EMPLOYEE BENEFIT PLANS (Changes in Benefit Obligations, Fair Value of Plan Assets, and Funded Status of Plan) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	$ 271.2	$ 218.4
Service cost	59.0	43.6	$ 47.4
Interest cost	6.9	8.3	5.8
Plan amendments	0.0	0.0
Benefit payments	(18.0)	(9.0)
Actuarial loss (gain)	10.2	9.9
Projected benefit obligation at end of year	329.3	271.2	218.4
Change in plan assets:
Fair value of plan assets at beginning of year	197.4	143.4
Actual return on plan assets	28.6	29.0
Benefits paid	(18.0)	(9.0)
Employer contributions	47.8	34.0
Fair value of plan assets at end of year	255.8	197.4	143.4
Reconciliation of funded status:
Fair value of plan assets at end of year	255.8	197.4	143.4	$ 255.8	$ 197.4
Less benefit obligations at end of year	271.2	271.2	218.4	329.3	271.2
Funded status at end of year				(73.5)	(73.8)
Post Retirement Medical Plan [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	17.5	19.3
Service cost	1.0	1.0	1.1
Interest cost	0.4	0.7	0.7
Plan amendments	1.8	0.0
Benefit payments	(0.6)	(1.3)
Actuarial loss (gain)	1.9	(2.2)
Projected benefit obligation at end of year	22.0	17.5	19.3
Change in plan assets:
Fair value of plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Benefits paid	(0.6)	(1.3)
Employer contributions	0.6	1.3
Fair value of plan assets at end of year	0.0	0.0	0.0
Reconciliation of funded status:
Fair value of plan assets at end of year	0.0	0.0	0.0	0.0	0.0
Less benefit obligations at end of year	$ 17.5	$ 17.5	$ 19.3	22.0	17.5
Funded status at end of year				$ (22.0)	$ (17.5)