INVESTMENTS - Transitional Real Estate Loans by Key Credit Quality Indicators (Details) - Transitional real estate loans $ in Millions	Mar. 31, 2021 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
2021	$ 23
2020	508
2019	2,109
2018	1,897
2017	470
Total Financing Receivable	5,007
Loan to Value Ratio, Zero to Fifty-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	53
2019	548
2018	396
2017	77
Total Financing Receivable	1,074
Loan to Value Ratio, Sixty to Sixty-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	170
2019	830
2018	766
2017	208
Total Financing Receivable	1,974
Loan to Value Ratio, Seventy to Seventy-nine Point Nine-nine Percent
Financing Receivable, Credit Quality Indicator [Line Items]
2021	23
2020	259
2019	731
2018	735
2017	185
Total Financing Receivable	1,933
Loan-to-Value Ratio Eighty Percent and Above
Financing Receivable, Credit Quality Indicator [Line Items]
2021	0
2020	26
2019	0
2018	0
2017	0
Total Financing Receivable	$ 26