2010 Corporate Reorganization (Narrative) (Details)	0 Months Ended
	Oct. 02, 2010
Ameren Illinois Merger [Member]
Business Acquisition [Line Items]
Equity capital structure, minimum	30.00%
Central Illinois Public Service Company [Member]
Business Acquisition [Line Items]
Dissenters rights exercised, preferred stock, shares	8,337
Illinois Power Company [Member]
Business Acquisition [Line Items]
Preferred stock, conversion ratio	2
Dissenters rights exercised, preferred stock, shares	423