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Equity (Share-based Payments to Employees, Non-marketable Options, Movement) (Details) - Non-marketable options [Member]
Pure in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Balance as at start of year 30 18
Granted during the year   19
Expired during the year (2) (3)
Forfeited during the year   (3)
Exercised during the year (1) (1)
Balance as at end of year 27 30