INVESTMENTS - Transitional Real Estate Loans by Key Credit Quality Indicators (Details) - Transitional real estate loans $ in Millions	Sep. 30, 2021 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 1,435
2020	403
2019	1,713
2018	1,219
2017	441
Total Financing Receivable	5,211
Loan to Value Ratio, Zero to Fifty-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2021	449
2020	55
2019	439
2018	353
2017	77
Total Financing Receivable	1,373
Loan to Value Ratio, Sixty to Sixty-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2021	417
2020	136
2019	831
2018	543
2017	182
Total Financing Receivable	2,109
Loan to Value Ratio, Seventy to Seventy-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2021	569
2020	184
2019	443
2018	323
2017	182
Total Financing Receivable	1,701
Loan-to-Value Ratio Eighty Percent and Above
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	28
2019	0
2018	0
2017	0
Total Financing Receivable	$ 28