Property and Plant, Net (Schedule of Capitalized Software) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Capitalized software costs
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 78	$ 71	$ 58
Gross carrying value	901	734
Accumulated amortization	(584)	(514)
Union Electric Company | Capitalized software costs
Finite-Lived Intangible Assets [Line Items]
Amortization expense	30	24	20
Gross carrying value	303	223
Accumulated amortization	(153)	(125)
Ameren Illinois Company | Capitalized software costs
Finite-Lived Intangible Assets [Line Items]
Amortization expense	45	44	$ 36
Gross carrying value	377	297
Accumulated amortization	$ (221)	$ (183)
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years