Consolidated Statement of Income (Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension and other postretirement benefit plan activity, tax expense (benefit)		$ (5)	$ 3	$ 3
Ameren Illinois Company
Pension and other postretirement benefit plan activity, tax expense (benefit)	$ (1)	$ (1)	$ (2)	$ (2)