SIGNIFICANT ACCOUNTING POLICIES - New Accounting Pronouncements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity	$ 14,399	$ 15,088	$ 18,798		$ 11,565	$ 13,254	$ 13,781	$ 12,281	$ 12,359	$ 19,395
Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity	$ 1,634	$ 2,580	$ 7,870		2,145	$ 3,191	$ 4,455	$ 4,188	$ 5,039	$ 8,860	$ 6,070
Cumulative effect of period of adoption, adjusted balance
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity					(32)
Cumulative effect of period of adoption, adjusted balance | Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity					$ (32)
Accounting Standards Update 2016-13 | Cumulative effect of period of adoption, adjusted balance | Retained Earnings
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Stockholders' equity				$ (40)