019 Residential $ 1,403 $ 848 $ — $ — $ — $ 2,251 Commercial 1,157 497 — — — 1,654 Industrial 278 127 — — — 405 Other 271 32 (b) — 464 (96) 671 Total electric revenues $ 3,109 $ 1,504 $ — $ 464 $ (96) $ 4,981 Residential $ 81 $ — $ 570 $ — $ — $ 651 Commercial 34 — 154 — — 188 Industrial 4 — 13 — — 17 Other 15 — 60 (b) — (2) 73 Total gas revenues $ 134 $ — $ 797 $ — $ (2) $ 929 Total revenues (a) $ 3,243 $ 1,504 $ 797 $ 464 $ (98) $ 5,910 (a) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the years ended December 31, 2021, 2020, and 2019: Ameren Missouri Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Transmission Ameren 2021 Revenues from alternative revenue programs $ (16) $ 77 $ 5 $ 11 $ 77 Other revenues not from contracts with customers 56 (a) 10 2 — 68 (a) 2020 Revenues from alternative revenue programs $ (14) $ (20) $ 20 $ 50 $ 36 Other revenues not from contracts with customers 25 8 2 1 36 2019 Revenues from alternative revenue programs $ 35 $ (74) $ — $ (31) $ (70) Other revenues not from contracts with customers 19 7 2 — 28 (a) Includes insurance recoveries related to lost sales associated with the Callaway Energy Center maintenance outage. See Note 9 – Callaway Energy Center for additional information. (b) Includes $14 million and $5 million for Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively, for the year ended December 31, 2019, for a software licensing agreement with Ameren Missouri. See Note 13 – Related-party Transactions for additional information. Ameren Illinois Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Intersegment Eliminations Ameren Illinois 2021 Residential $ 933 $ 657 $ — $ — $ 1,590 Commercial 545 172 — — 717 Industrial 135 35 — — 170 Other 26 93 365 (66) 418 Total revenues (a) $ 1,639 $ 957 $ 365 $ (66) $ 2,895 2020 Residential $ 867 $ 541 $ — $ — $ 1,408 Commercial 486 136 — — 622 Industrial 124 14 — — 138 Other 21 69 329 (52) 367 Total revenues (a) $ 1,498 $ 760 $ 329 $ (52) $ 2,535 2019 Residential $ 848 $ 570 $ — $ — $ 1,418 Commercial 497 154 — — 651 Industrial 127 13 — — 140 Other 32 (b) 60 (b) 288 (62) 318 Total revenues (a) $ 1,504 $ 797 $ 288 $ (62) $ 2,527 (a) The following table presents increases/(decreases) in revenues from alternative revenue programs and other revenues not from contracts with customers for the Ameren Illinois segments for the years ended December 31, 2021, 2020, and 2019: Ameren Illinois Electric Distribution Ameren Illinois Natural Gas Ameren Illinois Transmission Ameren Illinois 2021 Revenues from alternative revenue programs $ 77 $ 5 $ 9 $ 91 Other revenues not from contracts with customers 10 2 — 12 2020 Revenues from alternative revenue programs $ (20) $ 20 $ 42 $ 42 Other revenues not from contracts with customers 8 2 — 10 2019 Revenues from alternative revenue programs $ (74) $ — $ (33) $ (107) Other revenues not from contracts with customers 7 2 — 9 (b) Includes $14 million and $5 million for Ameren Illinois Electric Distribution and Ameren Illinois Natural Gas, respectively, for the year ended December 31, 2019, for a software licensing agreement with Ameren Missouri. See Note 13 – Related-party Transactions for additional information.

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) customer in Millions	12 Months Ended
	Dec. 31, 2021USD ($)mi²segmentcustomer	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Accounting Policies [Line Items]
Goodwill	$ 411,000,000	$ 411,000,000
Number of reportable segments | segment	4
Goodwill, Impairment Loss	$ 0
Noncontrolling Interest in Variable Interest Entity	56,000,000	37,000,000
Cash Surrender Value of Life Insurance	278,000,000	272,000,000
Loans, Gross, Insurance Policy	109,000,000	107,000,000
MISO Resettlements	$ 0
Union Electric Company
Accounting Policies [Line Items]
Public Utilities, Area Serviced | mi²	24,000
Number of Months Between Callaway Maintenance Outages	18 months
Ameren Illinois Company
Accounting Policies [Line Items]
Public Utilities, Area Serviced | mi²	43,700
Goodwill	$ 411,000,000	411,000,000
Number of reportable segments | segment	3
Goodwill, Impairment Loss	$ 0
Cash Surrender Value of Life Insurance	$ 117,000,000	$ 115,000,000
Minimum
Accounting Policies [Line Items]
Percent of average depreciable cost	3.00%	3.00%	3.00%
Maximum
Accounting Policies [Line Items]
Percent of average depreciable cost	4.00%	4.00%	4.00%
Electric | Union Electric Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers | customer	1.2
Power | Ameren Illinois Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers | customer	1.2
Natural gas | Union Electric Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers | customer	0.1
Natural gas | Ameren Illinois Company
Accounting Policies [Line Items]
Public Utilities, Number of Customers | customer	0.8
Ameren Illinois Electric Distribution
Accounting Policies [Line Items]
Goodwill	$ 238,000,000
Ameren Illinois Gas
Accounting Policies [Line Items]
Goodwill	80,000,000
Ameren Illinois Transmission
Accounting Policies [Line Items]
Goodwill	93,000,000
Ameren Transmission
Accounting Policies [Line Items]
Goodwill	93,000,000
AROs | Union Electric Company
Accounting Policies [Line Items]
Noncash Depreciation related to ARO	14,000,000	$ 28,000,000	$ 18,000,000
Partnership Funding Commitment [Member]
Accounting Policies [Line Items]
Unrecorded Unconditional Purchase Obligation	$ 28,000,000

Rate and Regulatory Matters (Re

Rate and Regulatory Matters (Regulatory Framework-Missouri) (Details) - Union Electric Company	12 Months Ended
	Dec. 31, 2021MWh
Public Utilities, General Disclosures [Line Items]
Number of months to complete a regulatory rate review	11 months
PISA Deferral Percentage	85.00%
Depreciation Percentage Not Included in PISA Deferral	15.00%
Sharing Level For Fac	95.00%
Percentage of variance not covered by FAC	5.00%
Amount of Megawatts	102
Frequency Rates Must be Reset to Use the FAC	4 years
Maximum
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage	2.85%
PISA
Public Utilities, General Disclosures [Line Items]
Amortization Period	20 years

Rate and Regulatory Matters (_2

Rate and Regulatory Matters (Regulatory Framework-Illinois) (Details) - Ameren Illinois Company	12 Months Ended
	Dec. 31, 2021
FEJA
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	5.80%
Return on equity adjustment	2.00%
QIP rider
Public Utilities, General Disclosures [Line Items]
QIP recovery begin date	2 months
QIP rider reset	zero
Natural gas
Public Utilities, General Disclosures [Line Items]
Number of months to complete a regulatory rate review	11 months
Electric Distribution | FEJA
Public Utilities, General Disclosures [Line Items]
Amortization Period	2 years
Return on equity penalty	0.10%
Maximum | QIP rider
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Percentage	4.00%
Annual QIP rate cap	5.50%
Maximum | Electric Distribution | FEJA
Public Utilities, General Disclosures [Line Items]
Return on equity penalty	0.38%

Rate and Regulatory Matters (_3

Rate and Regulatory Matters (Regulatory Framework-Federal) (Details)	12 Months Ended
	Dec. 31, 2021
Midwest Independent Transmission System Operator, Inc
Public Utilities, General Disclosures [Line Items]
Incentive adder to FERC allowed base return on common equity	0.50%
FERC revenue requirement reconciliation adjustment
Public Utilities, General Disclosures [Line Items]
Amortization Period	2 years

Rate and Regulatory Matters (Na

Rate and Regulatory Matters (Narrative-Missouri) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Feb. 28, 2021
Public Utilities, General Disclosures [Line Items]
Depreciation and amortization	$ 1,146	$ 1,075	$ 995
Other operations and maintenance	1,774	1,661	1,745
Regulatory assets	1,289	1,100
Revenues	6,394	5,794	5,910
Union Electric Company
Public Utilities, General Disclosures [Line Items]
Depreciation and amortization	632	604	556
Other operations and maintenance	$ 948	886	960
Sharing Level For Fac	95.00%
Percentage of variance not covered by FAC	5.00%
Regulatory assets	$ 523	347
Final Rate Order | Union Electric Company
Public Utilities, General Disclosures [Line Items]
COVID-19 pandemic costs	9
Regulatory assets	5
Revenues	4
Final Rate Order | Union Electric Company | Electric
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	220
Rate Base	$ 10,200
Public Utilities, Approved Equity Capital Structure, Percentage	51.97%
Depreciation and amortization	$ 140
Other operations and maintenance	40
Meramec Energy Center costs	61
Final Rate Order | Union Electric Company | Natural gas
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	5
Rate Base	313
Final Rate Order | Union Electric Company | MEEIA 2019 [Domain] | Electric
Public Utilities, General Disclosures [Line Items]
Revenues	9	$ 6
Incentive award if energy efficiency goals are achieved	13
MEEIA Energy Efficiency Investments For The 2023 Program Year	$ 75
Final Rate Order | Union Electric Company | MEEIA 2013 & 2016 | Electric
Public Utilities, General Disclosures [Line Items]
Revenues			$ 37
Under Recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets				$ 53
Minimum | Under Recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amortization Period	12 months
Maximum | Under Recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amortization Period	36 months

Rate And Regulatory Matters (_4

Rate And Regulatory Matters (Narrative-Illinois) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)windGenerationFacility	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 2,954	$ 2,669	$ 2,411
Revenues	6,394	5,794	5,910
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Capital expenditures	1,432	1,447	1,208
Revenues	2,895	$ 2,535	$ 2,527
Annual investment in energy-efficiency programs	$ 100
Deferred payment arrangement extension	18 months
Financial assistance program costs	$ 4
IETL | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Energy Transition Assistance Fund Surcharge	25
Annual investment in energy-efficiency programs	$ 120
IETL | Electric Distribution | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Rate Case Filing Frequency	4 years
Public Utilities, Approved Equity Capital Structure, Percentage	50.00%
Multi-Year Rate Plan Reconciliation Cap	105.00%
Amortization Period	2 years
Amortization Start Date	1 year
IETL | Electric Distribution | Ameren Illinois Company | Minimum
Public Utilities, General Disclosures [Line Items]
Return on Equity Adjustment	0.20%
Public Utilities, Requested Rate Increase (Decrease), Percentage	50.00%
IETL | Electric Distribution | Ameren Illinois Company | Maximum
Public Utilities, General Disclosures [Line Items]
Return on Equity Adjustment	0.60%
IETL | Electricity, Generation | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Capital expenditures	$ 20
Number of Solar Generation Pilot Projects | windGenerationFacility	2
Renewable energy credits and zero emission credits | Electricity, Generation | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Revenues	$ 100
IEIMA revenue requirement reconciliation adjustment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Amortization Period	2 years
Public Utilities, Approved Return on Equity, Percentage	5.80%
Final Rate Order | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Electric Energy-Efficiency Revenue Requirement	$ 61
Pending Rate Case | Natural gas | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Natural Gas Capital Investment Prudency Challenge	70
Challenged Recoveries Under the QIP	$ 3
IEIMA revenue requirement reconciliation adjustment | Final Rate Order | Electric Distribution | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Equity Capital Structure, Percentage	51.00%
Amortization Period	2 years
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 58
FEJA energy-efficiency rider | Final Rate Order | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 10

Rate and Regulatory Matters (_5

Rate and Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	May 31, 2020	Nov. 30, 2019	Dec. 31, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities			$ 5,848	$ 5,282
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities			$ 2,374	$ 2,063
Midwest Independent Transmission System Operator, Inc
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage			12.38%
Incentive adder to FERC allowed base return on common equity			0.50%
Final Rate Order | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities			$ 9
Final Rate Order | Midwest Independent Transmission System Operator, Inc
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	10.02%	9.88%	10.32%
Customer Requested Rate on Equity			9.15%
Incentive adder to FERC allowed base return on common equity			0.50%
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Maximum
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage			10.82%

Rate And Regulatory Matters (Sc

Rate And Regulatory Matters (Schedule Of Regulatory Assets And Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Feb. 28, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 1,608		$ 1,209
Current regulatory assets	(319)		(109)
Regulatory Assets, Noncurrent	1,289		1,100
Regulatory Liabilities	5,961		5,403
Current regulatory liabilities	(113)		(121)
Regulatory Liability, Noncurrent	5,848		5,282
Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	650		407
Current regulatory assets	(127)		(60)
Regulatory Assets, Noncurrent	523		347
Regulatory Liabilities	3,411		3,136
Current regulatory liabilities	(57)		(26)
Regulatory Liability, Noncurrent	$ 3,354		3,110
PISA Deferral Percentage	85.00%
Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 932		779
Current regulatory assets	(180)		(37)
Regulatory Assets, Noncurrent	752		742
Regulatory Liabilities	2,428		2,151
Current regulatory liabilities	(54)		(88)
Regulatory Liability, Noncurrent	2,374		2,063
Under-recovered FAC
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	47		48
Under-recovered FAC | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	47		48
Under-recovered FAC | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Under Recovered PGA
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	163		2
Under Recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	49	$ 53	0
Regulatory Assets, Noncurrent		53
Under Recovered PGA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 114	$ 221	2
Regulatory Asset, Amortization Period	18 months
MTM derivative losses
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 202		221
MTM derivative losses | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	77		21
MTM derivative losses | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	125		200
IEIMA revenue requirement reconciliation adjustment
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	42		0
Regulatory Liabilities	0		22
IEIMA revenue requirement reconciliation adjustment | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Regulatory Liabilities	0		0
IEIMA revenue requirement reconciliation adjustment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	42		0
Regulatory Liabilities	$ 0		22
Amortization Period	2 years
FERC revenue requirement reconciliation adjustment
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 43		50
Regulatory Liabilities	$ 4		21
Amortization Period	2 years
FERC revenue requirement reconciliation adjustment | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0		0
Regulatory Liabilities	0		0
FERC revenue requirement reconciliation adjustment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	18		28
Regulatory Liabilities	2		21
Under/Over-recovered VBA
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	17		11
Under/Over-recovered VBA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Under/Over-recovered VBA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	17		11
Income taxes
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	185		183
Regulatory Liabilities	$ 2,066		2,192
Weighted-Average Amortization Period	35 years
Income taxes | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 115		117
Regulatory Liabilities	$ 1,208		1,317
Weighted-Average Amortization Period	28 years
Income taxes | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 69		65
Regulatory Liabilities	$ 770		790
Weighted-Average Amortization Period	42 years
Bad debt rider
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 8		11
Regulatory Liabilities	19		5
Bad debt rider | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Regulatory Liabilities	0		0
Bad debt rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	8		11
Regulatory Liabilities	19		5
Callaway refueling and maintenance outage costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	14		39
Callaway refueling and maintenance outage costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 14		39
Regulatory Asset, Amortization Period	18 months
Callaway refueling and maintenance outage costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0		0
Unamortized loss on reacquired debt
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	63		74
Unamortized loss on reacquired debt | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	50		52
Unamortized loss on reacquired debt | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	13		22
Environmental cost riders
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	70		93
Environmental cost riders | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Environmental cost riders | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	70		93
Storm costs
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	17		7
Storm costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Storm costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	17		7
Allowance for funds used during construction for pollution control equipment
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	13		15
Allowance for funds used during construction for pollution control equipment | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	13		15
Allowance for funds used during construction for pollution control equipment | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Customer generation rebate program
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	47		17
Customer generation rebate program | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
Customer generation rebate program | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	47		17
PISA
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	244		78
PISA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 244		78
Amortization Period	20 years
Regulatory Asset, Amortization Period	20 years
PISA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	$ 0		0
FEJA energy-efficiency rider
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	350		283
FEJA energy-efficiency rider | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	0		0
FEJA energy-efficiency rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	350		283
Other regulatory assets
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	83		77
Other regulatory assets | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	41		37
Other regulatory assets | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Assets	42		40
Over-recovered FAC
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	19		10
Over-recovered FAC | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 19		10
Accumulation Period	4 months
Amortization Period	8 months
Over-recovered FAC | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 0		0
Over-recovered Illinois electric power costs
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	13		15
Over-recovered Illinois electric power costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0		0
Over-recovered Illinois electric power costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 13		15
Amortization Period	1 year
Over-recovered PGA
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 1		22
Over-recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0		7
Over-recovered PGA | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	1		15
MTM derivative gains
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	91		21
MTM derivative gains | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	50		11
MTM derivative gains | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	41		10
Cost of removal
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	1,988		1,923
Cost of removal | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	1,028		1,027
Cost of removal | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	929		873
AROs
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	603		436
AROs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	603		436
AROs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0		0
Pension and postretirement benefit costs
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	791		375
Pension and postretirement benefit costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	399		198
Pension and postretirement benefit costs | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	392		177
Pension and postretirement benefit costs tracker
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	28		55
Pension and postretirement benefit costs tracker | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 28		55
Regulatory Liability, Amortization Period	5 years
Pension and postretirement benefit costs tracker | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 0		0
Renewable energy credits and zero emission credits
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	246		200
Renewable energy credits and zero emission credits | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0		0
Renewable energy credits and zero emission credits | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	246		200
RESRAM
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	19		2
RESRAM | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	19		2
RESRAM | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0		0
Excess income taxes collected in 2018
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	25		45
Excess income taxes collected in 2018 | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	25		45
Excess income taxes collected in 2018 | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	0		0
Other regulatory liabilities
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	48		59
Other regulatory liabilities | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	32		28
Other regulatory liabilities | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 15		23
FAC adjustments | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Accumulation Period	4 months
Asset Retirement Obligation - Nuclear decommissioning trust fund balance | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 1,159		982
Asset Retirement Obligation - removal costs | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Regulatory Liabilities	$ 556		$ 546
Minimum | Under Recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amortization Period	12 months
Regulatory Asset, Amortization Period	12 months
Minimum | FEJA energy-efficiency rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Amortization Period	5 years
Maximum | Under Recovered PGA | Union Electric Company
Public Utilities, General Disclosures [Line Items]
Amortization Period	36 months
Regulatory Asset, Amortization Period	36 months
Maximum | FEJA energy-efficiency rider | Ameren Illinois Company
Public Utilities, General Disclosures [Line Items]
Regulatory Asset, Amortization Period	13 years

