Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,614		$ 1,569
Total Unrealized Gains	1,139		1,178
Total Unrealized Losses	(12)		(8)
Total Fair Value	2,741		2,739
Amount primarily related to deferred taxes on appreciation of investment value	306		313
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16		38
Total Unrealized Gains	0		0
Total Unrealized Losses	0		0
Total Fair Value	16		38
U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	269		246
Total Unrealized Gains	863		811
Total Unrealized Losses	(2)		0
Total Fair Value	1,130		1,057
Non-U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	256		215
Total Unrealized Gains	183		242
Total Unrealized Losses	(6)		0
Total Fair Value	433		457
U.S. Government And Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	855		870
Total Unrealized Gains	57		51
Total Unrealized Losses	(3)		(5)
Total Fair Value	909		916
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	50		24
Total Unrealized Gains	4		2
Total Unrealized Losses	0		(1)
Total Fair Value	54		25
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5		13
Total Unrealized Gains	31		71
Total Unrealized Losses	0		0
Total Fair Value	36		84
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	163		163
Total Unrealized Gains	1		1
Total Unrealized Losses	(1)		(2)
Total Fair Value	163		162
Nuclear Decommissioning Trusts [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,609	[1]	1,556	[1]
Total Unrealized Gains	1,108	[1]	1,107	[1]
Total Unrealized Losses	(12)	[1]	(8)	[1]
Total Fair Value	$ 2,705	[1]	$ 2,655	[1]

[1] Represents amounts before deducting $306 million and $313 million at September 30, 2014 and December 31, 2013, respectively, primarily related to deferred taxes on appreciation of investment value.