Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,509		$ 1,498
Total Unrealized Gains	998		905
Total Unrealized Losses	(1)		(2)
Total Fair Value	2,506	[1]	2,401	[1]
Amount primarily related to deferred taxes on appreciation of investment value	273		240
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25		21
Total Fair Value	25	[1]	21	[1]
U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	289		331
Total Unrealized Gains	705		618
Total Unrealized Losses	0		0
Total Fair Value	994	[1]	949	[1]
Non-U.S. Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	199		199
Total Unrealized Gains	196		181
Total Unrealized Losses	(1)		(1)
Total Fair Value	394	[1]	379	[1]
U.S. Government And Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	762		723
Total Unrealized Gains	89		97
Total Unrealized Losses	0		0
Total Fair Value	851	[1]	820	[1]
Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61		56
Total Unrealized Gains	4		4
Total Unrealized Losses	0		(1)
Total Fair Value	65	[1]	59	[1]
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	173		168
Total Unrealized Gains	4		5
Total Unrealized Losses	0		0
Total Fair Value	$ 177	[1]	$ 173	[1]

[1] Excludes $273 million and $240 million at March 31, 2013 and December 31, 2012, respectively, primarily related to deferred taxes on appreciation of investment value.