Property And Plant, Net (Schedu

Property And Plant, Net (Schedule Of Property And Plant, Net) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)equipment	Dec. 31, 2020USD ($)
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	$ 41,602	$ 39,719
Accumulated depreciation and amortization	14,214	13,773
Property and plant, before construction work in progress	27,388	25,946
Property, Plant and Equipment, Net	$ 29,261	26,807
Number of combustion turbine electric generation equipment with related financing obligations | equipment	2
Number of financing obligations | equipment	2
Gross asset value, financing obligations	$ 243	240
Total accumulated depreciation, financing obligations	105	99
Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,955	4,875
Plant To Be Abandoned, Net	604
Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,105	1,097
Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,615	5,608
Renewable Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,889	1,301
Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	14,303	13,433
Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	7,533	6,831
Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	4,193	3,869
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,009	2,705
Construction work in progress	1,136	786
Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	133	75
Oil Fired Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	29	36
Union Electric Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	23,669	23,098
Accumulated depreciation and amortization	9,784	9,689
Property and plant, before construction work in progress	13,885	13,409
Property, Plant and Equipment, Net	15,296	13,879
Union Electric Company | Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,955	4,875
Plant To Be Abandoned, Net	604
Union Electric Company | Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,105	1,097
Union Electric Company | Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	5,615	5,608
Union Electric Company | Renewable Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,889	1,301
Union Electric Company | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	7,286	6,784
Union Electric Company | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,628	1,482
Union Electric Company | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	607	561
Union Electric Company | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,584	1,390
Construction work in progress	674	395
Union Electric Company | Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	133	75
Ameren Illinois Company
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	15,891	14,602
Accumulated depreciation and amortization	4,100	3,780
Property and plant, before construction work in progress	11,791	10,822
Property, Plant and Equipment, Net	12,223	11,201
Ameren Illinois Company | Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Plant To Be Abandoned, Net	0
Ameren Illinois Company | Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Renewable Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Ameren Illinois Company | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	7,017	6,649
Ameren Illinois Company | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	4,105	3,575
Ameren Illinois Company | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	3,586	3,308
Ameren Illinois Company | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,183	1,070
Construction work in progress	432	379
Ameren Illinois Company | Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	0	0
Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	2,042	2,019
Accumulated depreciation and amortization	330	304
Property and plant, before construction work in progress	1,712	1,715
Property, Plant and Equipment, Net	1,742	1,727
Other | Coal Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Plant To Be Abandoned, Net	0
Other | Natural Gas and Oil Fired Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Nuclear Powered Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Renewable Electric Generation Equipment
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Electric distribution
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Electric transmission
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	1,800	1,774
Other | Natural gas
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	0	0
Other | Other
Property, Plant and Equipment [Line Items]
Property and plant, at original cost	242	245
Construction work in progress	30	12
Other | Nuclear fuel in process
Property, Plant and Equipment [Line Items]
Construction work in progress	$ 0	$ 0
Minimum | Electric distribution
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum | Electric transmission
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Minimum | Natural gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	20 years
Minimum | Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Minimum | Electric generation
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Maximum | Electric distribution
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	80 years
Maximum | Electric transmission
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	75 years
Maximum | Natural gas
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	80 years
Maximum | Other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	55 years
Maximum | Electric generation
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	72 years
Maximum | Union Electric Company | Electric generation
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	150 years

Property and Plant, Net (Sche_2

Property and Plant, Net (Schedule of Capitalized Software) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Capitalized software costs
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 125	$ 93	$ 78
Gross carrying value	1,199	1,021
Accumulated amortization	(757)	(640)
Union Electric Company | Capitalized software costs
Finite-Lived Intangible Assets [Line Items]
Amortization expense	66	44	30
Gross carrying value	523	398
Accumulated amortization	(255)	(189)
Ameren Illinois Company | Capitalized software costs
Finite-Lived Intangible Assets [Line Items]
Amortization expense	53	45	$ 45
Gross carrying value	452	397
Accumulated amortization	$ (291)	$ (238)
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	15 years

Property and Plant, Net (Sche_3

Property and Plant, Net (Schedule of Capitalized Software, Future Amortization Expense) (Details) - Capitalized software costs $ in Millions	Dec. 31, 2021USD ($)
Finite-Lived Intangible Assets [Line Items]
2022	$ 135
2023	119
2024	87
2025	47
2026	21
Union Electric Company
Finite-Lived Intangible Assets [Line Items]
2022	75
2023	69
2024	54
2025	31
2026	14
Ameren Illinois Company
Finite-Lived Intangible Assets [Line Items]
2022	56
2023	47
2024	31
2025	14
2026	$ 6

Short-Term Debt And Liquidity_2

Short-Term Debt And Liquidity (Narrative) (Details)	12 Months Ended
	Dec. 31, 2021USD ($)lender	Dec. 31, 2020
Multiyear Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 2,300,000,000
Line of Credit Facility, Commitment Fee Amount	$ 100,000,000
Actual debt-to-capital ratio	0.58
Multiyear Credit Facility | Maximum
Short-term Debt [Line Items]
Actual debt-to-capital ratio	0.65
Missouri Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,200,000,000
Illinois Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,100,000,000
Credit Agreements
Short-term Debt [Line Items]
Net Liquidity Available	1,800,000,000
Covenant terms, default provisions, maximum indebtedness	100,000,000
Parent Company | Missouri Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900,000,000
Parent Company | Illinois Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	500,000,000
Union Electric Company | Missouri Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 850,000,000
Actual debt-to-capital ratio	0.49
Ameren Illinois Company | Illinois Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 800,000,000
Actual debt-to-capital ratio	0.45
Utilities [Member]
Short-term Debt [Line Items]
Short Term Debt, Weighted Average Interest Rate During Period	0.17%	0.64%
Multiyear Credit Facility
Short-term Debt [Line Items]
Number of lenders | lender	22
Line of credit facility, maximum borrowing capacity, per lender	$ 130,000,000
Multiyear Credit Facility | Missouri Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	1,400,000,000
Multiyear Credit Facility | Illinois Credit Agreement 2012
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,300,000,000

Short-Term Debt And Liquidity_3

Short-Term Debt And Liquidity (Schedule Of Maximum Aggregate Amount Available On Credit Agreements) (Details) $ in Millions	Dec. 31, 2021USD ($)
Missouri Credit Agreement 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,200
Missouri Credit Agreement 2012 | Parent Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	900
Missouri Credit Agreement 2012 | Union Electric Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	850
Illinois Credit Agreement 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,100
Illinois Credit Agreement 2012 | Parent Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	500
Illinois Credit Agreement 2012 | Ameren Illinois Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 800

Short-Term Debt And Liquidity_4

Short-Term Debt And Liquidity (Commercial Paper) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Average daily amount outstanding	$ 604	$ 263
Commercial paper issuances outstanding at period-end	$ 545	$ 490
Weighted-average interest rate	0.22%	1.31%
Peak amount outstanding during period(a)	$ 1,134	$ 908
Peak interest rate	0.38%	5.05%
Parent Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 387	$ 108
Commercial paper issuances outstanding at period-end	$ 277	$ 490
Weighted-average interest rate	0.22%	1.04%
Peak amount outstanding during period(a)	$ 650	$ 490
Peak interest rate	0.38%	3.30%
Union Electric Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 99	$ 109
Commercial paper issuances outstanding at period-end	$ 165	$ 0
Weighted-average interest rate	0.22%	1.73%
Peak amount outstanding during period(a)	$ 546	$ 573
Peak interest rate	0.35%	5.05%
Ameren Illinois Company
Short-term Debt [Line Items]
Average daily amount outstanding	$ 118	$ 46
Commercial paper issuances outstanding at period-end	$ 103	$ 0
Weighted-average interest rate	0.21%	0.97%
Peak amount outstanding during period(a)	$ 485	$ 250
Peak interest rate	0.35%	3.40%

Long-Term Debt And Equity Fin_3

Long-Term Debt And Equity Financings (Narrative) (Details)	Dec. 31, 2021USD ($)windGenerationFacility$ / sharesshares	Jan. 31, 2022$ / shares	Oct. 31, 2020USD ($)	Dec. 31, 2022USD ($)	Dec. 31, 2021USD ($)windGenerationFacility$ / sharesshares	Dec. 31, 2021USD ($)windGenerationFacility$ / sharesshares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares	Jan. 03, 2022shares	Dec. 30, 2021shares	Sep. 03, 2021shares	May 31, 2021USD ($)	Feb. 11, 2021USD ($)	Dec. 29, 2020USD ($)	Oct. 30, 2020USD ($)	Feb. 03, 2020USD ($)	Aug. 05, 2019shares
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized (in shares) | shares	100,000,000				100,000,000	100,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.01				$ 0.01	$ 0.01
Preferred stock, shares outstanding (in shares) | shares	0				0	0
Shares issued under the DRPlus and 401(k) plan | shares						500,000	700,000	900,000
Issuances of common stock						$ 308,000,000	$ 476,000,000	$ 68,000,000
Stock Issued During Period, Shares, Other | shares						500,000	500,000	800,000
Stock Issued						$ 33,000,000	$ 38,000,000	$ 54,000,000
Common Stock, Shares Authorized Under DRPlus Plan | shares	4,000,000				4,000,000	4,000,000
Common Stock, Shares Authorized Under 401(k) Plan | shares	4,000,000				4,000,000	4,000,000
Maximum Value Of Shares To Be Issued Under ATM Program												$ 750,000,000
Quantity Of Shares Issued Under ATM Program | shares						1,800,000
Value of shares issued under ATM program						$ 148,000,000
Payments of Stock Issuance Costs						$ 2,000,000
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares																	7,500,000
Initial forward sale price, basis spread	75				75	75
Shares issued under forward sale agreement | shares						1,600,000	5,900,000	0
Common Stock Value Issued Through Forward Sale Agreement													$ 113,000,000	$ 425,000,000
Year One	$ 505,000,000				$ 505,000,000	$ 505,000,000
Debt Default Provision Excess						$ 25,000,000
September 2021 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares											400,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares					$ 87.87
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares	400,000				400,000	400,000
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 30,000,000				$ 30,000,000	$ 30,000,000
December 2021 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares										500,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares	$ 87.03
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value | shares	500,000				500,000	500,000
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	$ 41,000,000				$ 41,000,000	$ 41,000,000
Dividend reinvestment and 401 (k) plans [Member]
Long-Term Debt And Equity Financings [Line Items]
Issuances of common stock						$ 47,000,000	$ 51,000,000	$ 68,000,000
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized (in shares) | shares	7,500,000				7,500,000	7,500,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 1				$ 1	$ 1
Preferred stock, shares outstanding (in shares) | shares	0				0	0
Stock Issued						$ 0	0	0
Year One	$ 55,000,000				$ 55,000,000	$ 55,000,000
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, authorized (in shares) | shares	2,600,000				2,600,000	2,600,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0				$ 0	$ 0
Preferred stock, shares outstanding (in shares) | shares	0				0	0
Stock Issued						$ 0	0	0
Year One	$ 400,000,000				$ 400,000,000	400,000,000
Payments for Repurchase of Redeemable Preferred Stock						$ 13,000,000	0	$ 0
Common stock equity to capitalization ratio	54.00%				54.00%	54.00%
Ameren Illinois Company | 6.625% Series
Long-Term Debt And Equity Financings [Line Items]
Payments for Repurchase of Redeemable Preferred Stock						$ 12,000,000
Dividend rate on preferred shares, percentage						6.625%
Ameren Illinois Company | 7.75% Series
Long-Term Debt And Equity Financings [Line Items]
Payments for Repurchase of Redeemable Preferred Stock						$ 1,000,000
Dividend rate on preferred shares, percentage						7.75%
Ameren Missouri and Ameren Illinois
Long-Term Debt And Equity Financings [Line Items]
Bonds interest rate assumption	5.00%				5.00%	5.00%
Dividend rate on preferred shares, percentage						6.00%
Ameren Transmission Company of Illinois
Long-Term Debt And Equity Financings [Line Items]
Year One	$ 50,000,000				$ 50,000,000	$ 50,000,000
Ameren (parent)
Long-Term Debt And Equity Financings [Line Items]
Year One	0				0	0
Senior Secured Notes 1.75% Due 2028 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 450,000,000				$ 450,000,000	$ 450,000,000	0
Long-term debt interest rate	1.75%				1.75%	1.75%
Proceeds from Issuance of Unsecured Debt						$ 447,000,000
Senior Unsecured Notes 1.95% due 2027 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 500,000,000				$ 500,000,000	$ 500,000,000	0
Long-term debt interest rate	1.95%				1.95%	1.95%
Proceeds from Issuance of Unsecured Debt						$ 497,000,000
Senior Secured Notes 3.50% Due 2031 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 800,000,000				$ 800,000,000	$ 800,000,000	800,000,000
Long-term debt interest rate	3.50%				3.50%	3.50%
Proceeds from Issuance of Unsecured Debt						$ 793,000,000
Senior Unsecured Notes 2.70% due 2020 | Ameren (parent) | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount															$ 350,000,000
Long-term debt interest rate	2.70%				2.70%	2.70%
Senior Secured Notes 2.15% Due 2032 [Member] | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 525,000,000				$ 525,000,000	$ 525,000,000	0
Long-term debt interest rate	2.15%				2.15%	2.15%
Proceeds from issuance of secured debt						$ 521,000,000
First Mortgage Bonds, 2.95%, Due 2030 - $465 Issuance | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 465,000,000				$ 465,000,000	$ 465,000,000	465,000,000
Long-term debt interest rate	2.95%				2.95%	2.95%
Proceeds from issuance of secured debt						$ 462,000,000
5.00% Senior secured notes due 2020 | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount																$ 85,000,000
5.00% Senior secured notes due 2020 | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Long-term debt interest rate	5.00%				5.00%	5.00%
First Mortgage Bonds, 2.625%, Due 2051 - $550 Issuance | Union Electric Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 550,000,000				$ 550,000,000	$ 550,000,000	550,000,000
Long-term debt interest rate	2.625%				2.625%	2.625%
Proceeds from issuance of secured debt			$ 543,000,000
Number Of Acquired Wind Generation Facilities | windGenerationFacility	2				2	2
First Mortgage Bonds, 2.90%, $350 Million Due 2051 | Ameren Illinois Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 350,000,000				$ 350,000,000	$ 350,000,000	0
Long-term debt interest rate	2.90%				2.90%	2.90%
Proceeds from issuance of secured debt						$ 345,000,000
First Mortgage Bonds, 0.375%, $100 Million Due 2023 | Ameren Illinois Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 100,000,000				$ 100,000,000	$ 100,000,000	0
Long-term debt interest rate	0.375%				0.375%	0.375%
Proceeds from issuance of secured debt						$ 100,000,000
First Mortgage Bonds, 1.55%, Due 2030 | Ameren Illinois Company | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 375,000,000				$ 375,000,000	$ 375,000,000	375,000,000
Long-term debt interest rate	1.55%				1.55%	1.55%
Proceeds from issuance of secured debt						$ 371,000,000
Senior Unsecured Notes, 2.45% Due 2036 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 75,000,000				$ 75,000,000	$ 75,000,000	0
Long-term debt interest rate	2.45%				2.45%	2.45%
Proceeds from Issuance of Unsecured Debt						$ 75,000,000
Senior Unsecured Notes, 2.96%, Due 2052 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 95,000,000				$ 95,000,000	$ 95,000,000
Long-term debt interest rate	2.96%				2.96%	2.96%
Senior Unsecured Notes, 3.43%, Due 2050 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Debt instrument face amount	$ 450,000,000				$ 450,000,000	$ 450,000,000	$ 450,000,000
Year One	$ 50,000,000				$ 50,000,000	$ 50,000,000
Ratio of Indebtedness to Net Capital	0.70				0.70	0.70
Ratio of Indebtedness to Total Assets	0.10				0.10	0.10
Senior Unsecured Notes, 3.43%, Due 2050 | Ameren Transmission Company of Illinois | Secured Debt
Long-Term Debt And Equity Financings [Line Items]
Long-term debt interest rate	3.43%				3.43%	3.43%
Minimum | Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Common stock equity to capitalization ratio	30.00%				30.00%	30.00%
Subsequent Event | January 2022 Forward Sale
Long-Term Debt And Equity Financings [Line Items]
Forward Contract Indexed to Issuer's Equity, Indexed Shares | shares									200,000
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share | $ / shares		$ 88.10
Subsequent Event | Senior Unsecured Notes, 2.96%, Due 2052 | Ameren Transmission Company of Illinois | Unsecured Debt
Long-Term Debt And Equity Financings [Line Items]
Proceeds from Issuance of Unsecured Debt				$ 95,000,000

