Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,617		$ 1,569
Total Unrealized Gains	1,208		1,178
Total Unrealized Losses	(4)		(8)
Total Fair Value	2,821		2,739
Amount primarily related to deferred taxes on appreciation of investment value	322		313
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19		38
Total Unrealized Gains	0		0
Total Unrealized Losses	0		0
Total Fair Value	19		38
U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	266		246
Total Unrealized Gains	874		811
Total Unrealized Losses	0		0
Total Fair Value	1,140		1,057
Non-U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	253		215
Total Unrealized Gains	207		242
Total Unrealized Losses	(1)		0
Total Fair Value	459		457
U.S. Government And Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	847		870
Total Unrealized Gains	60		51
Total Unrealized Losses	(2)		(5)
Total Fair Value	905		916
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	52		24
Total Unrealized Gains	3		2
Total Unrealized Losses	0		(1)
Total Fair Value	55		25
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9		13
Total Unrealized Gains	62		71
Total Unrealized Losses	0		0
Total Fair Value	71		84
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	171		163
Total Unrealized Gains	2		1
Total Unrealized Losses	(1)		(2)
Total Fair Value	172		162
Nuclear Decommissioning Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,608	[1]	1,556	[1]
Total Unrealized Gains	1,146	[1]	1,107	[1]
Total Unrealized Losses	(4)	[1]	(8)	[1]
Total Fair Value	$ 2,750	[1]	$ 2,655	[1]

[1] Represents amounts before deducting $322 million and $313 million at June 30, 2014 and December 31, 2013, respectively, primarily related to deferred taxes on appreciation of investment value.