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DECOMISSIONING PROVISION (Tables)
 12 Months Ended
Dec. 31, 2019
Other Provisions, Contingent Liabilities And Contingent Assets [Abstract]  
Disclosure of decommissioning provisions
($ millions)
2019

2018

Balance at January 1
573

551

Unwinding of discount rate
14

12

Change in rates
191

—

Acquisition (Note 6)
74

—

Additions
28

18

Change in cost estimates and other
(13
)
(8
)
Total
867

573

Less current portion (included in accrued liabilities)
(3
)
(4
)
Balance at December 31
864

569