ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (8,088)		$ (8,571)	$ (8,591)
Total Equity, Beginning	27,971	$ 28,334	26,961	27,009		$ 27,229
Other comprehensive income (loss) before reclassifications	334	222
Amounts reclassified from accumulated other comprehensive income	149	86
Total other comprehensive income	483	308
Other Comprehensive Income (Loss), Tax	14	59
Unrealized gains (losses) on investments
Total Equity, Beginning	(8)	60	17		$ 43
Other comprehensive income (loss) before reclassifications	(26)	25
Amounts reclassified from accumulated other comprehensive income	1	(8)
Total other comprehensive income	(25)	17
Other Comprehensive Income (Loss), Tax	(6)	8
Cumulative Translation Adjustments
Total Equity, Beginning	(1,105)	(2,142)	(1,481)		(2,381)
Other comprehensive income (loss) before reclassifications	376	239
Amounts reclassified from accumulated other comprehensive income	0	0
Total other comprehensive income	376	239
Other Comprehensive Income (Loss), Tax	(5)	18
Pension and other postretirement benefit plans
Total Equity, Beginning	(6,872)	(7,287)	(6,998)		(7,389)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	126	102
Total other comprehensive income	126	102
Other Comprehensive Income (Loss), Tax	28	47
Derivative instruments
Total Equity, Beginning	(103)	(145)	(109)		(95)
Other comprehensive income (loss) before reclassifications	(16)	(42)
Amounts reclassified from accumulated other comprehensive income	22	(8)
Total other comprehensive income	6	(50)
Other Comprehensive Income (Loss), Tax	(3)	(14)
Accumulated Other Comprehensive Loss
Total Equity, Beginning	(8,088)	(9,514)	(8,571)	$ (8,591)	$ (9,822)	$ (9,822)
Total other comprehensive income	$ 483	$ 308
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax			20
Total Equity, Beginning			$ 0