SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 10,594	$ 19,061	$ 12,903	$ 19,472
Net current period other comprehensive gain (loss)	0	1	0	(4)
Ending balance	8,991	19,696	8,991	19,696
Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Net current period other comprehensive gain (loss)	0	1	0	(4)
Other Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Net current period other comprehensive gain (loss)	0	0	0	0
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4)	(13)	(4)	(8)
Ending balance	(4)	(12)	(4)	(12)
Accumulated Other Comprehensive Income (Loss) | Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(21)	(30)	(21)	(25)
Ending balance	(21)	(29)	(21)	(29)
Accumulated Other Comprehensive Income (Loss) | Other Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	17	17	17	17
Ending balance	17	17	17	17
Amortization of prior service cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	1	2	4	5
Amortization of prior service cost | Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	(1)	(1)	(3)	(3)
Amount attributable to tax	0	0	1	1
Amortization of prior service cost | Other Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	2	3	7	8
Amount attributable to tax	1	1	3	3
Amortization of net actuarial loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	1	0	1	0
Amortization of net actuarial loss | Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	1	1	2	3
Amount attributable to tax	0	0	0	1
Amortization of net actuarial loss | Other Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	0	(1)	(1)	(3)
Amount attributable to tax	0	0	1	1
Regulatory account transfer
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	(2)	(1)	(5)	(4)
Regulatory account transfer | Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	0	1	1	1
Amount attributable to tax	0	0	1	0
Regulatory account transfer | Other Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income	(2)	(2)	(6)	(5)
Amount attributable to tax	$ 1	$ 1	$ 2	2
Reclassification of stranded income tax to retained earnings
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income				(5)
Reclassification of stranded income tax to retained earnings | Pension Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income				(5)
Reclassification of stranded income tax to retained earnings | Other Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from other comprehensive income				$ 0