SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (4)	$ (8)
Net current period other comprehensive loss	(1)	4
Ending balance	(5)	(4)
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:	288	(127)
Amounts reclassified from other comprehensive income:	0	(1)
Accumulated Defined Benefit Plans Adjustment, Net Transition Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income before reclassifications:	(289)	130
Amounts reclassified from other comprehensive income:	(6)	(4)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income:	6	6
Pension Plan | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(21)	(25)
Net current period other comprehensive loss	(1)	4
Ending balance	(22)	(21)
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:	61	(104)
Amounts reclassified from other comprehensive income:	2	3
Other comprehensive income before reclassifications, tax	24	41
Amounts reclassified from other comprehensive income, tax	1	2
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:	(62)	107
Amounts reclassified from other comprehensive income:	2	2
Other comprehensive income before reclassifications, tax	24	41
Amounts reclassified from other comprehensive income, tax	1	1
Pension Plan | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income:	(4)	(4)
Amounts reclassified from other comprehensive income, tax	2	2
PBOP Plans | Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	17	17
Net current period other comprehensive loss	0	0
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:	227	(23)
Amounts reclassified from other comprehensive income:	(2)	(4)
Other comprehensive income before reclassifications, tax	88	9
Amounts reclassified from other comprehensive income, tax	1	1
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:	(227)	23
Amounts reclassified from other comprehensive income:	(8)	(6)
Other comprehensive income before reclassifications, tax	88	9
Amounts reclassified from other comprehensive income, tax	3	3
PBOP Plans | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income:	10	10
Amounts reclassified from other comprehensive income, tax	$ 4	$ 4