SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (8)	$ (9)
Net current period other comprehensive loss	4	1
Ending balance	(4)	(8)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(127)	474
Amounts reclassified from other comprehensive income:	(1)	15
Accumulated Defined Benefit Plans Adjustment, Net Transition Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	130	(468)
Amounts reclassified from other comprehensive income:	(4)	(19)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:		(6)
Amounts reclassified from other comprehensive income:	6	5
Pension Plan | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(25)	(25)
Net current period other comprehensive loss	4	0
Ending balance	(21)	(25)
Pension Plan | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(104)	333
Amounts reclassified from other comprehensive income:	3	13
Other comprehensive income before reclassifications, tax	41	229
Amounts reclassified from other comprehensive income, tax	2	9
Pension Plan | Accumulated Defined Benefit Plans Adjustment, Net Transition Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	107	(327)
Amounts reclassified from other comprehensive income:	2	(9)
Other comprehensive income before reclassifications, tax	41	225
Amounts reclassified from other comprehensive income, tax	1	6
Pension Plan | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:		(6)
Amounts reclassified from other comprehensive income:	(4)	(4)
Other comprehensive income before reclassifications, tax		4
Amounts reclassified from other comprehensive income, tax	2	3
PBOP Plans | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	17	16
Net current period other comprehensive loss	0	1
Ending balance	17	17
PBOP Plans | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(23)	141
Amounts reclassified from other comprehensive income:	(4)	2
Other comprehensive income before reclassifications, tax	9	97
Amounts reclassified from other comprehensive income, tax	1	2
PBOP Plans | Accumulated Defined Benefit Plans Adjustment, Net Transition Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	23	(141)
Amounts reclassified from other comprehensive income:	(6)	(10)
Other comprehensive income before reclassifications, tax	9	97
Amounts reclassified from other comprehensive income, tax	3	8
PBOP Plans | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:		0
Amounts reclassified from other comprehensive income:	10	9
Other comprehensive income before reclassifications, tax		0
Amounts reclassified from other comprehensive income, tax	$ 4	$ 6