LEGAL PROCEEDINGS - Securities and RICO Class Actions and Related Matters (Details) $ in Millions, $ in Millions				1 Months Ended	4 Months Ended	9 Months Ended	12 Months Ended
	Aug. 04, 2020 CAD ($)	Dec. 16, 2019 USD ($)	Dec. 07, 2017 insurance_policy_period	Oct. 31, 2015 case	Sep. 16, 2016 action	Sep. 30, 2020 USD ($) group case action	Dec. 31, 2015 case	Sep. 13, 2019 action	Sep. 10, 2019 action	Feb. 15, 2019 entity
Canada
Loss Contingencies [Line Items]
Number of suits filed | case							6
Canada | Violation of Canadian Provincial Securities Legislation
Loss Contingencies [Line Items]
Number of suits filed but not yet served | action						2
Number of entities, exercised opt-out right, pursuing action | entity										1
Settled Litigation | Canada | Violation of Canadian Provincial Securities Legislation
Loss Contingencies [Line Items]
Settlement, agreed to pay | $	$ 94
US Securities Litigation | New Jersey
Loss Contingencies [Line Items]
Number of groups of investors filing action | group						37
Number of claims dismissed | case						7
Number of groups of investors filing action, remain pending | group						30
US Securities Litigation | New Jersey | Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Number of suits filed | case				4
US Securities Litigation | Settled Litigation | New Jersey
Loss Contingencies [Line Items]
Settlement, agreed to pay | $		$ 1,210				$ 1,010
RICO Class Actions | New Jersey | Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Number of suits filed | action					3
Derivative Lawsuits
Loss Contingencies [Line Items]
Number of alleged stockholders, filed lawsuits | action								2	2
Insurance Coverage Lawsuit
Loss Contingencies [Line Items]
Number of distinct insurance policy periods | insurance_policy_period			2