Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts Receivable, Allowance for Credit Loss, Current	$ 44	$ 17
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000.0	400,000,000.0
Common Stock, Shares, Outstanding	247,200,000	246,200,000
Union Electric Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 14	$ 7
Common stock, par value (in dollars per share)	$ 5,000,000	$ 5,000,000
Common stock, shares authorized (in shares)	150,000,000.0	150,000,000.0
Common Stock, Shares, Outstanding	102,100,000	102,100,000
Ameren Illinois Company
Accounts Receivable, Allowance for Credit Loss, Current	$ 30	$ 10
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	45,000,000.0	45,000,000.0
Common Stock, Shares, Outstanding	25,500,000	25,500,000