Long-Term Debt And Equity Fin_4

Long-Term Debt And Equity Financings (Schedule Of Long-Term Debt Outstanding) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Less: Maturities due within one year	$ (505,000,000)	$ (8,000,000)
Long-term Debt, Net	12,562,000,000	11,078,000,000
Ameren (parent)
Debt Instrument [Line Items]
Long-term debt, gross	2,550,000,000	1,600,000,000
Less: Unamortized discount and premium	(2,000,000)	(2,000,000)
Debt Issuance Costs, Net	(15,000,000)	(10,000,000)
Long-term Debt, Net	2,533,000,000	1,588,000,000
Union Electric Company
Debt Instrument [Line Items]
Long-term debt, gross	5,669,000,000	5,152,000,000
Less: Unamortized discount and premium	(12,000,000)	(12,000,000)
Debt Issuance Costs, Net	(38,000,000)	(36,000,000)
Less: Maturities due within one year	(55,000,000)	(8,000,000)
Long-term Debt, Net	5,564,000,000	5,096,000,000
Debt Securities, Held-to-maturity	248,000,000	256,000,000
Union Electric Company | City Of Bowling Green Agreement - Peno Creek Ct
Debt Instrument [Line Items]
Debt instrument face amount	8,000,000	16,000,000
Union Electric Company | Audrain County Agreement - Audrain County Ct
Debt Instrument [Line Items]
Debt instrument face amount	240,000,000	240,000,000
Ameren Illinois Company
Debt Instrument [Line Items]
Long-term debt, gross	4,438,000,000	3,988,000,000
Less: Unamortized discount and premium	(7,000,000)	(6,000,000)
Debt Issuance Costs, Net	(39,000,000)	(36,000,000)
Less: Maturities due within one year	(400,000,000)	0
Long-term Debt, Net	3,992,000,000	3,946,000,000
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
Long-term debt, gross	525,000,000	450,000,000
Debt Issuance Costs, Net	(2,000,000)	(2,000,000)
Less: Maturities due within one year	(50,000,000)	0
Long-term Debt, Net	473,000,000	448,000,000
Unsecured Debt | Ameren (parent) | Senior Unsecured Notes 2.50% Due 2024
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	450,000,000
Long-term debt interest rate	2.50%
Unsecured Debt | Ameren (parent) | Senior Unsecured Notes365 due 2026
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000	350,000,000
Long-term debt interest rate	3.65%
Unsecured Debt | Ameren (parent) | Senior Unsecured Notes 1.95% due 2027
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000	0
Long-term debt interest rate	1.95%
Unsecured Debt | Ameren (parent) | Senior Secured Notes 1.75% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	0
Long-term debt interest rate	1.75%
Unsecured Debt | Ameren (parent) | Senior Secured Notes 3.50% Due 2031
Debt Instrument [Line Items]
Debt instrument face amount	$ 800,000,000	800,000,000
Long-term debt interest rate	3.50%
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	$ 75,000,000	0
Long-term debt interest rate	2.45%
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	450,000,000
Secured Debt | Union Electric Company | Senior Secured Notes350 Due2024
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000	350,000,000
Long-term debt interest rate	3.50%
Secured Debt | Union Electric Company | Senior Secured Notes, 2.95%, Due 2027
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000	400,000,000
Long-term debt interest rate	2.95%
Secured Debt | Union Electric Company | First Mortgage Bonds, 3.50%, Due 2029 - $450 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 450,000,000	450,000,000
Long-term debt interest rate	3.50%
Secured Debt | Union Electric Company | First Mortgage Bonds, 2.95%, Due 2030 - $465 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 465,000,000	465,000,000
Long-term debt interest rate	2.95%
Secured Debt | Union Electric Company | Senior Secured Notes 2.15% Due 2032 [Member]
Debt Instrument [Line Items]
Debt instrument face amount	$ 525,000,000	0
Long-term debt interest rate	2.15%
Secured Debt | Union Electric Company | 5.50% Senior secured notes due 2034
Debt Instrument [Line Items]
Debt instrument face amount	$ 184,000,000	184,000,000
Long-term debt interest rate	5.50%
Secured Debt | Union Electric Company | 5.30% Senior secured notes due 2037
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000	300,000,000
Long-term debt interest rate	5.30%
Secured Debt | Union Electric Company | 8.45% Senior secured notes due 2039
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000	350,000,000
Long-term debt interest rate	8.45%
Secured Debt | Union Electric Company | 3.90% Senior secured notes due 2042
Debt Instrument [Line Items]
Debt instrument face amount	$ 485,000,000	485,000,000
Long-term debt interest rate	3.90%
Secured Debt | Union Electric Company | Senior Secured Notes, 3.65%, Due 2045
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000	400,000,000
Long-term debt interest rate	3.65%
Secured Debt | Union Electric Company | First Mortgage Bonds, 4.00%, Due 2048 - $425 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 425,000,000	425,000,000
Long-term debt interest rate	4.00%
Secured Debt | Union Electric Company | First Mortgage Bonds, 3.25%, Due 2049 - $330 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 330,000,000	330,000,000
Long-term debt interest rate	3.25%
Secured Debt | Union Electric Company | First Mortgage Bonds, 2.625%, Due 2051 - $550 Issuance
Debt Instrument [Line Items]
Debt instrument face amount	$ 550,000,000	550,000,000
Long-term debt interest rate	2.625%
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 2.70%, Due 2022
Debt Instrument [Line Items]
Debt instrument face amount	$ 400,000,000	400,000,000
Long-term debt interest rate	2.70%
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 0.375%, $100 Million Due 2023
Debt Instrument [Line Items]
Debt instrument face amount	$ 100,000,000	0
Long-term debt interest rate	0.375%
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 3.25%, Due 2025
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000	300,000,000
Long-term debt interest rate	3.25%
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.125% Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 60,000,000	60,000,000
Long-term debt interest rate	6.125%
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 3.80%, Due 2028
Debt Instrument [Line Items]
Debt instrument face amount	$ 430,000,000	430,000,000
Long-term debt interest rate	3.80%
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 1.55%, Due 2030
Debt Instrument [Line Items]
Debt instrument face amount	$ 375,000,000	375,000,000
Long-term debt interest rate	1.55%
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.70% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	$ 61,000,000	61,000,000
Long-term debt interest rate	6.70%
Secured Debt | Ameren Illinois Company | Senior Secured Notes 6.70% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	$ 42,000,000	42,000,000
Long-term debt interest rate	6.70%
Secured Debt | Ameren Illinois Company | Senior Secured Notes 4.80% Due 2043
Debt Instrument [Line Items]
Debt instrument face amount	$ 280,000,000	280,000,000
Long-term debt interest rate	4.80%
Secured Debt | Ameren Illinois Company | Senior Secured Notes 4.30% Due 2044
Debt Instrument [Line Items]
Debt instrument face amount	$ 250,000,000	250,000,000
Long-term debt interest rate	4.30%
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 4.15%, Due 2046
Debt Instrument [Line Items]
Debt instrument face amount	$ 490,000,000	490,000,000
Long-term debt interest rate	4.15%
Secured Debt | Ameren Illinois Company | Senior Secured Notes, 3.70%, Due 2047
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000	500,000,000
Long-term debt interest rate	3.70%
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 4.50%, Due 2049
Debt Instrument [Line Items]
Debt instrument face amount	$ 500,000,000	500,000,000
Long-term debt interest rate	4.50%
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 3.25%, Due 2050 - $300
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000	300,000,000
Long-term debt interest rate	3.25%
Secured Debt | Ameren Illinois Company | First Mortgage Bonds, 2.90%, $350 Million Due 2051
Debt Instrument [Line Items]
Debt instrument face amount	$ 350,000,000	0
Long-term debt interest rate	2.90%
Secured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
Long-term debt interest rate	3.43%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1992 Series due 2022
Debt Instrument [Line Items]
Debt instrument face amount	$ 47,000,000	47,000,000
Long-term debt interest rate	1.60%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series A due 2033
Debt Instrument [Line Items]
Debt instrument face amount	$ 60,000,000	60,000,000
Long-term debt interest rate	2.90%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series B due 2033
Debt Instrument [Line Items]
Debt instrument face amount	$ 50,000,000	50,000,000
Long-term debt interest rate	2.90%
Environmental Improvement And Pollution Control Revenue Bonds | Union Electric Company | 1998 Series C due 2033
Debt Instrument [Line Items]
Debt instrument face amount	$ 50,000,000	$ 50,000,000
Long-term debt interest rate	2.75%

Long-Term Debt And Equity Fin_5

Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
2022	$ 505,000,000
2023	340,000,000
2024	850,000,000
2025	300,000,000
2026	350,000,000
Thereafter	10,837,000,000
Total	13,182,000,000
Ameren (parent)
Debt Instrument [Line Items]
2022	0
2023	0
2024	450,000,000
2025	0
2026	350,000,000
Thereafter	1,750,000,000
Total	2,550,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	17,000,000
Union Electric Company
Debt Instrument [Line Items]
2022	55,000,000
2023	240,000,000
2024	350,000,000
2025	0
2026	0
Thereafter	5,024,000,000
Total	5,669,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	50,000,000
Ameren Illinois Company
Debt Instrument [Line Items]
2022	400,000,000
2023	100,000,000
2024	0
2025	300,000,000
2026	0
Thereafter	3,638,000,000
Total	4,438,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	46,000,000
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
2022	50,000,000
2023	0
2024	50,000,000
2025	0
2026	0
Thereafter	425,000,000
Total	525,000,000
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	2,000,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036
Debt Instrument [Line Items]
Debt instrument face amount	75,000,000	$ 0
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036 | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Thereafter	30,000,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 2.45% Due 2036 | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Thereafter	45,000,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050
Debt Instrument [Line Items]
2022	50,000,000
Debt instrument face amount	450,000,000	$ 450,000,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
2022	49,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
2024	49,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Four
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Five
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Six
Debt Instrument [Line Items]
Thereafter	49,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Seven
Debt Instrument [Line Items]
Thereafter	76,500,000
Unsecured Debt | Ameren Transmission Company of Illinois | Senior Unsecured Notes, 3.43%, Due 2050 | Debt Instrument, Redemption, Period Eight
Debt Instrument [Line Items]
Thereafter	$ 76,500,000

Long-Term Debt And Equity Fin_6

Long-Term Debt And Equity Financings (Schedule Of Outstanding Preferred Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	0
Preferred stock, voluntary liquidation (in dollars per share)	$ 105.50
Preferred stock, par value (in dollars per share)	$ 0.01
Preferred stock, authorized (in shares)	100,000,000
Union Electric Company and Ameren Illinois
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, issued (in shares)	$ 129	$ 142
Union Electric Company
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	0
Preferred stock, issued (in shares)	$ 80	80
Preferred stock, par value (in dollars per share)	$ 1
Preferred stock, authorized (in shares)	7,500,000
Union Electric Company | $3.50 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	130,000
Preferred stock, redemption price per share (in dollars per share)	$ 110
Preferred stock, issued (in shares)	$ 13	13
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 3.50
Union Electric Company | $3.70 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	40,000
Preferred stock, redemption price per share (in dollars per share)	$ 104.75
Preferred stock, issued (in shares)	$ 4	4
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 3.70
Union Electric Company | $4.00 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	150,000
Preferred stock, redemption price per share (in dollars per share)	$ 105.625
Preferred stock, issued (in shares)	$ 15	15
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 4
Union Electric Company | $4.30 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	40,000
Preferred stock, redemption price per share (in dollars per share)	$ 105
Preferred stock, issued (in shares)	$ 4	4
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 4.30
Union Electric Company | $4.50 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	213,595
Preferred stock, redemption price per share (in dollars per share)	$ 110
Preferred stock, issued (in shares)	$ 21	21
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 4.50
Union Electric Company | $4.56 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	200,000
Preferred stock, redemption price per share (in dollars per share)	$ 102.47
Preferred stock, issued (in shares)	$ 20	20
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 4.56
Union Electric Company | $4.75 Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	20,000
Preferred stock, redemption price per share (in dollars per share)	$ 102.176
Preferred stock, issued (in shares)	$ 2	2
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 4.75
Union Electric Company | $5.50 Series A
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	14,000
Preferred stock, redemption price per share (in dollars per share)	$ 110
Preferred stock, issued (in shares)	$ 1	1
Dividend rate on preferred shares, per-dollar amount (in dollars per share)	$ 5.50
Union Electric Company | Par Value $100
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, par value (in dollars per share)	$ 100
Preferred stock, authorized (in shares)	25,000,000
Ameren Illinois Company
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	0
Preferred stock, issued (in shares)	$ 49	62
Preferred stock, par value (in dollars per share)	$ 0
Preferred stock, authorized (in shares)	2,600,000
Ameren Illinois Company | 4.00% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	144,275
Preferred stock, redemption price per share (in dollars per share)	$ 101
Preferred stock, issued (in shares)	$ 14	14
Dividend rate on preferred shares, percentage	4.00%
Ameren Illinois Company | 4.08% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	45,224
Preferred stock, redemption price per share (in dollars per share)	$ 103
Preferred stock, issued (in shares)	$ 5	5
Dividend rate on preferred shares, percentage	4.08%
Ameren Illinois Company | 4.20% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	23,655
Preferred stock, redemption price per share (in dollars per share)	$ 104
Preferred stock, issued (in shares)	$ 2	2
Dividend rate on preferred shares, percentage	4.20%
Ameren Illinois Company | 4.25% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	50,000
Preferred stock, redemption price per share (in dollars per share)	$ 102
Preferred stock, issued (in shares)	$ 5	5
Dividend rate on preferred shares, percentage	4.25%
Ameren Illinois Company | 4.26% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	16,621
Preferred stock, redemption price per share (in dollars per share)	$ 103
Preferred stock, issued (in shares)	$ 2	2
Dividend rate on preferred shares, percentage	4.26%
Ameren Illinois Company | 4.42% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	16,190
Preferred stock, redemption price per share (in dollars per share)	$ 103
Preferred stock, issued (in shares)	$ 2	2
Dividend rate on preferred shares, percentage	4.42%
Ameren Illinois Company | 4.70% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	18,429
Preferred stock, redemption price per share (in dollars per share)	$ 104.30
Preferred stock, issued (in shares)	$ 2	2
Dividend rate on preferred shares, percentage	4.70%
Ameren Illinois Company | 4.90% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	73,825
Preferred stock, redemption price per share (in dollars per share)	$ 102
Preferred stock, issued (in shares)	$ 7	7
Dividend rate on preferred shares, percentage	0.049%
Ameren Illinois Company | 4.92% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	49,289
Preferred stock, redemption price per share (in dollars per share)	$ 103.50
Preferred stock, issued (in shares)	$ 5	5
Dividend rate on preferred shares, percentage	4.92%
Ameren Illinois Company | 5.16% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, shares outstanding (in shares)	50,000
Preferred stock, redemption price per share (in dollars per share)	$ 102
Preferred stock, issued (in shares)	$ 5	5
Dividend rate on preferred shares, percentage	5.16%
Ameren Illinois Company | 6.625% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, redemption price per share (in dollars per share)	$ 100
Preferred stock, issued (in shares)	$ 0	12
Dividend rate on preferred shares, percentage	6.625%
Ameren Illinois Company | 7.75% Series
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, redemption price per share (in dollars per share)	$ 100
Preferred stock, issued (in shares)	$ 0	$ 1
Dividend rate on preferred shares, percentage	7.75%
Ameren Illinois Company | Par Value $100
Long-Term Debt And Equity Financings [Line Items]
Preferred stock, par value (in dollars per share)	$ 100
Preferred stock, authorized (in shares)	2,000,000

