SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - INVESTMENT BORROWINGS (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) subsidiary	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Number of insurance subsidiaries that are members of the FHLB | subsidiary	3
Investment borrowings	$ 1,639.5	$ 1,715.8
Interest expense on FHLB borrowings	33.5	$ 9.8	$ 21.2
Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal home loan bank stock	75.2
Investment borrowings	1,639.5
Federal home loan bank advances, collateral pledged	2,200.0
Fixed rate FHLB borrowings pre-payable	81.8
Aggregate fee to prepay all fixed rate FHLB borrowings	1.0
Borrowings due March 2023 at 2.160% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 20.8
Interest rate	2.16%
Borrowings due July 2023 at 4.490% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.49%
Borrowings due July 2023 at 4.490% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.49%
Borrowings due July 2023 at 4.490% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.49%
Borrowings due April 2024 at 4.262% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.262%
Borrowings due May 2024 at 4.919% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.919%
Borrowings due May 2024 at 4.764% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 22.0
Interest rate	4.764%
Borrowings due July 2024 at 4.058% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.058%
Borrowings due July 2024 at 1.990% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 15.5
Interest rate	1.99%
Borrowings due July 2024 at 4.782% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 34.5
Interest rate	4.782%
Borrowings due July 2024 at 4.865% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 15.0
Interest rate	4.865%
Borrowings due August 2024 at 0.640% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 27.0
Interest rate	0.64%
Borrowings due September 2024 at 5.031% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 25.0
Interest rate	5.031%
Borrowings due May 2025 at 4.313% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 21.7
Interest rate	4.313%
Borrowings due June 2025 at 2.940% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 18.5
Interest rate	2.94%
Borrowings due September 2025 at 4.650% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 125.0
Interest rate	4.65%
Borrowings due October 2025 at 4.583% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.583%
Borrowings due October 2025 at 4.512% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.512%
Borrowings due October 2025 at 4.600% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 57.7
Interest rate	4.60%
Borrowings due November 2025 at 4.532% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.532%
Borrowings due January 2026 at 4.519% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.519%
Borrowings due January 2026 at 4.589% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.589%
Borrowings due January 2026 at 4.582% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.582%
Borrowings due May 2026 at 4.472% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 21.8
Interest rate	4.472%
Borrowings due May 2026 at 4.570% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.57%
Borrowings due December 2026 at 4.526% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 75.0
Interest rate	4.526%
Borrowings due April 2027 at 4.322% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.322%
Borrowings due May 2027 at 4.332% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 50.0
Interest rate	4.332%
Borrowings due June 2027 at 4.670% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 100.0
Interest rate	4.67%
Borrowings due June 2027 at 4.893% | Federal Home Loan Bank Advances
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Investment borrowings	$ 10.0
Interest rate	4.893%