Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Details) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 1,699	[1]	$ 1,601
Total Unrealized Gains		1,033	[1]	1,190
Total Unrealized Losses		(21)	[1]	(13)
Total Fair Value		2,711	[1]	2,778
Amount primarily related to deferred taxes on appreciation of investment value		294		324
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		21		17
Total Unrealized Gains		0		0
Total Unrealized Losses		0		0
Total Fair Value		21		17
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost				5
Total Unrealized Gains				28
Total Unrealized Losses				0
Total Fair Value				33
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,168		1,059
Total Unrealized Gains		70		75
Total Unrealized Losses		(5)		(4)
Total Fair Value		1,233		1,130
Nuclear Decommissioning Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]			1,596
Total Unrealized Gains	[1]			1,162
Total Unrealized Losses	[1]			(13)
Total Fair Value	[1]			2,745
Global equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		510		520
Total Unrealized Gains		963		1,087
Total Unrealized Losses		(16)		(9)
Total Fair Value		$ 1,457		$ 1,598

[1] Represents amounts before deducting $294 million and $324 million at September 30, 2015 and December 31, 2014, respectively, primarily related to deferred taxes on appreciation of investment value.