EMPLOYEE RETIREMENT PLANS - Unrealized Loss Included in Accumulated Other Comprehensive (Loss) Income before Income Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Qualified
Amounts in accumulated other comprehensive income (loss) before income taxes
Net loss	$ 442	$ 519
Net transition obligation	0	1
Net prior service cost	3	3
Total	445	523
Non-Qualified
Amounts in accumulated other comprehensive income (loss) before income taxes
Net loss	59	54
Net transition obligation	0	0
Net prior service cost	0	0
Total	$ 59	$ 54