ACCUMULATED OTHER COMPREHENSIVE LOSS Reclassification Out of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 149	$ 86
Unrealized gains (losses) on investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	2	(12)
Reclassification from AOCI, Current Period, Tax	(1)	4
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1	(8)
Pension and other postretirement benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	154	149
Reclassification from AOCI, Current Period, Tax	(28)	(47)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	126	102
Derivative instruments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	27	(7)
Reclassification from AOCI, Current Period, Tax	(5)	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 22	$ (8)