Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Accounts receivable - trade allowance for doubtful accounts	$ 25	$ 19
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	400,000,000	400,000,000
Common stock, shares outstanding (in shares)	243,600,000	242,600,000
Union Electric Company
Accounts receivable - trade allowance for doubtful accounts	$ 9	$ 7
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares outstanding (in shares)	102,100,000	102,100,000
Ameren Illinois Company
Accounts receivable - trade allowance for doubtful accounts	$ 16	$ 12
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	45,000,000	45,000,000
Common stock, shares outstanding (in shares)	25,500,000	25,500,000