Nuclear Decommissioning Trust Fund Investments (Proceeds From The Sale Of Investments And Related Gross Realized Gains And Losses In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Nuclear Decommissioning Trust Fund Investments [Line Items]
Sales and maturities of securities - nuclear decommissioning trust fund	$ 377	$ 349	$ 391
Gross realized gains	7	8	7
Gross realized losses	$ 4	2	2
Minimum | Nuclear Decommissioning Trust Fund
Nuclear Decommissioning Trust Fund Investments [Line Items]
Trust fund investments, target allocation percentage	60.00%
Maximum | Nuclear Decommissioning Trust Fund
Nuclear Decommissioning Trust Fund Investments [Line Items]
Trust fund investments, target allocation percentage	70.00%
Union Electric Company
Nuclear Decommissioning Trust Fund Investments [Line Items]
Sales and maturities of securities - nuclear decommissioning trust fund	$ 377	$ 349	$ 391