Summary Of Significant Accounting Policies (Schedule Of Material And Supplies) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Line Items]
Fuel	[1]	$ 173	$ 134
Gas stored underground		97	127
Other materials and supplies		268	263
Total materials and supplies		538	524
Union Electric Company
Accounting Policies [Line Items]
Fuel	[1]	173	134
Gas stored underground		10	16
Other materials and supplies		204	197
Total materials and supplies		387	347
Ameren Illinois Company
Accounting Policies [Line Items]
Fuel	[1]	0	0
Gas stored underground		87	111
Other materials and supplies		64	66
Total materials and supplies		$ 151	$ 177

[1] (a)Consists of coal, oil, and propane.