Consolidated Balance Sheet - AIC (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounts receivable - trade, allowance for doubtful accounts	$ 29	$ 50
Common Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	257,700,000	253,300,000
Ameren Illinois Company
Accounts receivable - trade, allowance for doubtful accounts	$ 16	$ 34
Common Stock, No Par Value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized	45,000,000.0	45,000,000.0
Common Stock, Shares, Outstanding	25,500,000	25,500,000