Exploration and Evaluation Assets (Tables)

12 Months Ended

Dec. 31, 2019

Exploration For And Evaluation Of Mineral Resources [Abstract]

Schedule of Exploration and Evaluation Assets

($ millions)	2019		2018
Exploration and evaluation assets at cost	1,848.1		2,325.0
Accumulated amortization	(1,602.6	)	(1,852.4	)
Net carrying amount	245.5		472.6
Reconciliation of movements during the year
Cost, beginning of year	2,325.0		2,305.1
Accumulated amortization, beginning of year	(1,852.4	)	(1,670.2	)
Net carrying amount, beginning of year	472.6		634.9
Net carrying amount, beginning of year	472.6		634.9
Acquisitions through business combinations, net	7.3		10.2
Additions	384.9		673.3
Dispositions	(101.9	)	(7.5	)
Transfers to property, plant and equipment	(380.6	)	(705.9	)
Amortization	(129.1	)	(157.2	)
Foreign exchange	(7.7	)	24.8
Net carrying amount, end of year	245.5		472.6

($ millions)	2019		2018
Development and production assets	23,038.6		26,635.3
Corporate assets	117.2		114.6
Property, plant and equipment at cost	23,155.8		26,749.9
Accumulated depletion, depreciation and impairment	(15,314.2	)	(16,319.7	)
Net carrying amount	7,841.6		10,430.2
Reconciliation of movements during the year
Development and production assets
Cost, beginning of year	26,635.3		25,881.1
Accumulated depletion and impairment, beginning of year	(16,262.2	)	(11,877.1	)
Net carrying amount, beginning of year	10,373.1		14,004.0
Net carrying amount, beginning of year	10,373.1		14,004.0
Acquisitions through business combinations, net	8.7		12.2
Additions	1,075.7		1,083.6
Dispositions, net	(1,230.9	)	(523.8	)
Transfers from exploration and evaluation assets	380.6		705.9
Reclassified as assets held for sale	(195.0	)	—
Depletion	(1,087.4	)	(1,412.4	)
Impairment	(1,466.4	)	(3,704.8	)
Foreign exchange	(70.8	)	208.4
Net carrying amount, end of year	7,787.6		10,373.1
Cost, end of year	23,038.6		26,635.3
Accumulated depletion and impairment, end of year	(15,251.0	)	(16,262.2	)
Net carrying amount, end of year	7,787.6		10,373.1
Corporate assets
Cost, beginning of year	114.6		106.4
Accumulated depreciation, beginning of year	(57.5	)	(48.0	)
Net carrying amount, beginning of year	57.1		58.4
Net carrying amount, beginning of year	57.1		58.4
Additions	2.9		7.7
Depreciation	(5.9	)	(9.2	)
Foreign exchange	(0.1	)	0.2
Net carrying amount, end of year	54.0		57.1
Cost, end of year	117.2		114.6
Accumulated depreciation, end of year	(63.2	)	(57.5	)
Net carrying amount, end of year	54.0		57.1