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, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Nuclear Decommissioning Trust Fund Investments [Line Items]
Sales and maturities of securities - nuclear decommissioning trust fund	$ 391	$ 196	$ 384
Gross realized gains	7	7	6
Gross realized losses	2	5	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	$ 391	$ 196	$ 384