Long-Term Debt and Equity Fin_7

Long-Term Debt and Equity Financings (Schedule of Required and Actual Debt Ratios) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Union Electric Company
Debt Instrument [Line Items]
Bonds Issuable Based On Coverage Ratio	$ 4,834
Preferred Stock Issuable Based On Coverage Ratio	3,418
Retired Bond Capacity	$ 2,437
Union Electric Company | Actual Interest Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	3.2
Dividend Coverage Ratio	152.4
Ameren Illinois Company
Debt Instrument [Line Items]
Bonds Issuable Based On Coverage Ratio	$ 7,697
Preferred Stock Issuable Based On Coverage Ratio	203
Retired Bond Capacity	$ 643
Ameren Illinois Company | Actual Interest Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	7.3
Dividend Coverage Ratio	3.5
Minimum | Union Electric Company | Required Dividend Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	2
Dividend Coverage Ratio	2.5
Minimum | Ameren Illinois Company | Required Dividend Coverage Ratio
Debt Instrument [Line Items]
Interest Coverage Ratio	2
Dividend Coverage Ratio	1.5

Other Income, Net (Other Income

Other Income, Net (Other Income And Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 43	$ 32	$ 28
Interest income on industrial development revenue bonds	25	25	25
Other interest income	2	4	8
Non-service cost components of net periodic benefit income	136	116	90
Miscellaneous income	22	13	6
Donations	(9)	(25)	(12)
Miscellaneous expense	(17)	(14)	(15)
Total other income, net	202	151	130
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	26	19	19
Interest income on industrial development revenue bonds	25	25	25
Other interest income	1	1	1
Non-service cost components of net periodic benefit income	55	46	18
Miscellaneous income	3	4	5
Donations	(4)	(12)	(3)
Miscellaneous expense	(7)	(7)	(7)
Total other income, net	99	76	58
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	(7)	(4)	29
Union Electric Company | Final Rate Order | Electric
Other Nonoperating Income (Expense) [Line Items]
Donations		(8)
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	17	13	9
Other interest income	1	3	6
Non-service cost components of net periodic benefit income	55	48	47
Miscellaneous income	6	6	3
Donations	(5)	(5)	(5)
Miscellaneous expense	(8)	(6)	(7)
Total other income, net	$ 66	$ 59	$ 53

Derivative Financial Instrume_3

Derivative Financial Instruments (Open Gross Derivative Volumes By Commodity Type) (Details) lb in Thousands, gal in Millions, MWh in Millions, MMBTU in Millions	12 Months Ended
	Dec. 31, 2021MMBTUMWhlbgal	Dec. 31, 2020MMBTUMWhlbgal
Fuel Oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	30	43
Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	179	147
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	12	13
Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	586	365
Union Electric Company | Fuel Oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	30	43
Union Electric Company | Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	35	33
Union Electric Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	6	6
Union Electric Company | Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	586	365
Ameren Illinois Company | Fuel Oils
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | gal	0	0
Ameren Illinois Company | Natural gas
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	144	114
Ameren Illinois Company | Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh	6	7
Ameren Illinois Company | Uranium
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | lb	0	0

Derivative Financial Instrume_4

Derivative Financial Instruments (Derivative Instruments Carrying Value) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative assets	$ 90	$ 22
Derivative liabilities	202	221
Fuel Oils | Other current assets
Derivative [Line Items]
Derivative assets	8	2
Fuel Oils | Other assets
Derivative [Line Items]
Derivative assets	5	0
Fuel Oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	7
Fuel Oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	0	2
Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	35	9
Natural gas | Other assets
Derivative [Line Items]
Derivative assets	18	4
Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	8	2
Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	3	1
Power | Other current assets
Derivative [Line Items]
Derivative assets	23	7
Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	59	20
Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	131	189
Uranium | Other assets
Derivative [Line Items]
Derivative assets	1	0
Uranium | Other current liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Union Electric Company
Derivative [Line Items]
Derivative assets	49	12
Derivative liabilities	77	21
Union Electric Company | Fuel Oils | Other current assets
Derivative [Line Items]
Derivative assets	8	2
Union Electric Company | Fuel Oils | Other assets
Derivative [Line Items]
Derivative assets	5	0
Union Electric Company | Fuel Oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	7
Union Electric Company | Fuel Oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	0	2
Union Electric Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	7	1
Union Electric Company | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	5	2
Union Electric Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Union Electric Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Union Electric Company | Power | Other current assets
Derivative [Line Items]
Derivative assets	23	7
Union Electric Company | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	50	3
Union Electric Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	23	8
Union Electric Company | Uranium | Other assets
Derivative [Line Items]
Derivative assets	1	0
Union Electric Company | Uranium | Other current liabilities
Derivative [Line Items]
Derivative liabilities	1	0
Ameren Illinois Company
Derivative [Line Items]
Derivative assets	41	10
Derivative liabilities	125	200
Ameren Illinois Company | Fuel Oils | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Fuel Oils | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Fuel Oils | Other current liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Fuel Oils | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Natural gas | Other current assets
Derivative [Line Items]
Derivative assets	28	8
Ameren Illinois Company | Natural gas | Other assets
Derivative [Line Items]
Derivative assets	13	2
Ameren Illinois Company | Natural gas | Other current liabilities
Derivative [Line Items]
Derivative liabilities	6	1
Ameren Illinois Company | Natural gas | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	2	1
Ameren Illinois Company | Power | Other current assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Power | Other current liabilities
Derivative [Line Items]
Derivative liabilities	9	17
Ameren Illinois Company | Power | Other deferred credits and liabilities
Derivative [Line Items]
Derivative liabilities	108	181
Ameren Illinois Company | Uranium | Other assets
Derivative [Line Items]
Derivative assets	0	0
Ameren Illinois Company | Uranium | Other current liabilities
Derivative [Line Items]
Derivative liabilities	$ 0	$ 0

Derivative Financial Instrume_5

Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) - Not Designated As Hedging Instrument - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 90	$ 22
Derivative Liability, Fair Value, Gross Liability	202	221
Derivative, Collateral, Obligation to Return Securities	19
Derivative, Collateral, Right to Reclaim Securities	19
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	47
Derivative Asset	71
Derivative Liability	136
Union Electric Company
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	49	12
Derivative Liability, Fair Value, Gross Liability	77	21
Derivative, Collateral, Obligation to Return Securities	15
Derivative, Collateral, Right to Reclaim Securities	15
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	47
Derivative Asset	34
Derivative Liability	15
Ameren Illinois Company
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	41	10
Derivative Liability, Fair Value, Gross Liability	125	$ 200
Derivative, Collateral, Obligation to Return Securities	4
Derivative, Collateral, Right to Reclaim Securities	4
Derivative Asset, Collateral, Obligation to Return Cash, Offset	0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset	0
Derivative Asset	37
Derivative Liability	$ 121

Derivative Financial Instrume_6

Derivative Financial Instruments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Credit Derivatives [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	$ 77
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	61
Union Electric Company
Credit Derivatives [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	36
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	23
Ameren Illinois Company
Credit Derivatives [Line Items]
Credit Derivative, Maximum Exposure, Undiscounted	41
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 38

Fair Value Measurements (Schedu

Fair Value Measurements (Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	$ 1,152	$ 977
Assets	1,242	999
Excluded receivables, payables, and accrued income, net	7	5
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	824	680
Assets	848	682
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	328	297
Assets	373	306
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Assets	21	11
Power | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	13	5
Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	90	22
Derivative liabilities	202	221
Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	24	2
Derivative liabilities	45	14
Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	45	9
Derivative liabilities	7	2
Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	21	11
Derivative liabilities	150	205
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	1,201	989
Union Electric Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	847	682
Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	340	300
Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	14	7
Union Electric Company | Fuel Oils
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	13	2
Derivative liabilities	0	9
Union Electric Company | Fuel Oils | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	13	0
Derivative liabilities	0	6
Union Electric Company | Fuel Oils | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Fuel Oils | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	2
Derivative liabilities	0	3
Union Electric Company | Natural gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	12	3
Derivative liabilities	3	1
Union Electric Company | Natural gas | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Natural gas | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	12	3
Derivative liabilities	2	1
Union Electric Company | Natural gas | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	1	0
Union Electric Company | Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	23	7
Derivative liabilities	73	11
Union Electric Company | Power | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	10	2
Derivative liabilities	45	8
Union Electric Company | Power | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Power | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	13	5
Derivative liabilities	28	3
Union Electric Company | Uranium
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1	0
Derivative liabilities	1	0
Union Electric Company | Uranium | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Uranium | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Union Electric Company | Uranium | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1	0
Derivative liabilities	1	0
Union Electric Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	49	12
Derivative liabilities	77	21
Union Electric Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	23	2
Derivative liabilities	45	14
Union Electric Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	12	3
Derivative liabilities	2	1
Union Electric Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	14	7
Derivative liabilities	30	6
Union Electric Company | Equity securities | U.S. large capitalization
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	824	680
Union Electric Company | Equity securities | U.S. large capitalization | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	824	680
Union Electric Company | Equity securities | U.S. large capitalization | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Equity securities | U.S. large capitalization | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt securities | U.S. Treasury and agency securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	141	115
Union Electric Company | Debt securities | U.S. Treasury and agency securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt securities | U.S. Treasury and agency securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	141	115
Union Electric Company | Debt securities | U.S. Treasury and agency securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt securities | Corporate bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	131	115
Union Electric Company | Debt securities | Corporate bonds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt securities | Corporate bonds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	131	115
Union Electric Company | Debt securities | Corporate bonds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt securities | Diversified credit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	56	67
Union Electric Company | Debt securities | Diversified credit | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Union Electric Company | Debt securities | Diversified credit | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	56	67
Union Electric Company | Debt securities | Diversified credit | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Nuclear Decommissioning Trust Fund	0	0
Ameren Illinois Company | Natural gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	41	10
Derivative liabilities	8	2
Ameren Illinois Company | Natural gas | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	1	0
Derivative liabilities	0	0
Ameren Illinois Company | Natural gas | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	33	6
Derivative liabilities	5	1
Ameren Illinois Company | Natural gas | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative assets	7	4
Derivative liabilities	3	1
Ameren Illinois Company | Power
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	117	198
Ameren Illinois Company | Power | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Power | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Power | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	117	198
Ameren Illinois Company | Commodity Contract
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	125	200
Ameren Illinois Company | Commodity Contract | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Ameren Illinois Company | Commodity Contract | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	5	1
Ameren Illinois Company | Commodity Contract | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative liabilities	$ 120	$ 199

Fair Value Measurements (Sche_2

Fair Value Measurements (Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy) (Details) - Power - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	$ (132)	$ (196)	$ (211)
Included in regulatory assets/liabilities	69	23
Settlements	5	8
Change in unrealized gains (losses) related to assets/liabilities held at December 31	51	10
Union Electric Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	(15)	2	13
Included in regulatory assets/liabilities	(1)	15
Settlements	16	26
Change in unrealized gains (losses) related to assets/liabilities held at December 31	(14)	1
Ameren Illinois Company
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis with Unobservable Inputs	(117)	(198)	$ (224)
Included in regulatory assets/liabilities	70	8
Settlements	11	18
Change in unrealized gains (losses) related to assets/liabilities held at December 31	$ 65	$ 9

Fair Value Measurements (Sche_3

Fair Value Measurements (Schedule of Valuation Process and Unobservable Inputs) (Details) - Power $ in Millions	Dec. 31, 2021USD ($)$ / MWh$ / MMBTU	Dec. 31, 2020USD ($)$ / MWh$ / MMBTU
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets | $	$ 13	$ 5
Derivative Liability | $	$ (145)	$ (201)
Measurement Input, Commodity Forward Price | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	32	23
Measurement Input, Commodity Forward Price | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	55	37
Measurement Input, Commodity Forward Price | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	40	29
Measurement Input, Nodal Basis | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	(14)	(6)
Measurement Input, Nodal Basis | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0	0
Measurement Input, Nodal Basis | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	(2)	(2)
Measurement Input, Commodity Future Price | Minimum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input | $ / MMBTU	0	2
Measurement Input, Commodity Future Price | Maximum | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input | $ / MMBTU	0	6
Measurement Input, Commodity Future Price | Weighted Average | Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input | $ / MMBTU	0	3

Fair Value Measurements (Sche_4

Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Financial Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	$ 155	$ 301	$ 176	$ 107
Short-term debt	545	490
Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	8	145	39	8
Advances to money pool	0	139
Short-term debt	165	0
Debt Issuance Costs, Net	38	36
Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	133	147	$ 125	$ 80
Short-term debt	103	0
Borrowings from money pool	0	19
Debt Issuance Costs, Net	39	36
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	155	301
Investments in industrial development revenue bonds	248	256
Short-term debt	545	490
Long-term debt (including current portion)	13,067	11,086
Debt Issuance Costs, Net	94	84
Carrying Amount | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	8	145
Advances to money pool		139
Investments in industrial development revenue bonds	248	256
Short-term debt	165
Long-term debt (including current portion)	5,619	5,104
Debt Issuance Costs, Net	38	36
Carrying Amount | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	133	147
Short-term debt	103
Long-term debt (including current portion)	4,392	3,946
Borrowings from money pool		19
Debt Issuance Costs, Net	39	36
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	155	301
Investments, Fair Value Disclosure	248	256
Short-term Debt, Fair Value	545	490
Long-term Debt, Fair Value	14,521	13,315
Fair Value | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	155	301
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	0	0
Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	248	256
Short-term Debt, Fair Value	545	490
Long-term Debt, Fair Value	13,930	12,778
Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0	0
Long-term Debt, Fair Value	591	537
Fair Value | Union Electric Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	8	145
Advances to money pool		139
Investments, Fair Value Disclosure	248	256
Short-term Debt, Fair Value	165
Long-term Debt, Fair Value	6,321	6,160
Fair Value | Union Electric Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	8	145
Advances to money pool		0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	0	0
Fair Value | Union Electric Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Advances to money pool		139
Investments, Fair Value Disclosure	248	256
Short-term Debt, Fair Value	165
Long-term Debt, Fair Value	6,321	6,160
Fair Value | Union Electric Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Advances to money pool		0
Investments, Fair Value Disclosure	0	0
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	0	0
Fair Value | Ameren Illinois Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	133	147
Short-term Debt, Fair Value	103
Long-term Debt, Fair Value	4,971	4,822
Borrowings from money pool		19
Fair Value | Ameren Illinois Company | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	133	147
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	0	0
Borrowings from money pool		0
Fair Value | Ameren Illinois Company | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	103
Long-term Debt, Fair Value	4,971	4,822
Borrowings from money pool		19
Fair Value | Ameren Illinois Company | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash, cash equivalents, and restricted cash	0	0
Short-term Debt, Fair Value	0
Long-term Debt, Fair Value	$ 0	0
Borrowings from money pool		$ 0

