INVESTMENTS - Transitional Real Estate Loans by Key Credit Quality Indicators (Details) - Transitional real estate loans $ in Millions	Sep. 30, 2020 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 530
2019	2,143
2018	2,058
2017	822
2016	34
Prior	57
Total Financing Receivable	5,644
Loan to Value Ratio, Zero to Fifty-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2020	48
2019	529
2018	382
2017	158
2016	20
Prior	57
Total Financing Receivable	1,194
Loan to Value Ratio, Sixty to Sixty-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2020	324
2019	811
2018	825
2017	440
2016	0
Prior	0
Total Financing Receivable	2,400
Loan to Value Ratio, Seventy to Seventy-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2020	132
2019	767
2018	851
2017	224
2016	14
Prior	0
Total Financing Receivable	1,988
Loan-to-Value Ratio Eighty Percent and Above
Financing Receivable, Credit Quality Indicator [Line Items]
2020	26
2019	36
2018	0
2017	0
2016	0
Prior	0
Total Financing Receivable	$ 62