Consolidated Statement of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 104	$ 107
Other Comprehensive Loss, Net of Taxes
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	0	(2)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	104	105
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	2	2
Comprehensive Income Attributable to Ameren Common Shareholders	$ 102	$ 103