RETIREMENT BENEFITS AND ASSETS HELD IN TRUST (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Document Fiscal Year Focus			2020
Defined Contribution Plan, Cost	$ 1,000,000	$ 1,000,000	$ 4,000,000	$ 3,000,000
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer			4,000,000
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer			3,000,000
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer			5,000,000
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	$ 5,000,000		$ 5,000,000