Callaway Energy Center (Narrati

Callaway Energy Center (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		$ 85	$ 65
Accidental Outage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Amount of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage		4.5
Non-radiation event
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		33
Non-radiation event | Subsequent Event
Nuclear Waste Matters [Line Items]
Proceeds from Insurance Settlement, Investing Activities	$ 17
Union Electric Company
Nuclear Waste Matters [Line Items]
Miscellaneous accounts receivable		$ 71	$ 36
Frequency of Decommissioning Cost Study		3 years
Union Electric Company | Minimum | Nuclear Decommissioning Trust Fund
Nuclear Waste Matters [Line Items]
Trust Fund Investments, Target Allocation Percentage		60.00%
Union Electric Company | Maximum | Nuclear Decommissioning Trust Fund
Nuclear Waste Matters [Line Items]
Trust Fund Investments, Target Allocation Percentage		70.00%
Union Electric Company | Nuclear Plant
Nuclear Waste Matters [Line Items]
Estimated Nuclear Generator Repairs		$ 60
Annual decommissioning costs included in costs of service		$ 7

Callaway Energy Center (Proceed

Callaway Energy Center (Proceeds From The Sale Of Investments And Related Gross Realized Gains And Losses In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Nuclear Waste Matters [Line Items]
Proceeds from sales and maturities	$ 439	$ 183	$ 260
Union Electric Company
Nuclear Waste Matters [Line Items]
Proceeds from sales and maturities	439	183	260
Gross realized gains	32	10	10
Gross realized losses	$ 6	$ 3	$ 2

Callaway Energy Center (Fair Va

Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 320
Total cash, cash equivalents, and restricted cash	155	$ 301	$ 176	$ 107
Fair Value	1,159	982
Cash and cash equivalents	8	139
Union Electric Company
Nuclear Waste Matters [Line Items]
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost	515	475
Total cash, cash equivalents, and restricted cash	8	145	$ 39	$ 8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	650	516
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	9
Fair Value	1,159	982
Cash and cash equivalents	0	136
Debt, Equity, Marketable, And Other Securities, Available-For-Sale	1,159	982
Union Electric Company | Debt securities
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	320	272
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	10	25
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2	0
Fair Value	328	297
Union Electric Company | Equity securities
Nuclear Waste Matters [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	188	198
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	640	491
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	4	9
Equity Securities, FV-NI	824	680
Union Electric Company | Cash and cash equivalents
Nuclear Waste Matters [Line Items]
Marketable Securities	4	4
Total cash, cash equivalents, and restricted cash	0	0
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents	0	0
Cash and cash equivalents	4	4
Union Electric Company | Other Debt And Equity Securities
Nuclear Waste Matters [Line Items]
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Cost Basis	3	1
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Gain, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Loss, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Fair Value	$ 3	$ 1

Callaway Energy Center (Cost an

Callaway Energy Center (Cost and Fair Values of Investments In Debt Securities in Nuclear Decommissioning Trust Fund According to Contractual Maturities) (Details) $ in Millions	Dec. 31, 2021USD ($)
Nuclear Waste Matters [Abstract]
Cost, Less than 5 years	$ 155
Cost, 5 years to 10 years	71
Cost, Due after 10 years	94
Cost, Total	320
Fair Value, Less than 5 years	156
Fair Value, 5 years to 10 years	72
Fair Value, Due after 10 years	100
Fair Value, Total	$ 328

Callaway Energy Center (Insuran

Callaway Energy Center (Insurance Disclosure) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
Nuclear Waste Matters [Line Items]
Number Of Years The Limit Of Liability And The Maximum Potential Annual Payments Are Adjusted	five years
Number of weeks of coverage after the first twelve weeks of an outage	1
Number Of Additional Weeks After Initial Indemnity Coverage For Power Outage	1.365
Public Liability And Nuclear Worker Liability - American Nuclear Insurers
Nuclear Waste Matters [Line Items]
Maximum Coverages	$ 450
Maximum Assessments for Single Incidents	0
Public Liability And Nuclear Worker Liability - Pool Participation
Nuclear Waste Matters [Line Items]
Maximum Coverages	13,073
Maximum Assessments for Single Incidents	138
Threshold Amount For which a Retrospective Assessment For a Covered loss is necessary	450
Maximum Annual Payment Per Incident At Licensed Commercial Nuclear Reactor	21
Public Liability And Nuclear Worker Liability
Nuclear Waste Matters [Line Items]
Maximum Coverages	13,523
Maximum Assessments for Single Incidents	138
Property Damage - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Maximum Coverages	3,200
Maximum Assessments for Single Incidents	25
Replacement Power - Nuclear Electric Insurance Ltd
Nuclear Waste Matters [Line Items]
Maximum Coverages	490
Maximum Assessments for Single Incidents	7
Amount of Weekly Indemnity Coverage Commencing Twelve Weeks After Power Outage	4.5
Amount of additional weekly indemnity coverage commencing after initial indemnity coverage	3.6
Amount Of Weekly Indemnity Coverage Thereafter Not Exceeding Policy Limit	490
Sub-limit of for Non-Nuclear Events	328
Radiation Event
Nuclear Waste Matters [Line Items]
Maximum Coverages	2,700
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period	3,200
Non-radiation event
Nuclear Waste Matters [Line Items]
Maximum Coverages	2,300
Aggregate nuclear power industry insurance policy limit for losses from terrorist attacks within twelve month period	1,800
Property Damage European Mutual Association for Nuclear Insurance
Nuclear Waste Matters [Line Items]
Maximum Coverages	$ 490

Retirement Benefits (Narrative)

Retirement Benefits (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021USD ($)bond	Dec. 31, 2020USD ($)	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ 717	$ 249
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation, Change in Discount Rate		0.25%
Number of high-quality corporate bonds | bond		820
Collateralized loan percentage compared to asset's market value		102.00%
Securities Loaned		$ 374	365
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ 288	$ 0
Expected return on plan assets		6.50%	7.00%	7.00%
Pension Benefits | Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	6.50%

Retirement Benefits (Summary Of

Retirement Benefits (Summary Of Benefit Liability Recorded) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Noncurrent asset	$ (717)	$ (249)
Union Electric Company
Defined Benefit Plan Disclosure [Line Items]
Noncurrent asset	(189)	(25)
Ameren Illinois Company
Defined Benefit Plan Disclosure [Line Items]
Noncurrent asset	$ (416)	$ (210)

Retirement Benefits (Funded Sta

Retirement Benefits (Funded Status Of Benefit Plans And Amounts Included In Regulatory Assets And OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in plan assets:
Funded status – surplus	$ (717)	$ (249)
Accrued benefit asset at December 31	(717)	(249)
Amounts recognized in the balance sheet consist of:
Noncurrent asset	(756)	(288)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation at end of year	5,174	5,213
Change in benefit obligation:
Net benefit obligation at beginning of year	5,510	4,967
Service cost	134	110	$ 88
Interest cost	152	174	187
Participant contributions	0	0
Actuarial (gain) loss	(82)	508
Benefits paid	(257)	(249)
Net benefit obligation at end of year	5,457	5,510	4,967
Change in plan assets:
Fair value of plan assets at beginning of year	5,510	4,564
Actual return on plan assets	432	1,143
Employer contributions	60	52	23
Participant contributions	0	0
Benefits paid	(257)	(249)
Fair value of plan assets at end of year	5,745	5,510	4,564
Funded status – surplus	(288)	0
Accrued benefit asset at December 31	(288)	0
Amounts recognized in the balance sheet consist of:
Noncurrent asset	(327)	(39)
Liability, Defined Benefit Plan, Current	2	2
Liability, Defined Benefit Plan, Noncurrent	37	37
Amounts recognized in regulatory assets consist of:
Net actuarial gain	(415)	(138)
Prior service credit	0	0
Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial (gain) loss	(8)	5
Total	(423)	(133)
Postretirement Benefits
Change in benefit obligation:
Net benefit obligation at beginning of year	1,204	1,110
Service cost	23	19	18
Interest cost	33	39	43
Participant contributions	9	8
Actuarial (gain) loss	(80)	91
Benefits paid	(60)	(63)
Net benefit obligation at end of year	1,129	1,204	1,110
Change in plan assets:
Fair value of plan assets at beginning of year	1,453	1,297
Actual return on plan assets	154	209
Employer contributions	2	2	3
Participant contributions	9	8
Benefits paid	(60)	(63)
Fair value of plan assets at end of year	1,558	1,453	$ 1,297
Funded status – surplus	(429)	(249)
Accrued benefit asset at December 31	(429)	(249)
Amounts recognized in the balance sheet consist of:
Noncurrent asset	(429)	(249)
Liability, Defined Benefit Plan, Current	0	0
Liability, Defined Benefit Plan, Noncurrent	0	0
Amounts recognized in regulatory assets consist of:
Net actuarial gain	(343)	(200)
Prior service credit	(33)	(37)
Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial (gain) loss	1	6
Total	$ (375)	$ (231)

Retirement Benefits (Assumption

Retirement Benefits (Assumptions Used To Determine Benefit Obligations) (Details)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate at measurement date	3.00%	2.75%
Increase in future compensation	3.50%	3.50%
Cash balance pension plan interest crediting rate	5.00%	5.00%	5.00%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate at measurement date	3.00%	2.75%
Increase in future compensation	3.50%	3.50%
Medical cost trend rate (initial)	5.00%	5.00%	5.00%
Medical cost trend rate (ultimate)	5.00%	5.00%	5.00%
Postretirement Health Coverage
Defined Benefit Plan Disclosure [Line Items]
Medical cost trend rate (initial)	2.50%	3.00%
Medical cost trend rate (ultimate)	3.00%

Retirement Benefits (Cash Contr

Retirement Benefits (Cash Contributions Made To Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	$ 60	$ 52	$ 23
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	2	2	3
Union Electric Company | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	22	17	3
Union Electric Company | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	1	1	1
Ameren Illinois Company | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	28	27	19
Ameren Illinois Company | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	1	1	1
Other | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	10	8	1
Other | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Cash contributions to benefit plans	$ 0	$ 0	$ 1

Retirement Benefits (Target All

Retirement Benefits (Target Allocation Of The Plans' Asset Categories) (Details)	Dec. 31, 2021	Dec. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	100.00%	100.00%
Pension Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	3.00%	1.00%
Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	58.00%	59.00%
Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	23.00%	26.00%
Pension Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	9.00%	9.00%
Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	15.00%	15.00%
Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	11.00%	9.00%
Pension Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	35.00%	36.00%
Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	4.00%	4.00%
Pension Benefits | Private equity
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	1.00%	1.00%
Pension Benefits | Diversified credit
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	1.00%	1.00%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	100.00%	100.00%
Postretirement Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	3.00%	3.00%
Postretirement Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	62.00%	64.00%
Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	30.00%	31.00%
Postretirement Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	9.00%	8.00%
Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	13.00%	15.00%
Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	10.00%	10.00%
Postretirement Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	35.00%	33.00%
Minimum | Pension Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	45.00%
Minimum | Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	11.00%
Minimum | Pension Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Minimum | Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	9.00%
Minimum | Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	7.00%
Minimum | Pension Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	35.00%
Minimum | Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Pension Benefits | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Pension Benefits | Diversified credit
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Postretirement Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Postretirement Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	55.00%
Minimum | Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	23.00%
Minimum | Postretirement Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Minimum | Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	9.00%
Minimum | Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Minimum | Postretirement Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	33.00%
Maximum | Pension Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Maximum | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	55.00%
Maximum | Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	21.00%
Maximum | Pension Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	13.00%
Maximum | Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	19.00%
Maximum | Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	17.00%
Maximum | Pension Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	45.00%
Maximum | Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
Maximum | Pension Benefits | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Maximum | Pension Benefits | Diversified credit
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
Maximum | Postretirement Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	7.00%
Maximum | Postretirement Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	65.00%
Maximum | Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	33.00%
Maximum | Postretirement Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	13.00%
Maximum | Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	19.00%
Maximum | Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%
Maximum | Postretirement Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	43.00%

Retirement Benefits (Fair Value

Retirement Benefits (Fair Value Of Plan Assets Utilizing Fair Value Hierarchy) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 5,745	$ 5,510	$ 4,564
Pension Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	947	886
Pension Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,056	1,889
Pension Benefits | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,905	2,921
Pension Benefits | Includes Medical Benefit Component Under Section401 H And Excludes Receivables Related To Pending Security Sales [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,908	5,696
Pension Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	116	145
Pension Benefits | Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Cash and cash equivalents | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	116	145
Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,381	1,511
Pension Benefits | U.S. large-capitalization | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | U.S. large-capitalization | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | U.S. large-capitalization | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,381	1,511
Pension Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	558	513
Pension Benefits | U.S. small- and mid-capitalization | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	558	513
Pension Benefits | U.S. small- and mid-capitalization | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | U.S. small- and mid-capitalization | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	903	867
Pension Benefits | International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	372	375
Pension Benefits | International | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | International | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	531	492
Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	621	546
Pension Benefits | Global | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Global | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Global | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	621	546
Pension Benefits | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	572	523
Pension Benefits | Corporate bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	545	506
Pension Benefits | Corporate bonds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27	17
Pension Benefits | Municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50	50
Pension Benefits | Municipal bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	50	50
Pension Benefits | Municipal bonds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | U.S. Treasury and agency securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,450	1,328
Pension Benefits | U.S. Treasury and agency securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	3
Pension Benefits | U.S. Treasury and agency securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,450	1,325
Pension Benefits | U.S. Treasury and agency securities | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28	3
Pension Benefits | Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	(5)
Pension Benefits | Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	8
Pension Benefits | Other | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	228	208
Pension Benefits | Real estate | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Real estate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Real estate | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	228	208
Pension Benefits | Private equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	2
Pension Benefits | Private equity | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Private equity | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Benefits | Private equity | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	2
Pension Benefits | Medical benefit assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(234)	(219)
Pension Benefits | Net receivables
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71	33
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,558	1,453	$ 1,297
Postretirement Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	480	496
Postretirement Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133	106
Postretirement Benefits | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	699	629
Postretirement Benefits | Includes Medical Benefit Component Under Section401 H And Excludes Receivables Related To Pending Security Sales [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,312	1,231
Postretirement Benefits | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24	38
Postretirement Benefits | Cash and cash equivalents | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24	38
Postretirement Benefits | Cash and cash equivalents | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Cash and cash equivalents | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	398	386
Postretirement Benefits | U.S. large-capitalization | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	283	279
Postretirement Benefits | U.S. large-capitalization | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | U.S. large-capitalization | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115	107
Postretirement Benefits | U.S. small- and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113	104
Postretirement Benefits | U.S. small- and mid-capitalization | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113	104
Postretirement Benefits | U.S. small- and mid-capitalization | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | U.S. small- and mid-capitalization | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	177	182
Postretirement Benefits | International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60	75
Postretirement Benefits | International | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | International | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	117	107
Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	132	120
Postretirement Benefits | Global | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Global | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Global | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	132	120
Postretirement Benefits | Municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133	106
Postretirement Benefits | Municipal bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133	106
Postretirement Benefits | Municipal bonds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	335	295
Postretirement Benefits | Other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Other | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Postretirement Benefits | Other | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	335	295
Postretirement Benefits | Medical benefit assets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	234	219
Postretirement Benefits | Net receivables
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 12	$ 3

Retirement Benefits (Components

Retirement Benefits (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Non-service Cost or Income Components	$ 136	$ 116	$ 90
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	134	110	88
Interest cost	152	174	187
Expected return on plan assets	(297)	(291)	(276)
Prior service credit	0	(1)	(1)
Actuarial (gain) loss	73	60	25
Defined Benefit Plan, Non-service Cost or Income Components	(72)	(58)	(65)
Net periodic benefit cost (income)	62	52	23
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	23	19	18
Interest cost	33	39	43
Expected return on plan assets	(80)	(80)	(77)
Prior service credit	(4)	(4)	(5)
Actuarial (gain) loss	(6)	(9)	(15)
Defined Benefit Plan, Non-service Cost or Income Components	(57)	(54)	(54)
Net periodic benefit cost (income)	$ (34)	$ (35)	$ (36)

