Consolidated Statement of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Income from Continuing Operations	$ 371	$ 345	$ 626	$ 554
Other Comprehensive Income from Continuing Operations, Net of Taxes
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	(1)	0	1	4
Comprehensive Income from Continuing Operations	370	345	627	558
Less: Comprehensive Income from Continuing Operations Attributable to Noncontrolling Interests	2	2	5	5
Comprehensive Income from Continuing Operations Attributable to Ameren Common Shareholders	368	343	622	553
Comprehensive Income from Discontinued Operations Attributable to Ameren Common Shareholders	0	0	0	52
Comprehensive Income Attributable to Ameren Common Shareholders	$ 368	$ 343	$ 622	$ 605