Equipment (Details) - Equipment - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Cost
Opening balance	$ 39	$ 38
Closing balance	39	38
Accumulated depreciation
Opening balance	(20)	(15)
Depreciation	(3)	(3)
Closing balance	(23)	(18)
Net book value	$ 16	$ 20	$ 19	$ 23

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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