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, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,858	$ 1,799
Total Unrealized Gains	1,444	1,514
Total Unrealized Losses	(20)	(10)
Total Fair Value	3,282	3,303
Amount primarily related to deferred taxes on appreciation of investment value	440	440
Short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28	23
Total Unrealized Gains	0	0
Total Unrealized Losses	0	0
Total Fair Value	28	23
Global equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	475	524
Total Unrealized Gains	1,405	1,463
Total Unrealized Losses	(1)	(2)
Total Fair Value	1,879	1,985
Fixed-income securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,355	1,252
Total Unrealized Gains	39	51
Total Unrealized Losses	(19)	(8)
Total Fair Value	$ 1,375	$ 1,295