FAIR VALUE MEASUREMENT: (Tables)

6 Months Ended

Jun. 30, 2020

FAIR VALUE MEASUREMENT:

Schedule of carrying amount and estimated fair values of the Company's financial instruments

	At June 30, 2020				At December 31, 2019
	Carrying Value		Fair Value		Carrying Value		Fair Value
Liabilities:
Long-term debt level 1		6,192.1		7,798.3		6,190.6		7,675.3
Long-term debt level 2		350.5		381.8		750.2		776.1
Total long-term debt	$	6,542.6	$	8,180.1	$	6,940.8	$	8,451.4

Schedule of fair values of assets and liabilities measured at fair value on a recurring basis

Fair values of assets and liabilities measured at fair value on a recurring basis were calculated as follows as of June 30, 2020 and December 31, 2019 (in millions):

	Fair Value at Measurement Date Using:
					Significant
	Fair Value		Quoted prices in		other		Significant
	as of		active markets for		observable		unobservable
	June 30,		identical assets		inputs		inputs
Description	2020		(Level 1)		(Level 2)		(Level 3)
Assets:
Short term investment:
—Trading securities	$	30.1	$	30.1	$	—	$	—
—Available-for-sale debt securities:
Corporate bonds		—		—		—		—
Asset backed securities		0.3		—		0.3		—
Mortgage backed securities		0.3		—		0.3		—
Accounts receivable:
—Embedded derivatives—Not classified as hedges:
Provisionally priced sales:
Copper		309.0		309.0		—		—
Molybdenum		132.9		132.9		—		—
Total	$	472.6	$	472.0	$	0.6	$	—

	Fair Value at Measurement Date Using:
					Significant
	Fair Value		Quoted prices in		other		Significant
	as of		active markets for		observable		unobservable
	December 31,		identical assets		inputs		inputs
Description	2019		(Level 1)		(Level 2)		(Level 3)
Assets:
Short term investment:
—Trading securities	$	80.0	$	80.0	$	—	$	—
—Available-for-sale debt securities:
Corporate bonds		—		—		—		—
Asset backed securities		0.4		—		0.4		—
Mortgage backed securities		0.3		—		0.3		—
Accounts receivable:
—Embedded derivatives-Not classified as hedges:
Provisionally priced sales:
Copper		326.5		326.5		—		—
Molybdenum		126.8		126.8		—		—
Total	$	534.0	$	533.3	$	0.7	$	—