Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Details) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2016		Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]	$ 1,744		$ 1,709
Total Unrealized Gains	[1]	1,205		1,092
Total Unrealized Losses	[1]	(6)		(17)
Total Fair Value	[1]	2,943		2,784
Amount primarily related to deferred taxes on appreciation of investment value		346	[2]	314	[3]
Short-term investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1		36
Total Unrealized Gains		0		0
Total Unrealized Losses		0		0
Total Fair Value		1		36
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,164		1,165
Total Unrealized Gains		89		58
Total Unrealized Losses		(3)		(8)
Total Fair Value		1,250		1,215
Global equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		579		508
Total Unrealized Gains		1,116		1,034
Total Unrealized Losses		(3)		(9)
Total Fair Value		$ 1,692		$ 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.

[2] Represents amount before deducting $346 million, primarily related to deferred taxes on appreciation of investment value.

[3] Represents amount before deducting $314 million, primarily related to deferred taxes on appreciation of investment value.