PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Actual Returns on Assets Held by Our Pension Trusts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	$ 226	$ 368	$ 808
Direct investments
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	175	258	568
Derivatives
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	$ 51	$ 110	$ 240