Fair Value Measurements (Schedule Of Unrealized Gains Losses Related To Available-For-Sale Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amount primarily related to deferred taxes on appreciation of investment value		$ 333	$ 314
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		9	36
Total Unrealized Gains		0	0
Total Unrealized Losses		0	0
Total Fair Value		9	36
Global equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		584	508
Total Unrealized Gains		1,157	1,034
Total Unrealized Losses		(3)	(9)
Total Fair Value		1,738	1,533
Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,156	1,165
Total Unrealized Gains		48	58
Total Unrealized Losses		(12)	(8)
Total Fair Value		1,192	1,215
Securities (Assets) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1],[2]	1,749
Total Unrealized Gains	[1],[2]	1,205
Total Unrealized Losses	[1],[2]	(15)
Total Fair Value	[1],[2]	$ 2,939
Nuclear Decommissioning Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]		1,709
Total Unrealized Gains	[1]		1,092
Total Unrealized Losses	[1]		(17)
Total Fair Value	[1]		$ 2,784

[1] Represents amount before deducting $313 million, primarily related to deferred taxes on appreciation of investment value.

[2] Represents amounts before deducting $333 million and $314 million at December 31, 2016 and 2015, respectively, primarily related to deferred taxes on appreciation of investment value.