Consolidated Statement of Comprehensive Income (Loss) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Income from Continuing Operations	$ 345	$ 296	$ 554	$ 546
Other Comprehensive Income from Continuing Operations, Net of Taxes
Pension and other postretirement benefit plan activity, net of income taxes (benefit)	0	0	4	3
Comprehensive Income from Continuing Operations	345	296	558	549
Less: Comprehensive Income from Continuing Operations Attributable to Noncontrolling Interests	2	2	5	5
Comprehensive Income from Continuing Operations Attributable to Ameren Common Stockholders	343	294	553	544
Income (Loss) from Discontinued Operations, Net of Taxes	0	(1)	52	(3)
Other Comprehensive Income from Discontinued Operations, Net of Taxes	0	0	0	0
Comprehensive Income (Loss) from Discontinued Operations Attributable to Ameren Common Stockholders	0	(1)	52	(3)
Comprehensive Income	$ 343	$ 293	$ 605	$ 541