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