Consolidated Statement of Income (Loss) and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating Revenues:
Total operating revenues	$ 1,879	$ 1,566
Operating Expenses:
Fuel	176	65
Purchased power	177	191
Natural gas purchased for resale	293	165
Other operations and maintenance	461	420
Depreciation and amortization	299	281
Taxes other than income taxes	142	128
Total operating expenses	1,548	1,250
Operating Income	331	316
Other Income, Net	60	46
Interest Charges	104	100
Income Before Income Taxes	287	262
Income Taxes	34	27
Net Income	253	235
Less: Net Income Attributable to Noncontrolling Interests	1	2
Net Income Attributable to Ameren Common Shareholders	252	233
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	1	1
Comprehensive Income	254	236
Less: Comprehensive Income Attributable to Noncontrolling Interests	1	2
Comprehensive Income Attributable to Ameren Common Shareholders	$ 253	$ 234
Earnings Per Share, Basic and Diluted [Abstract]
Earnings per Common Share - Basic (in dollars per share)	$ 0.98	$ 0.92
Earnings per Common Share - Diluted (in dollars per share)	$ 0.97	$ 0.91
Weighted Average Common Shares Outstanding - Basic (in shares)	257.9	254.4
Weighted Average Number of Shares Outstanding - Diluted (in shares)	259.0	255.9
Electricity
Operating Revenues:
Total operating revenues	$ 1,318	$ 1,156
Natural gas
Operating Revenues:
Total operating revenues	561	410
Union Electric Company
Operating Revenues:
Total operating revenues	818	704
Operating Expenses:
Fuel	176	65
Purchased power	50	88
Natural gas purchased for resale	46	31
Other operations and maintenance	232	225
Depreciation and amortization	164	156
Taxes other than income taxes	85	77
Total operating expenses	753	642
Operating Income	65	62
Other Income, Net	23	23
Interest Charges	39	39
Income Before Income Taxes	49	46
Income Taxes	(2)	(2)
Net Income	51	48
Preferred Stock Dividends	1	1
Net Income (Loss) Attributable to Parent	50	47
Union Electric Company | Electricity
Operating Revenues:
Total operating revenues	738	641
Union Electric Company | Natural gas
Operating Revenues:
Total operating revenues	80	63
Ameren Illinois Company
Operating Revenues:
Total operating revenues	1,024	823
Operating Expenses:
Purchased power	131	106
Natural gas purchased for resale	247	134
Other operations and maintenance	223	194
Depreciation and amortization	124	115
Taxes other than income taxes	53	46
Total operating expenses	778	595
Operating Income	246	228
Other Income, Net	24	14
Interest Charges	42	42
Income Before Income Taxes	228	200
Income Taxes	59	50
Net Income	169	150
Preferred Stock Dividends	0	1
Net Income (Loss) Attributable to Parent	169	149
Ameren Illinois Company | Electricity
Operating Revenues:
Total operating revenues	543	476
Ameren Illinois Company | Natural gas
Operating Revenues:
Total operating revenues	$ 481	$ 347