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, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	$ 218.4	$ 185.2
Service cost	43.6	47.4	$ 40.6
Interest cost	8.3	5.8	4.3
Benefit payments	9.0	7.2
Actuarial loss (gain)	9.9	(12.8)
Projected benefit obligation at end of year	271.2	218.4	185.2
Change in plan assets:
Fair value of plan assets at beginning of year	143.4	121.7
Actual return on plan assets	29.0	(6.2)
Benefits paid	9.0	7.2
Employer contributions	34.0	35.1
Fair value of plan assets at end of year	197.4	143.4	121.7
Reconciliation of funded status:
Fair value of plan assets at end of year	197.4	143.4	121.7	$ 197.4	$ 143.4
Less benefit obligation at end of year	271.2	218.4	185.2	271.2	218.4
Funded status at end of year				(73.8)	(75.0)
Post Retirement Medical Plan [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	19.3	21.6
Service cost	1.0	1.1	1.2
Interest cost	0.7	0.7	0.8
Benefit payments	1.3	0.7
Actuarial loss (gain)	(2.2)	(3.4)
Projected benefit obligation at end of year	17.5	19.3	21.6
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	1.3	0.7
Employer contributions	1.3	0.7
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 obligation at end of year	$ 17.5	$ 19.3	$ 21.6	17.5	19.3
Funded status at end of year				$ (17.5)	$ (19.3)