Fair Value Measurements (Schedule Of Unrealized Gains (Losses) Related To Available-For-Sale Investments) (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	[1]	$ 1,741	$ 1,709
Total Unrealized Gains	[1]	1,119	1,092
Total Unrealized Losses	[1]	(13)	(17)
Total Fair Value	[1]	2,847	2,784
Amount primarily related to deferred taxes on appreciation of investment value		331	314
Money Market Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		25	36
Total Unrealized Gains		0	0
Total Unrealized Losses		0	0
Total Fair Value		25	36
Other Fixed-Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,113	1,165
Total Unrealized Gains		81	58
Total Unrealized Losses		(4)	(8)
Total Fair Value		1,190	1,215
Global equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		603	508
Total Unrealized Gains		1,038	1,034
Total Unrealized Losses		(9)	(9)
Total Fair Value		$ 1,632	$ 1,533

[1] Represents amounts before deducting $331 million and $314 million at March 31, 2016 and December 31, 2015, respectively, primarily related to deferred taxes on appreciation of investment value.