Retirement Benefits (Summary _2

Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 62	$ 52	$ 23
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(34)	(35)	(36)
Union Electric Company | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	29	22	5
Union Electric Company | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(4)	(5)	(6)
Ameren Illinois Company | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	34	32	20
Ameren Illinois Company | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(31)	(31)	(30)
Other | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	(1)	(2)	(2)
Other | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 1	$ 1	$ 0

Retirement Benefits (Schedule O

Retirement Benefits (Schedule Of Expected Payments From Qualified Trust And Company Funds) (Details) $ in Millions	Dec. 31, 2021USD ($)
Pension Benefits | Paid From Qualified Trust
Defined Benefit Plan Disclosure [Line Items]
2022	$ 267
2023	274
2024	279
2025	284
2026	288
2027 – 2031	1,476
Pension Benefits | Paid From Company Funds
Defined Benefit Plan Disclosure [Line Items]
2022	2
2023	2
2024	3
2025	3
2026	3
2027 – 2031	12
Postretirement Benefits | Paid From Qualified Trust
Defined Benefit Plan Disclosure [Line Items]
2022	59
2023	60
2024	61
2025	61
2026	60
2027 – 2031	296
Postretirement Benefits | Paid From Company Funds
Defined Benefit Plan Disclosure [Line Items]
2022	2
2023	2
2024	2
2025	2
2026	2
2027 – 2031	$ 9

Retirement Benefits (Assumpti_2

Retirement Benefits (Assumptions Used To Determine Net Periodic Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate at measurement date	2.75%	3.50%	4.25%
Expected return on plan assets	6.50%	7.00%	7.00%
Increase in future compensation	3.50%	3.50%	3.50%
Cash balance pension plan interest crediting rate	5.00%	5.00%	5.00%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate at measurement date	2.75%	3.50%	4.25%
Expected return on plan assets	6.50%	7.00%	7.00%
Increase in future compensation	3.50%	3.50%	3.50%
Medical cost trend rate (initial)	5.00%	5.00%	5.00%
Medical cost trend rate (ultimate)	5.00%	5.00%	5.00%
Postretirement Health Coverage
Defined Benefit Plan Disclosure [Line Items]
Medical cost trend rate (initial)	2.50%	3.00%
Medical cost trend rate (ultimate)	3.00%

Retirement Benefits (Schedule_2

Retirement Benefits (Schedule Of Matching Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 38	$ 38	$ 35
Union Electric Company
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	21	20	19
Ameren Illinois Company
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	16	17	16
Other
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 1	$ 1	$ 0

Stock-Based Compensation (Narra

Stock-Based Compensation (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	8
Maximum shares available for grants (in shares)	1.8
Settled performance share units and restricted stock units	$ 50	$ 58	$ 83
Compensation cost not yet recognized	$ 35
Expected weighted average recognition period for share-based compensation expense, in months	21 months
Income taxes
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 5	$ 8	$ 15
Performance Share Units | Market Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Share-Based Compensation Arrangement By Share-Based Payment Award, Extended Award Vesting Period	38 months
Award Requisite Service Period	5 years
Percentage of shares issued per share unit, minimum	0.00%
Percentage of shares issued per share unit, maximum	200.00%
Stock Issued During Period Percentage Conversion Of Units, Mid-point	100.00%
Performance Share Units | Performance Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Share-Based Compensation Arrangement By Share-Based Payment Award, Extended Award Vesting Period	38 months
Award Requisite Service Period	5 years
Percentage of shares issued per share unit, minimum	0.00%
Percentage of shares issued per share unit, maximum	200.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	38 months
Award Requisite Service Period	5 years

Stock-Based Compensation (Summa

Stock-Based Compensation (Summary Of Nonvested Shares) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Performance Share Units | Market Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares issued per share unit, minimum	0.00%
Percentage of shares issued per share unit, maximum	200.00%
Fully Vested Undistributed Retirement-eligible units (in shares)	357,575	366,243
Vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share Units, Nonvested at beginning of year (in shares)	464,139
Share Units, Granted (in shares)	266,081
Share Units, Unearned or forfeited (in shares)	(21,143)
Share Units, Undistributed Vested Units (in shares)	(186,792)
Share Units, Vested and distributed (in shares)	(93,499)
Share Units, Performance Adjustment (in shares)	0
Share Units, Nonvested at end of year (in shares)	428,786	464,139
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted-average Fair Value per Unit, Nonvested at beginning of year (in dollars per share)	$ 73.34
Fair value of share units awarded	87.11	$ 82.49	$ 67.42
Weighted-average Fair Value per Unit, Unearned or forfeited (in dollars per share)	80.77
Weighted-average Fair Value per Unit, Vested and undistributed (in dollars per share)	77.91
Weighted-average Fair Value per Unit, Vested and distributed (in dollars per share)	62.88
Weighted-average Fair Value per Unit, Performance Adjustment (in dollars per share)	0
Weighted-average Fair Value per Unit, Nonvested at end of year (in dollars per share)	$ 81.81	$ 73.34
Performance Share Units | Performance Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shares issued per share unit, minimum	0.00%
Percentage of shares issued per share unit, maximum	200.00%
Fully Vested Undistributed Retirement-eligible units (in shares)	22,739	7,607
Vesting period	3 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share Units, Nonvested at beginning of year (in shares)	31,896
Share Units, Granted (in shares)	42,672
Share Units, Unearned or forfeited (in shares)	(2,449)
Share Units, Undistributed Vested Units (in shares)	(15,134)
Share Units, Vested and distributed (in shares)	0
Share Units, Performance Adjustment (in shares)	(13,881)
Share Units, Nonvested at end of year (in shares)	43,104	31,896
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted-average Fair Value per Unit, Nonvested at beginning of year (in dollars per share)	$ 76.66
Fair value of share units awarded	78.11
Weighted-average Fair Value per Unit, Unearned or forfeited (in dollars per share)	77.55
Weighted-average Fair Value per Unit, Vested and undistributed (in dollars per share)	77.27
Weighted-average Fair Value per Unit, Vested and distributed (in dollars per share)	0
Weighted-average Fair Value per Unit, Performance Adjustment (in dollars per share)	77.54
Weighted-average Fair Value per Unit, Nonvested at end of year (in dollars per share)	$ 77.54	$ 76.66
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fully Vested Undistributed Retirement-eligible units (in shares)	164,000	160,034
Vesting period	38 months
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Share Units, Nonvested at beginning of year (in shares)	303,695
Share Units, Granted (in shares)	129,723
Share Units, Unearned or forfeited (in shares)	(10,209)
Share Units, Undistributed Vested Units (in shares)	(87,427)
Share Units, Vested and distributed (in shares)	(87,597)
Share Units, Performance Adjustment (in shares)	0
Share Units, Nonvested at end of year (in shares)	248,185	303,695
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted-average Fair Value per Unit, Nonvested at beginning of year (in dollars per share)	$ 68.52
Fair value of share units awarded	78.17
Weighted-average Fair Value per Unit, Unearned or forfeited (in dollars per share)	74.88
Weighted-average Fair Value per Unit, Vested and undistributed (in dollars per share)	73.13
Weighted-average Fair Value per Unit, Vested and distributed (in dollars per share)	56.38
Weighted-average Fair Value per Unit, Performance Adjustment (in dollars per share)	0
Weighted-average Fair Value per Unit, Nonvested at end of year (in dollars per share)	$ 75.97	$ 68.52

Stock-Based Compensation (Sum_2

Stock-Based Compensation (Summary of Expense) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 22	$ 21	$ 20
Employee service share-based compensation, tax benefit from compensation expense	6	6	5
Share-based Compensation Expense, Net of Tax	16	15	15
Ameren Missouri [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	5	5	4
Ameren Illinois Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	3	3	3
Other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 14	$ 13	$ 13
Performance Share Units | Market Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of share units awarded	$ 87.11	$ 82.49	$ 67.42
Three-year risk-free rate	0.17%	1.62%	2.46%
Ameren’s common stock volatility	28.00%	15.00%	17.00%
Volatility range for peer group, minimum	26.00%	14.00%	15.00%
Volatility range for peer group, maximum	36.00%	28.00%	25.00%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Deferred Tax Liabilities, Net	$ 3,469	$ 3,177
Union Electric Company
Income Taxes [Line Items]
Deferred Tax Liabilities, Net	$ 1,822	$ 1,708
State | Union Electric Company
Income Taxes [Line Items]
State Income Tax Statutory Rate	4.00%
Deferred Tax Liabilities, Net	$ 122
State | Union Electric Company | Maximum
Income Taxes [Line Items]
State Income Tax Statutory Rate	6.25%

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%	21.00%
Amortization of excess deferred income taxes	(8.00%)	(9.00%)	(7.00%)
Amortization of deferred investment tax credit	0.00%	(1.00%)	(1.00%)
Renewable and other tax credits	(3.00%)
State tax	5.00%	5.00%	6.00%
Stock-based compensation	(1.00%)	(1.00%)	(1.00%)
Effective income tax rate	14.00%	15.00%	18.00%
Union Electric Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%	21.00%
Amortization of excess deferred income taxes	(15.00%)	(16.00%)	(11.00%)
Amortization of deferred investment tax credit	(1.00%)	(1.00%)	(1.00%)
Renewable and other tax credits	(7.00%)
State tax	3.00%	3.00%	5.00%
Stock-based compensation	0.00%	0.00%	0.00%
Effective income tax rate	1.00%	7.00%	14.00%
Ameren Illinois Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%	21.00%
Amortization of excess deferred income taxes	(3.00%)	(3.00%)	(4.00%)
Amortization of deferred investment tax credit	0.00%	(1.00%)	0.00%
Renewable and other tax credits	0.00%
State tax	7.00%	7.00%	7.00%
Stock-based compensation	0.00%	0.00%	0.00%
Effective income tax rate	25.00%	24.00%	24.00%

Income Taxes (Schedule Of Compo

Income Taxes (Schedule Of Components Of Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Current Federal taxes	$ 7	$ 2	$ (4)
Current State taxes	(6)	5	19
Deferred Federal Income Tax Expense (Benefit)	170	187	185
Deferred State taxes	86	57	59
Amortization of excess deferred income taxes	(96)	(91)	(72)
Amortization of deferred investment tax credits	(4)	(5)	(5)
Income tax benefit	157	155	182
Union Electric Company
Income Taxes [Line Items]
Current Federal taxes	0	14	65
Current State taxes	0	3	22
Deferred Federal Income Tax Expense (Benefit)	65	82	37
Deferred State taxes	23	15	5
Amortization of excess deferred income taxes	(81)	(75)	(56)
Amortization of deferred investment tax credits	(4)	(5)	(5)
Income tax benefit	3	34	68
Ameren Illinois Company
Income Taxes [Line Items]
Current Federal taxes	(15)	12	19
Current State taxes	(7)	(6)	11
Deferred Federal Income Tax Expense (Benefit)	120	81	66
Deferred State taxes	59	52	29
Amortization of excess deferred income taxes	(14)	(15)	(15)
Amortization of deferred investment tax credits	0	0	0
Income tax benefit	143	124	110
Other
Income Taxes [Line Items]
Current Federal taxes	22	(24)	(88)
Current State taxes	1	8	(14)
Deferred Federal Income Tax Expense (Benefit)	(15)	24	82
Deferred State taxes	4	(10)	25
Amortization of excess deferred income taxes	(1)	(1)	(1)
Amortization of deferred investment tax credits	0	0	0
Income tax benefit	$ 11	$ (3)	$ 4

Income Taxes (Schedule Of Defer

Income Taxes (Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Plant-related	$ 4,129	$ 3,876
Regulatory assets and liabilities, net	(483)	(515)
Deferred employee benefit costs - asset	(88)	(104)
Tax carryforwards	(198)	(97)
Other - liabilities	109	17
Total net accumulated deferred income tax liabilities (assets)	3,469	3,177
Accumulated deferred investment tax credits	30	34
Accumulated deferred income taxes and investment tax credits	3,499	3,211
Union Electric Company
Income Taxes [Line Items]
Plant-related	2,188	2,112
Regulatory assets and liabilities, net	(259)	(285)
Deferred employee benefit costs - asset	(52)	(58)
Tax carryforwards	(68)	(26)
Other - liabilities	13
Other - assets		(35)
Total net accumulated deferred income tax liabilities (assets)	1,822	1,708
Accumulated deferred investment tax credits	30	34
Accumulated deferred income taxes and investment tax credits	1,852	1,742
Ameren Illinois Company
Income Taxes [Line Items]
Plant-related	1,715	1,559
Regulatory assets and liabilities, net	(199)	(207)
Deferred employee benefit costs - liability	17	8
Tax carryforwards	(46)	(6)
Other - liabilities	71	13
Total net accumulated deferred income tax liabilities (assets)	1,558	1,367
Accumulated deferred investment tax credits	0	0
Accumulated deferred income taxes and investment tax credits	1,558	1,367
Other
Income Taxes [Line Items]
Plant-related	226	205
Regulatory assets and liabilities, net	(25)	(23)
Deferred employee benefit costs - asset	(53)	(54)
Tax carryforwards	(84)	(65)
Other - liabilities	25	39
Total net accumulated deferred income tax liabilities (assets)	89	102
Accumulated deferred investment tax credits	0	0
Accumulated deferred income taxes and investment tax credits	$ 89	$ 102

Income Taxes (Schedule Of Net O

Income Taxes (Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Net operating loss carryforwards:
Net operating loss carryforwards:	$ 65	$ 7
Tax credit carryforwards	133	90
Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	34
Tax credit carryforwards	126	83
State
Net operating loss carryforwards:
Net operating loss carryforwards:	31	7
Tax credit carryforwards	7	7
Union Electric Company
Net operating loss carryforwards:
Net operating loss carryforwards:	3	0
Tax credit carryforwards	65	26
Union Electric Company | Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	2
Tax credit carryforwards	65	26
Union Electric Company | State
Net operating loss carryforwards:
Net operating loss carryforwards:	1	0
Tax credit carryforwards	0	0
Ameren Illinois Company
Net operating loss carryforwards:
Net operating loss carryforwards:	42	3
Tax credit carryforwards	4	3
Ameren Illinois Company | Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	17
Tax credit carryforwards	3	3
Ameren Illinois Company | State
Net operating loss carryforwards:
Net operating loss carryforwards:	25	3
Tax credit carryforwards	1	0
Other
Net operating loss carryforwards:
Net operating loss carryforwards:	20	4
Tax credit carryforwards	64	61
Other | Federal
Net operating loss carryforwards:
Net operating loss carryforwards:	15
Tax credit carryforwards	58	54
Other | State
Net operating loss carryforwards:
Net operating loss carryforwards:	5	4
Tax credit carryforwards	$ 6	$ 7

Related Party Transactions (Nar

Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2019
Related Party Transaction [Line Items]
Interconnection agreement, optional termination period	3 years
Ameren Illinois Capacity Supply Agreements with Ameren Missouri | Ameren Illinois Company | 2021 Procurements
Related Party Transaction [Line Items]
Energy Supply Agreements Amount	$ 2
Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Support services agreement, optional termination period	60 days
Ameren Services Support Services Agreement | Ameren Illinois Company
Related Party Transaction [Line Items]
Due from Related Parties	$ 80
Ameren Services Support Services Agreement | Union Electric Company
Related Party Transaction [Line Items]
Due from Related Parties	$ 77
Ameren Missouri Software Licensing with Ameren Illinois | Ameren Illinois Electric Distribution
Related Party Transaction [Line Items]
Revenue from Related Parties		$ 14
Ameren Missouri Software Licensing with Ameren Illinois | Ameren Illinois Gas
Related Party Transaction [Line Items]
Revenue from Related Parties		5
Ameren Missouri Software Licensing with Ameren Illinois | Ameren Illinois Company
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction		24
Capitalized Computer Software, Net		5
Revenue from Related Parties		19
Ameren Missouri Software Licensing with Ameren Illinois | Union Electric Company
Related Party Transaction [Line Items]
Capitalized Computer Software, Gross		$ 24

Related Party Transactions (Sch

Related Party Transactions (Schedule of Related Party Electric Power Supply Agreements) (Details) - Ameren Illinois Company - Ameren Illinois Power Supply Agreements with Ameren Missouri	12 Months Ended
	Dec. 31, 2021MWh$ / MWh
April 2017 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	85,600
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	34
April 2018 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	110,000
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	32
April 2019 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	288,000
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	35
September 2019 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	170,800
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	29
September 2020 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	204,800
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	31
April 2021 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	33,600
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	34
September 2021 Procurement
Schedule of Related Party Electric Power Supply Agreements [Line Items]
Related Party Long Term Contract For Purchase Of Electric Power | MWh	136,000
Related Party Long Term Contract For Purchase Of Electric Power Rate | $ / MWh	37

