Consolidated Statement Of Income (Loss) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Revenues:
Total operating revenues	$ 5,794	$ 5,910	$ 6,291
Operating Expenses:
Fuel	490	535	769
Purchased power	513	556	581
Natural gas purchased for resale	272	331	374
Other operations and maintenance	1,661	1,745	1,772
Depreciation and amortization	1,075	995	955
Taxes other than income taxes	483	481	483
Total operating expenses	4,494	4,643	4,934
Operating Income	1,300	1,267	1,357
Other Income, Net	151	130	102
Interest Charges	419	381	401
Income Before Income Taxes	1,032	1,016	1,058
Income Taxes	155	182	237
Net Income	877	834	821
Less: Net Income Attributable to Noncontrolling Interests	6	6	6
Net Income Attributable to Ameren Common Shareholders	871	828	815
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	16	5	(4)
Comprehensive Income	893	839	817
Less: Comprehensive Income Attributable to Noncontrolling Interests	6	6	6
Comprehensive Income Attributable to Ameren Common Shareholders	$ 887	$ 833	$ 811
Earnings per Common Share – Basic:
Earnings per Common Share – Basic	$ 3.53	$ 3.37	$ 3.34
Earnings per Common Share – Diluted:
Earnings per Common Share – Diluted	$ 3.50	$ 3.35	$ 3.32
Weighted-average Common Shares Outstanding – Basic	247.0	245.6	243.8
Weighted-average Common Shares Outstanding – Diluted	248.7	247.1	245.8
Union Electric Company
Operating Revenues:
Total operating revenues	$ 3,109	$ 3,243	$ 3,589
Operating Expenses:
Fuel	490	535	769
Purchased power	171	193	164
Natural gas purchased for resale	43	53	56
Other operations and maintenance	886	960	972
Depreciation and amortization	604	556	550
Taxes other than income taxes	328	329	329
Total operating expenses	2,522	2,626	2,840
Operating Income	587	617	749
Other Income, Net	76	58	56
Interest Charges	190	178	200
Income Before Income Taxes	473	497	605
Income Taxes	34	68	124
Net Income	439	429	481
Preferred Stock Dividends	3	3	3
Net Income Available to Common Shareholder	436	426	478
Ameren Illinois Company
Operating Revenues:
Total operating revenues	2,535	2,527	2,576
Operating Expenses:
Purchased power	355	368	429
Natural gas purchased for resale	229	278	318
Other operations and maintenance	775	782	799
Depreciation and amortization	434	406	374
Taxes other than income taxes	140	143	144
Total operating expenses	1,933	1,977	2,064
Operating Income	602	550	512
Other Income, Net	59	53	42
Interest Charges	155	147	149
Income Before Income Taxes	506	456	405
Income Taxes	124	110	98
Net Income	382	346	307
Preferred Stock Dividends	3	3	3
Net Income Available to Common Shareholder	379	343	304
Electric
Operating Revenues:
Total operating revenues	4,911	4,981	5,339
Electric | Union Electric Company
Operating Revenues:
Total operating revenues	2,984	3,109	3,451
Electric | Ameren Illinois Company
Operating Revenues:
Total operating revenues	1,775	1,730	1,761
Natural gas
Operating Revenues:
Total operating revenues	883	929	952
Natural gas | Union Electric Company
Operating Revenues:
Total operating revenues	125	134	138
Natural gas | Ameren Illinois Company
Operating Revenues:
Total operating revenues	$ 760	$ 797	$ 815