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