Related Party Transactions (S_2

Related Party Transactions (Schedule of Affiliate Receivables and Payables) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Union Electric Company
Related Party Transaction [Line Items]
Accounts payable – affiliates	$ 46	$ 46
Accounts Receivable, Related Parties, Current	44	57
Union Electric Company | Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts payable – affiliates	0	0
Union Electric Company | Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	27	9
Ameren Illinois Company
Related Party Transaction [Line Items]
Accounts payable – affiliates	64	51
Accounts Receivable, Related Parties, Current	24	64
Ameren Illinois Company | Income taxes payable to parent
Related Party Transaction [Line Items]
Accounts payable – affiliates	8	6
Ameren Illinois Company | Income taxes receivable from parent
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	$ 18	$ 15

Related Party Transactions (S_3

Related Party Transactions (Schedule of Capital Contributions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Union Electric Company
Related Party Transaction [Line Items]
Capital contribution from parent	$ 207	$ 491	$ 124
Ameren Illinois Company
Related Party Transaction [Line Items]
Capital contribution from parent	$ 262	$ 464	$ 15

Related Party Transactions (Eff

Related Party Transactions (Effects of Related-party Transactions on the Statement of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Union Electric Company | Ameren Missouri Power Supply Agreements with Ameren Illinois
Related Party Transaction [Line Items]
Operating Revenues	$ 16	$ 11	$ 3
Union Electric Company | Ameren Missouri and Ameren Illinois Rent and Facility Services
Related Party Transaction [Line Items]
Operating Revenues	26	26	27
Operating Expenses	1	1	2
Union Electric Company | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI
Related Party Transaction [Line Items]
Operating Revenues	1	3	1
Union Electric Company | Total Operating Revenues
Related Party Transaction [Line Items]
Operating Revenues	42	40	31
Union Electric Company | Ameren Illinois Transmission Services From ATXI
Related Party Transaction [Line Items]
Operating Expenses	4
Union Electric Company | Total Purchased Power
Related Party Transaction [Line Items]
Operating Expenses	4
Union Electric Company | Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Operating Expenses	147	140	135
Union Electric Company | Total Related Party Other Operations and Maintenance
Related Party Transaction [Line Items]
Operating Expenses	148	140	137
Union Electric Company | Money Pool Borrowings (Advances)
Related Party Transaction [Line Items]
Interest (Charges) Income	1	1	1
Ameren Illinois Company | Ameren Missouri and Ameren Illinois Rent and Facility Services
Related Party Transaction [Line Items]
Operating Revenues	1	1	2
Operating Expenses	4	4	5
Ameren Illinois Company | Ameren Missouri and Ameren Illinois miscellaneous support services and services provided to ATXI
Related Party Transaction [Line Items]
Operating Revenues	5	1	2
Ameren Illinois Company | Ameren Missouri Software Licensing with Ameren Illinois
Related Party Transaction [Line Items]
Operating Revenues			19
Ameren Illinois Company | Total Operating Revenues
Related Party Transaction [Line Items]
Operating Revenues	6	2	23
Ameren Illinois Company | Ameren Illinois Power Supply Agreements with Ameren Missouri
Related Party Transaction [Line Items]
Operating Expenses	16	11	3
Ameren Illinois Company | Ameren Illinois Transmission Services From ATXI
Related Party Transaction [Line Items]
Operating Expenses	1	2	2
Ameren Illinois Company | Total Purchased Power
Related Party Transaction [Line Items]
Operating Expenses	17	13	5
Ameren Illinois Company | Ameren Services Support Services Agreement
Related Party Transaction [Line Items]
Operating Expenses	137	133	127
Ameren Illinois Company | Total Related Party Other Operations and Maintenance
Related Party Transaction [Line Items]
Operating Expenses	141	137	132
Ameren Illinois Company | Money Pool Borrowings (Advances)
Related Party Transaction [Line Items]
Interest (Charges) Income	$ 1	$ 1	$ 1

Commitments And Contingencies (

Commitments And Contingencies (Environmental Matters) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)energyCentersscrubbersite	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Asset Retirement Obligation	$ 764	$ 756	$ 691
Coal Fired Electric Generation Equipment
Plant To Be Abandoned, Net	$ 604
Union Electric Company
Number of Energy Center Scrubbers | scrubber	2
Number of Energy Centers Constructing Wastewater Treatment Facilities | energyCenters	3
Number of Energy Centers | energyCenters	4
Number of Energy Centers Closing Surface Impoundments | energyCenters	2
Number of impoundments closing | energyCenters	2
Number of Days to Comply after Final EPA Determination	135 days
Asset Retirement Obligation	$ 760	751	687
Number of Ameren Missouri Natural Gas Energy Centers Subject To IETL | energyCenters	5
Number of Early Energy Center Closures | energyCenters	1
Union Electric Company | Coal Fired Electric Generation Equipment
Plant To Be Abandoned, Net	$ 604
Ameren Illinois Company
Asset Retirement Obligation	4	$ 5	$ 4
Ameren Illinois Company | Coal Fired Electric Generation Equipment
Plant To Be Abandoned, Net	0
Manufactured Gas Plant
Accrual for environmental loss contingencies	$ 71
Manufactured Gas Plant | Ameren Illinois Company
Number of remediation sites | site	44
Accrual for environmental loss contingencies	$ 71
Minimum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	125
Minimum | Union Electric Company
Estimated capital costs to comply with existing and known federal and state air emissions regulations	125
Minimum | Coal Combustion Residuals Estimate | Union Electric Company
Estimated capital costs to comply with existing and known federal and state air emissions regulations	60
Minimum | Manufactured Gas Plant | Ameren Illinois Company
Estimate of possible loss	71
Maximum
Estimated capital costs to comply with existing and known federal and state air emissions regulations	175
Maximum | Union Electric Company
Estimated capital costs to comply with existing and known federal and state air emissions regulations	175
Maximum | Coal Combustion Residuals Estimate | Union Electric Company
Estimated capital costs to comply with existing and known federal and state air emissions regulations	80
Maximum | Manufactured Gas Plant | Ameren Illinois Company
Estimate of possible loss	125
Rush Island Energy Center | Union Electric Company
Rate Base	400
New CCR Rules Estimate
Asset Retirement Obligation	76
New CCR Rules Estimate | Union Electric Company
Asset Retirement Obligation	$ 76

Supplemental Information (Narra

Supplemental Information (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)MWh	Dec. 31, 2020USD ($)MWh	Dec. 31, 2019USD ($)
Supplemental Information [Line Items]
Wind generation expenditures	$ 525	$ 564	$ 0
Deferred Compensation Liability, Classified, Noncurrent	$ 91	90
Union Electric Company
Supplemental Information [Line Items]
Amount of Megawatts | MWh	102
Wind generation expenditures	$ 525	$ 564	$ 0
Union Electric Company | Wind Generation Facility
Supplemental Information [Line Items]
Amount of Megawatts | MWh	300	400
Atchison Renewable Energy Center purchase price	$ 500
High Prairie Renewable Energy Center purchase price		$ 615
Ameren Illinois Company
Supplemental Information [Line Items]
Payables for purchased receivables	$ 27	$ 28

Supplemental Information (Cash

Supplemental Information (Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 8	$ 139
Restricted cash included in “Other current assets”	16	17
Restricted Cash and Cash Equivalents, Noncurrent	127	141
Restricted Cash and Cash Equivalents, Nuclear Decommissioning Trust Fund	4	4
Total cash, cash equivalents, and restricted cash	155	301	$ 176	$ 107
Union Electric Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	136
Restricted cash included in “Other current assets”	4	5
Restricted Cash and Cash Equivalents, Noncurrent	0	0
Restricted Cash and Cash Equivalents, Nuclear Decommissioning Trust Fund	4	4
Total cash, cash equivalents, and restricted cash	8	145	39	8
Ameren Illinois Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	0
Restricted cash included in “Other current assets”	6	6
Restricted Cash and Cash Equivalents, Noncurrent	127	141
Restricted Cash and Cash Equivalents, Nuclear Decommissioning Trust Fund	0	0
Total cash, cash equivalents, and restricted cash	$ 133	$ 147	$ 125	$ 80

Supplemental Information (Allow

Supplemental Information (Allowance for Doubtful Accounts) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning of period	$ 50	$ 17
Bad debt expense	9	48
Net write-offs	(30)	(15)
End of period	29	50
Union Electric Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning of period	16	7
Bad debt expense	5	15
Net write-offs	(8)	(6)
End of period	13	16
Ameren Illinois Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning of period	34	10
Bad debt expense	4	33
Net write-offs	(22)	(9)
End of period	$ 16	$ 34

Supplemental Information (Inven

Supplemental Information (Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Public Utilities, Inventory [Line Items]
Fuel	$ 118	$ 115
Natural gas stored underground	99	57
Materials, supplies, and other	375	349
Total inventories	592	521
Union Electric Company
Public Utilities, Inventory [Line Items]
Fuel	118	115
Natural gas stored underground	9	5
Materials, supplies, and other	292	266
Total inventories	419	386
Ameren Illinois Company
Public Utilities, Inventory [Line Items]
Fuel	0	0
Natural gas stored underground	90	52
Materials, supplies, and other	83	83
Total inventories	$ 173	$ 135

Supplemental Information (Sched

Supplemental Information (Schedule of Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation	$ 764	$ 756	$ 691
Liabilities incurred	18	36
Liabilities settled	(37)	(58)
Accretion	31	30
Change in estimates	(4)	57
Current asset retirement obligations	7	60
Nuclear Plant
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation	574
Union Electric Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation	760	751	687
Liabilities incurred	18	36
Liabilities settled	(36)	(58)
Accretion	31	29
Change in estimates	(4)	57
Current asset retirement obligations	7	60
Ameren Illinois Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset Retirement Obligation	4	5	$ 4
Liabilities incurred	0	0
Liabilities settled	(1)	0
Accretion	0	1
Change in estimates	$ 0	$ 0

Supplemental Information (Sch_2

Supplemental Information (Schedule of Excise Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Line Items]
Excise Tax Expense	$ 275	$ 254	$ 264
Union Electric Company
Accounting Policies [Line Items]
Excise Tax Expense	150	139	147
Ameren Illinois Company
Accounting Policies [Line Items]
Excise Tax Expense	$ 125	$ 115	$ 117

Supplemental Information (All_2

Supplemental Information (Allowance For Funds Used During Construction) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for Funds Used During Construction, Rate [Line Items]
Allowance for equity funds used during construction	$ 43	$ 32	$ 28
Allowance for borrowed funds used during construction	17	16	20
Total allowance for funds used during construction	$ 60	$ 48	$ 48
Union Electric Company
Allowance for Funds Used During Construction, Rate [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	6.00%	5.00%	6.00%
Allowance for equity funds used during construction	$ 26	$ 19	$ 19
Allowance for borrowed funds used during construction	10	10	12
Total allowance for funds used during construction	$ 36	$ 29	$ 31
Ameren Illinois Company
Allowance for Funds Used During Construction, Rate [Line Items]
Public Utilities, Allowance for Funds Used During Construction, Rate	5.00%	5.00%	5.00%
Allowance for equity funds used during construction	$ 17	$ 13	$ 9
Allowance for borrowed funds used during construction	7	6	8
Total allowance for funds used during construction	$ 24	$ 19	$ 17

Supplemental Information (Earni

Supplemental Information (Earnings Per Share) (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share Reconciliation [Abstract]
Weighted-average Common Shares Outstanding – Basic	256,300,000	247,000,000	245,600,000
Assumed settlement of performance share units and restricted stock units	1,300,000	1,200,000	1,400,000
Dilutive effect of forward sale agreements	0	500,000	100,000
Weighted Average Number of Shares Outstanding, Diluted (in shares)	257,600,000	248,700,000	247,100,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)		0	0

Supplemental Information (Suppl

Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	$ 508	$ 446	$ 333
Net realized and unrealized gain – nuclear decommissioning trust fund	163	116	143
Exchange of bond investments for extinguishment of senior unsecured notes	0	0	(17)
Noncash financing activity – Issuance of common stock for stock-based compensation	33	38	54
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	285	229	140
Net realized and unrealized gain – nuclear decommissioning trust fund	163	116	143
Exchange of bond investments for extinguishment of senior unsecured notes	0	0	0
Noncash financing activity – Issuance of common stock for stock-based compensation	0	0	0
Ameren Illinois Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	215	218	163
Net realized and unrealized gain – nuclear decommissioning trust fund	0	0	0
Exchange of bond investments for extinguishment of senior unsecured notes	0	0	(17)
Noncash financing activity – Issuance of common stock for stock-based compensation	0	0	0
Ameren Illinois Company | Senior Unsecured 1993 Series B-1 [Domain] | Unsecured Debt
Supplemental Cash Flow Information [Line Items]
Debt instrument face amount			17
Nuclear Fuel
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	16	0	19
Nuclear Fuel | Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	16	0	19
Nuclear Fuel | Ameren Illinois Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	$ 0	$ 0	$ 0

Segment Information (Schedule O

Segment Information (Schedule Of Segment Reporting Information By Segment) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	4
External revenues	$ 6,394	$ 5,794	$ 5,910
Depreciation and amortization	1,146	1,075	995
Interest income	27	29	33
Interest Charges	383	419	381
Income tax benefit	157	155	182
Net Income (Loss) Available to Common Stockholders, Basic	990	871	828
Capital expenditures	3,479	3,233	2,411
Wind generation expenditures	$ 525	564	0
Reportable Subsegments
Segment Reporting Information [Line Items]
External revenues			5,891
Intersubsegment Eliminations
Segment Reporting Information [Line Items]
Intersegment revenues			19
Union Electric Company
Segment Reporting Information [Line Items]
Number of reportable segments | segment	1
Ameren Illinois Electric Distribution | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues			14
Ameren Illinois Gas | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues			5
Ameren Illinois Company
Segment Reporting Information [Line Items]
Number of reportable segments | segment	3
External revenues	$ 2,895	2,535	2,527
Depreciation and amortization	472	434	406
Interest income	1	3	6
Interest Charges	164	155	147
Income tax benefit	143	124	110
Net Income Available to Common Shareholder	425	379	343
Capital expenditures	1,432	1,447	1,208
Ameren Illinois Company | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Intersegment revenues			19
Operating Segments | Union Electric Company
Segment Reporting Information [Line Items]
External revenues	3,311	3,069	3,212
Depreciation and amortization	632	604	556
Interest income	26	26	26
Interest Charges	137	190	178
Income tax benefit	3	34	68
Net Income Available to Common Shareholder	518	436	426
Capital expenditures	2,015	1,666	1,076
Operating Segments | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	1,635	1,496	1,487
Depreciation and amortization	309	288	273
Interest income	1	2	6
Interest Charges	74	72	71
Income tax benefit	53	42	45
Net Income Available to Common Shareholder	165	143	146
Capital expenditures	579	543	518
Operating Segments | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	957	760	791
Depreciation and amortization	90	81	78
Interest income	0	0	0
Interest Charges	42	41	38
Income tax benefit	39	36	30
Net Income Available to Common Shareholder	108	99	84
Capital expenditures	278	301	318
Operating Segments | Ameren Transmission
Segment Reporting Information [Line Items]
External revenues	491	469	401
Depreciation and amortization	111	98	84
Interest income	0	1	1
Interest Charges	83	78	74
Income tax benefit	82	78	64
Net Income Available to Common Shareholder	230	216	185
Capital expenditures	616	716	528
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
External revenues	1,639	1,498	1,504
Depreciation and amortization	309	288	273
Interest income	1	2	6
Interest Charges	74	72	71
Income tax benefit	53	42	45
Net Income Available to Common Shareholder	165	143	146
Capital expenditures	579	543	518
Operating Segments | Ameren Illinois Company | Ameren Illinois Gas
Segment Reporting Information [Line Items]
External revenues	957	760	797
Depreciation and amortization	90	81	78
Interest income	0	0	0
Interest Charges	42	41	38
Income tax benefit	39	36	30
Net Income Available to Common Shareholder	108	99	84
Capital expenditures	278	301	318
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
External revenues	299	277	226
Depreciation and amortization	73	65	55
Interest income	0	1	0
Interest Charges	48	42	38
Income tax benefit	51	46	35
Net Income Available to Common Shareholder	152	137	113
Capital expenditures	575	603	372
Segment Reconciling Items
Segment Reporting Information [Line Items]
Depreciation and amortization	4	4	4
Interest income	3	4	5
Interest Charges	50	42	25
Income tax benefit	(20)	(35)	(25)
Net Income Available to Common Shareholder	(31)	(23)	(13)
Capital expenditures	4	5	3
Intersegment Elimination
Segment Reporting Information [Line Items]
Intersegment revenues	117	96	98
Depreciation and amortization	0	0	0
Interest income	(3)	(4)	(5)
Interest Charges	(3)	(4)	(5)
Income tax benefit	0	0	0
Capital expenditures	(13)	2	(32)
Intersegment Elimination | Ameren Missouri Software Licensing with Ameren Illinois
Segment Reporting Information [Line Items]
Capital expenditures			24
Intersegment Elimination | Union Electric Company
Segment Reporting Information [Line Items]
Intersegment revenues	42	40	31
Intersegment Elimination | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	4	2	17
Intersegment Elimination | Ameren Illinois Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	6
Intersegment Elimination | Ameren Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	71	54	63
Intersegment Elimination | Ameren Illinois Company
Segment Reporting Information [Line Items]
Intersegment revenues	66	52	62
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Electric Distribution
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Gas
Segment Reporting Information [Line Items]
Intersegment revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Transmission
Segment Reporting Information [Line Items]
Intersegment revenues	$ 66	$ 52	$ 62

