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Equity (Share-based Payments to Employees, Non-marketable Options, Movement) (Details)
Pure in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
2012 Plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Balance as at Start of Period 3 11
Granted during the year 0 0
Expired during the period (3) (8)
Forfeited during the year 0 0
Balance as at End of Period 0 3
2014 Plan [Member]    
Disclosure of terms and conditions of share-based payment arrangement [Line Items]    
Balance as at Start of Period 14 12
Granted during the year 7 4
Expired during the period 0 0
Forfeited during the year (1) (2)
Balance as at End of Period 20 14