INVESTMENTS - Credit Ratings (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 132.6	$ 218.4
Fair Value	$ 134.7	$ 224.0
AFS securities \| Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	100.00%	100.00%
AAA
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 72.4	$ 116.5
Fair Value	$ 73.1	$ 118.7
AAA \| AFS securities \| Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	54.30%	53.00%
AA+, AA, AA-, A-1
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 14.7	$ 22.7
Fair Value	$ 15.1	$ 23.3
AA+, AA, AA-, A-1 \| AFS securities \| Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	11.20%	10.40%
A+, A, A-
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 34.4	$ 57.5
Fair Value	$ 35.1	$ 59.4
A+, A, A- \| AFS securities \| Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	26.10%	26.50%
BBB+, BBB, BBB-
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 11.1	$ 21.7
Fair Value	$ 11.4	$ 22.6
BBB+, BBB, BBB- \| AFS securities \| Credit rating
Debt Securities, Available-for-sale [Line Items]
Concentration percentage	8.40%	10.10%

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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