INCOME TAXES: (Tables)

12 Months Ended

Dec. 31, 2017

INCOME TAXES:

Components of the provision for income taxes

(in millions)	2017			2016			2015
U.S. federal and state:
Current	$	—		$	—		$	—
Deferred		686.2			(109.4	)		(143.0	)
Uncertain tax positions		16.2			20.3			80.0
		702.4			(89.1	)		(63.0	)
Foreign (Peru and Mexico):
Current		951.7			625.0			620.4
Deferred		(60.7	)		(34.8	)		(92.5	)
		891.0			590.2			527.9
Total provision for income taxes	$	1,593.4		$	501.1		$	464.9

Schedule of source of income

(in millions)	2017			2016			2015
Earnings by location:
U.S.	$	(1.5	)	$	(1.9	)	$	(2.1	)
Foreign
Peru		284.6			(85.7	)		213.2
Mexico		2,019.6			1,343.6			978.1
		2,304.2			1,257.9			1,191.3
Earnings before taxes on income	$	2,302.7		$	1,256.0		$	1,189.2

Reconciliation of the statutory income tax rate to the effective tax rate

        The reconciliation of the statutory income tax rate to the effective tax rate for the three years ended December 31, 2017, is as follows (in percentage points):

	2017			2016			2015
Expected tax at U.S. statutory rate		35.0	%		35.0	%		35.0	%
Foreign tax at other than statutory rate, net of foreign tax credit benefit(1)		0.6			2.0			3.6
Percentage depletion		(2.9	)		(2.7	)		(5.9	)
Other permanent differences		5.2			—			0.7
Valuation allowance on US deferred tax assets, foreign tax credits and US tax effect on Peruvian deferred		26.9			—			—
Decrease in US deferred tax asset due to tax rate changes		4.8			—			—
US one time transition tax on accumulated foreign earnings		2.4			—			—
Increase (decrease) in unrecognized tax benefits for uncertain tax positions		0.7			0.2			6.7
Repatriated foreign earnings		(2.0	)		3.6			—
Amounts (over) / under provided in prior years		(0.1	)		(0.5	)		(2.2	)
Other		(1.4	)		2.3			1.2
Effective income tax rate		69.2	%		39.9	%		39.1	%

(1)           Foreign tax at other than statutory rates, net of foreign tax credit benefit, also includes the effects of permanent differences in Peru and Mexico, that are determined at the local statutory rate.

Schedule of deferred tax assets and liabilities

	At December 31,
(in millions)	2017			2016
Assets:
Inventories	$	47.0		$	27.9
Capitalized exploration expenses		9.5			17.5
U.S. foreign tax credit carryforward, net of FIN 48 liability		280.2			284.2
U.S. tax effect of Peruvian deferred tax liability		174.1			162.6
Property, plant and equipment		—			1.2
Reserves		152.6			108.9
Mexican tax on consolidated dividends		14.5			13.6
Prepaids		—			11.1
Valuation allowance on US deferred tax assets, foreign tax credits and US tax effect on Peruvian deferred		(619.6	)		—
Other		9.4			29.7
Total deferred tax assets		67.7			656.7
Liabilities:
Property, plant and equipment		(130.3	)		—
Deferred charges		(16.9	)		(35.4	)
Unremitted foreign earnings		—			(45.7	)
Other		(1.2	)		(10.9	)
Total deferred tax liabilities		(148.4	)		(92.0	)
Total net deferred tax (liabilities) / assets	$	(80.7	)	$	564.7

Summary of expiry of foreign tax credits

Year	Amount
2022		20.3
2023		69.2
2024		102.0
2025		189.5
2026		104.8
Total	$	485.8

Summary of income tax rate and dividend tax rate due to change in enacted tax law

Year	Income Tax Rate			Dividend Tax Rate
2015 - 2016		28.0	%		6.8	%
2017 and later		29.5	%		5	%

Schedule of reconciliation of amount of unrecognized tax benefits

        The total amount of unrecognized tax benefits in 2017, 2016 and 2015, was as follows (in millions):

	2017			2016			2015
Unrecognized tax benefits, opening balance	$	304.0		$	400.0		$	319.4
Gross increases—tax positions in prior period		(89.5	)		3.9			36.3
Gross increases—current-period tax positions		—			23.3			44.3
Decreases related to settlements with taxing authorities		—			(123.2	)		—
		(89.5	)		(96.0	)		80.6
Unrecognized tax benefits, ending balance	$	214.5		$	304.0		$	400.0

Summary of tax years remaining open to examination and adjustment in major tax jurisdictions

Peru:	2012 and all subsequent years
U.S.:	2012 and all subsequent years
Mexico:	2012 and all subsequent years