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