Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,629		$ 1,569
Total Unrealized Gains	1,159		1,178
Total Unrealized Losses	(7)		(8)
Total Fair Value	2,781		2,739
Amount primarily related to deferred taxes on appreciation of investment value	337		313
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	31		38
Total Unrealized Gains	0		0
Total Unrealized Losses	0		0
Total Fair Value	31		38
U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	269		246
Total Unrealized Gains	830		811
Total Unrealized Losses	0		0
Total Fair Value	1,099		1,057
Non-U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	251		215
Total Unrealized Gains	191		242
Total Unrealized Losses	(2)		0
Total Fair Value	440		457
U.S. Government And Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	856		870
Total Unrealized Gains	54		51
Total Unrealized Losses	(3)		(5)
Total Fair Value	907		916
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38		24
Total Unrealized Gains	3		2
Total Unrealized Losses	(1)		(1)
Total Fair Value	40		25
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13		13
Total Unrealized Gains	80		71
Total Unrealized Losses	0		0
Total Fair Value	93		84
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	171		163
Total Unrealized Gains	1		1
Total Unrealized Losses	(1)		(2)
Total Fair Value	171		162
Nuclear Decommissioning Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,616	[1]	1,556	[1]
Total Unrealized Gains	1,079	[1]	1,107	[1]
Total Unrealized Losses	(7)	[1]	(8)	[1]
Total Fair Value	$ 2,688	[1]	$ 2,655	[1]

[1] Represents amounts before deducting $337 million and $313 million at March 31, 2014 and December 31, 2013, respectively, primarily related to deferred taxes on appreciation of investment value.