Segment Information (Disaggrega

Segment Information (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
External revenues	$ 6,394	$ 5,794	$ 5,910
Revenues from alternative revenue programs	77	36	(70)
Revenue Not from Contract with Customer, Other	68	36	28
Revenues	6,394	5,794	5,910
Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	(16)	(14)	35
Revenue Not from Contract with Customer, Other	56	25	19
Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	77	(20)	(74)
Revenue Not from Contract with Customer, Other	10	8	7
Ameren Illinois Electric Distribution | Ameren Missouri Software Licensing with Ameren Illinois
Disaggregation of Revenue [Line Items]
Revenue from Related Parties			14
Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	5	20	0
Revenue Not from Contract with Customer, Other	2	2	2
Ameren Illinois Gas | Ameren Missouri Software Licensing with Ameren Illinois
Disaggregation of Revenue [Line Items]
Revenue from Related Parties			5
Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	11	50	(31)
Revenue Not from Contract with Customer, Other	0	1	0
Electric
Disaggregation of Revenue [Line Items]
External revenues	5,297	4,911	4,981
Revenues	5,297	4,911	4,981
Electric | Residential
Disaggregation of Revenue [Line Items]
External revenues	2,378	2,240	2,251
Electric | Commercial
Disaggregation of Revenue [Line Items]
External revenues	1,671	1,511	1,654
Electric | Industrial
Disaggregation of Revenue [Line Items]
External revenues	415	385	405
Electric | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	833	775	671
Natural gas
Disaggregation of Revenue [Line Items]
External revenues	1,097	883	929
Revenues	1,097	883	929
Natural gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	736	617	651
Natural gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	206	165	188
Natural gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	39	18	17
Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	116	83	73
Ameren Illinois Company
Disaggregation of Revenue [Line Items]
External revenues	2,895	2,535	2,527
Revenues from alternative revenue programs	91	42	(107)
Revenue Not from Contract with Customer, Other	12	10	9
Revenues	2,895	2,535	2,527
Ameren Illinois Company | Ameren Missouri Software Licensing with Ameren Illinois
Disaggregation of Revenue [Line Items]
Revenue from Related Parties			19
Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,590	1,408	1,418
Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	717	622	651
Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	170	138	140
Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	418	367	318
Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	77	(20)	(74)
Revenue Not from Contract with Customer, Other	10	8	7
Ameren Illinois Company | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	5	20	0
Revenue Not from Contract with Customer, Other	2	2	2
Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues from alternative revenue programs	9	42	(33)
Revenue Not from Contract with Customer, Other	0	0	0
Ameren Illinois Company | Electric
Disaggregation of Revenue [Line Items]
External revenues	1,938	1,775	1,730
Ameren Illinois Company | Natural gas
Disaggregation of Revenue [Line Items]
External revenues	957	760	797
Operating Segments | Union Electric Company
Disaggregation of Revenue [Line Items]
External revenues	3,311	3,069	3,212
Revenues	3,353	3,109	3,243
Operating Segments | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
External revenues	1,635	1,496	1,487
Revenues	1,639	1,498	1,504
Operating Segments | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
External revenues	957	760	791
Revenues	957	760	797
Operating Segments | Ameren Transmission
Disaggregation of Revenue [Line Items]
External revenues	491	469	401
Revenues	562	523	464
Operating Segments | Electric | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	3,212	2,984	3,109
Operating Segments | Electric | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	1,445	1,373	1,403
Operating Segments | Electric | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	1,126	1,025	1,157
Operating Segments | Electric | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	280	261	278
Operating Segments | Electric | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	361	325	271
Operating Segments | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	1,639	1,498	1,504
Operating Segments | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	933	867	848
Operating Segments | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	545	486	497
Operating Segments | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	135	124	127
Operating Segments | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	26	21	32
Operating Segments | Electric | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Operating Segments | Electric | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	562	523	464
Operating Segments | Electric | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Electric | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	562	523	464
Operating Segments | Natural gas | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenues	141	125	134
Operating Segments | Natural gas | Union Electric Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	79	76	81
Operating Segments | Natural gas | Union Electric Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	34	29	34
Operating Segments | Natural gas | Union Electric Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	4	4	4
Operating Segments | Natural gas | Union Electric Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	24	16	15
Operating Segments | Natural gas | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Operating Segments | Natural gas | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	957	760	797
Operating Segments | Natural gas | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	657	541	570
Operating Segments | Natural gas | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	172	136	154
Operating Segments | Natural gas | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	35	14	13
Operating Segments | Natural gas | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	93	69	60
Operating Segments | Natural gas | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Natural gas | Ameren Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Operating Segments | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
External revenues	1,639	1,498	1,504
Operating Segments | Ameren Illinois Company | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
External revenues	957	760	797
Operating Segments | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
External revenues	299	277	226
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenues	1,639	1,498	1,504
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Residential
Disaggregation of Revenue [Line Items]
External revenues	933	867	848
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Commercial
Disaggregation of Revenue [Line Items]
External revenues	545	486	497
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Industrial
Disaggregation of Revenue [Line Items]
External revenues	135	124	127
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Electric Distribution | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	26	21	32
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenues	365	329	288
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Operating Segments | Ameren Illinois Company | Electric | Ameren Illinois Transmission | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	365	329	288
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenues	957	760	797
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	657	541	570
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	172	136	154
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	35	14	13
Operating Segments | Ameren Illinois Company | Natural gas | Ameren Illinois Gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	93	69	60
Intersegment Elimination
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(117)	(96)	(98)
Revenues	(117)	(96)	(98)
Intersegment Elimination | Union Electric Company
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(42)	(40)	(31)
Intersegment Elimination | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(4)	(2)	(17)
Intersegment Elimination | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	(6)
Intersegment Elimination | Ameren Transmission
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(71)	(54)	(63)
Intersegment Elimination | Electric
Disaggregation of Revenue [Line Items]
Revenues	(116)	(94)	(96)
Intersegment Elimination | Electric | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Electric | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Electric | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Electric | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(116)	(94)	(96)
Intersegment Elimination | Natural gas
Disaggregation of Revenue [Line Items]
Revenues	(1)	(2)	(2)
Intersegment Elimination | Natural gas | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Natural gas | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Natural gas | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Natural gas | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(1)	(2)	(2)
Intersegment Elimination | Ameren Illinois Company
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(66)	(52)	(62)
Revenues	(66)	(52)	(62)
Intersegment Elimination | Ameren Illinois Company | Residential
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Commercial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Industrial
Disaggregation of Revenue [Line Items]
External revenues	0	0	0
Intersegment Elimination | Ameren Illinois Company | Other
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	(66)	(52)	(62)
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Electric Distribution
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Gas
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	0	0	0
Intersegment Elimination | Ameren Illinois Company | Ameren Illinois Transmission
Disaggregation of Revenue [Line Items]
Revenue Not from Contract with Customer	$ (66)	$ (52)	$ (62)

Schedule I - Condensed Financ_2

Schedule I - Condensed Financial Information Of Parent (Statement of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Operating revenues	$ 6,394	$ 5,794	$ 5,910
Operating expenses	5,061	4,494	4,643
Operating loss	1,333	1,300	1,267
Interest income from affiliates	2	4	8
Total other expense, net	202	151	130
Interest Charges	(383)	(419)	(381)
Income tax benefit	157	155	182
Comprehensive Income from Continuing Operations
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	14	16	5
Comprehensive Income Attributable to Ameren Common Shareholders	1,004	887	833
Other Comprehensive Income (Loss), Taxes:
Pension and other postretirement benefit plan activity, tax (benefit)	4	5	1
Parent Company
Condensed Financial Statements, Captions [Line Items]
Operating revenues	0	0	0
Operating expenses	13	12	15
Operating loss	(13)	(12)	(15)
Equity in earnings of subsidiaries	1,039	908	850
Interest income from affiliates	3	4	5
Total other expense, net	0	(8)	(2)
Interest Charges	(64)	(57)	(39)
Income tax benefit	25	36	29
Net Income Available to Common Shareholder	990	871	828
Comprehensive Income from Continuing Operations
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	14	16	5
Comprehensive Income Attributable to Ameren Common Shareholders	1,004	887	833
Other Comprehensive Income (Loss), Taxes:
Pension and other postretirement benefit plan activity, tax (benefit)	$ 4	$ 5	$ 1

Schedule I - Condensed Financ_3

Schedule I - Condensed Financial Information Of Parent (Balance Sheet) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets:
Cash and cash equivalents	$ 8	$ 139
Miscellaneous accounts and notes receivable	85	65
Other current assets	229	135
Total current assets	1,968	1,653
Other assets	891	789
Total assets	35,735	32,030
Liabilities and Shareholders' Equity:
Short-term debt	545	490
Other current liabilities	445	489
Total current liabilities	2,826	2,180
Long-term debt	12,562	11,078
Other deferred credits and liabilities	414	503
Commitments and Contingencies (Note 5)
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 257.7 and 253.3, respectively	3	3
Other paid-in capital, principally premium on common stock	6,502	6,179
Retained earnings	3,182	2,757
Accumulated other comprehensive income (loss)	13	(1)
Total shareholders’ equity	9,829	9,080	$ 8,201
TOTAL LIABILITIES AND EQUITY	$ 35,735	$ 32,030
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	257,700,000	253,300,000	246,200,000	244,500,000
Parent Company
Assets:
Cash and cash equivalents	$ 0	$ 0
Advances to money pool	108	16
Accounts receivable – affiliates	30	12
Miscellaneous accounts and notes receivable	11	15
Other current assets	4	4
Total current assets	153	47
Investments in subsidiaries	12,281	10,872
Note receivable – ATXI	35	75
Accumulated deferred income taxes, net	65	42
Other assets	184	167
Total assets	12,718	11,203
Liabilities and Shareholders' Equity:
Short-term debt	277	490
Taxes accrued	7	0
Accounts payable – affiliates	53	41
Other current liabilities	38	34
Total current liabilities	375	565
Long-term debt	2,533	1,588
Pension and other postretirement benefits	24	27
Other deferred credits and liabilities	86	85
Total liabilities	3,018	2,265
Commitments and Contingencies (Note 5)
Common stock, $.01 par value, 400.0 shares authorized – shares outstanding of 257.7 and 253.3, respectively	3	3
Other paid-in capital, principally premium on common stock	6,502	6,179
Retained earnings	3,182	2,757
Accumulated other comprehensive income (loss)	13	(1)
Total shareholders’ equity	9,700	8,938
TOTAL LIABILITIES AND EQUITY	$ 12,718	$ 11,203
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	257,700,000	253,300,000

Schedule I - Condensed Financ_4

Schedule I - Condensed Financial Information Of Parent (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Condensed Financial Statements, Captions [Line Items]
Net cash flows provided by operating activities	$ 1,661	$ 1,727	$ 2,170
Cash Flows From Investing Activities:
Other	8	11	3
Net cash flows used in investing activities	(3,528)	(3,329)	(2,435)
Cash flows from financing activities:
Dividends on common stock	(565)	(494)	(472)
Short-term debt, net	55	50	(157)
Maturities of long-term debt	(8)	(442)	(580)
Issuances of long-term debt	1,997	2,183	1,527
Issuances of common stock	308	476	68
Employee payroll taxes related to stock-based compensation	(17)	(20)	(29)
Debt issuance costs	(18)	(20)	(17)
Net cash flows provided by (used in) financing activities	1,721	1,727	334
Cash, cash equivalents, and restricted cash at beginning of year	301	176	107
Cash, cash equivalents, and restricted cash at end of year	155	301	176
Noncash Investing and Financing Items [Abstract]
Noncash financing activity – Issuance of common stock for stock-based compensation	33	38	54
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net cash flows provided by operating activities	79	147	491
Cash Flows From Investing Activities:
Money pool advances, net	(92)		(26)
Money pool advances, net		86
Notes receivable – ATXI	40	0	0
Investments in subsidiaries	(489)	(956)	(142)
Other	7	8	5
Net cash flows used in investing activities	(534)	(862)	(163)
Cash flows from financing activities:
Dividends on common stock	(565)	(494)	(472)
Short-term debt, net	(213)	337	(317)
Money pool borrowings, net	0	(24)	(22)
Maturities of long-term debt	0	(350)	0
Issuances of long-term debt	949	798	450
Issuances of common stock	308	476	68
Employee payroll taxes related to stock-based compensation	(17)	(20)	(29)
Debt issuance costs	(7)	(7)	(4)
Net cash flows provided by (used in) financing activities	455	716	(326)
Net change in cash, cash equivalents, and restricted cash	0	1	2
Cash, cash equivalents, and restricted cash at beginning of year	4	3	1
Cash, cash equivalents, and restricted cash at end of year	4	4	3
Cash dividends received from consolidated subsidiaries	123	105	445
Noncash Investing and Financing Items [Abstract]
Noncash financing activity – Issuance of common stock for stock-based compensation	$ 33	$ 38	$ 54

Schedule I - Condensed Financ_5

Schedule I - Condensed Financial Information Of Parent Cash and Cash Equivalents (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	$ 8	$ 139
Restricted cash included in “Other current assets”	16	17
Total cash, cash equivalents, and restricted cash	155	301	$ 176	$ 107
Parent Company
Schedule of Cash and Cash Equivalents Including Restricted Cash [Line Items]
Cash and cash equivalents	0	0
Restricted cash included in “Other current assets”	4	4
Total cash, cash equivalents, and restricted cash	$ 4	$ 4	$ 3	$ 1

Schedule I - Condensed Financ_6

Schedule I - Condensed Financial Information Of Parent Other Income (Expense), Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Nonoperating Income (Expense) [Line Items]
Non-service cost components of net periodic benefit income	$ 136	$ 116	$ 90
Donations	(9)	(25)	(12)
Total other expense, net	202	151	130
Parent Company
Other Nonoperating Income (Expense) [Line Items]
Non-service cost components of net periodic benefit income	1	1	2
Donations	0	(8)	(3)
Other expense, net	(1)	(1)	(1)
Total other expense, net	$ 0	$ (8)	$ (2)

Schedule II - Valuation And Q_2

Schedule II - Valuation And Qualifying Accounts (Details) - Allowance For Doubtful Accounts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 50	$ 17	$ 18
Charged to Costs and Expenses	9	42	26
Charged to Other Accounts	0	6	4
Deductions	30	15	31
Balance at End of Period	29	50	17
Union Electric Company
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	16	7	7
Charged to Costs and Expenses	5	15	9
Charged to Other Accounts	0	0	0
Deductions	8	6	9
Balance at End of Period	13	16	7
Ameren Illinois Company
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	34	10	11
Charged to Costs and Expenses	4	27	17
Charged to Other Accounts	0	6	4
Deductions	22	9	22
Balance at End of Period	$ 16	$ 34	$ 10