Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Details) - USD ($) $ in Millions		6 Months Ended	12 Months Ended
		Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]	$ 1,758	$ 1,709
Total Unrealized Gains	[1]	1,149	1,092
Total Unrealized Losses	[1]	(18)	(17)
Total Fair Value	[1]	2,889	2,784
Amount primarily related to deferred taxes on appreciation of investment value		343	314
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		11	36
Total Unrealized Gains		0	0
Total Unrealized Losses		0	0
Total Fair Value		11	36
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,126	1,165
Total Unrealized Gains		98	58
Total Unrealized Losses		(3)	(8)
Total Fair Value		1,221	1,215
Global equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		621	508
Total Unrealized Gains		1,051	1,034
Total Unrealized Losses		(15)	(9)
Total Fair Value		$ 1,657	$ 1,533

[1] Represents amounts before deducting $343 million and $314 million at June 30, 2016 and December 31, 2015, respectively, primarily related to deferred taxes on appreciation of investment value.