FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Cash and cash equivalents:
Held by variable interest entities	$ 51.0	$ 74.7
Fair Value, Measurements, Recurring | Total estimated fair value
Assets:
Mortgage loans	1,496.5	1,651.4
Policy loans	123.6	124.5
Other invested assets:
Company-owned life insurance	206.7	194.0
Cash and cash equivalents:
Unrestricted	735.6	580.0
Held by variable interest entities	51.0	74.7
Liabilities:
Policyholder account liabilities	12,357.5	12,132.3
Investment borrowings	1,648.0	1,647.9
Borrowings related to variable interest entities	1,124.6	1,142.1
Notes payable – direct corporate obligations	1,148.8	1,117.2
Fair Value, Measurements, Recurring | Total carrying amount
Assets:
Mortgage loans	1,444.9	1,566.1
Policy loans	123.6	124.5
Other invested assets:
Company-owned life insurance	206.7	194.0
Cash and cash equivalents:
Unrestricted	735.6	580.0
Held by variable interest entities	51.0	74.7
Liabilities:
Policyholder account liabilities	12,357.5	12,132.3
Investment borrowings	1,642.9	1,644.3
Borrowings related to variable interest entities	1,152.0	1,152.5
Notes payable – direct corporate obligations	990.1	989.1
Fair Value, Measurements, Recurring | Quoted prices in active markets for identical assets or liabilities (Level 1)
Assets:
Mortgage loans	0.0	0.0
Policy loans	0.0	0.0
Other invested assets:
Company-owned life insurance	0.0	0.0
Cash and cash equivalents:
Unrestricted	735.5	579.9
Held by variable interest entities	51.0	74.7
Liabilities:
Policyholder account liabilities	0.0	0.0
Investment borrowings	0.0	0.0
Borrowings related to variable interest entities	0.0	0.0
Notes payable – direct corporate obligations	0.0	0.0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets:
Mortgage loans	0.0	0.0
Policy loans	0.0	0.0
Other invested assets:
Company-owned life insurance	206.7	194.0
Cash and cash equivalents:
Unrestricted	0.1	0.1
Held by variable interest entities	0.0	0.0
Liabilities:
Policyholder account liabilities	0.0	0.0
Investment borrowings	1,648.0	1,647.9
Borrowings related to variable interest entities	1,124.6	1,142.1
Notes payable – direct corporate obligations	1,148.8	1,117.2
Fair Value, Measurements, Recurring | Significant unobservable inputs  (Level 3)
Assets:
Mortgage loans	1,496.5	1,651.4
Policy loans	123.6	124.5
Other invested assets:
Company-owned life insurance	0.0	0.0
Cash and cash equivalents:
Unrestricted	0.0	0.0
Held by variable interest entities	0.0	0.0
Liabilities:
Policyholder account liabilities	12,357.5	12,132.3
Investment borrowings	0.0	0.0
Borrowings related to variable interest entities	0.0	0.0
Notes payable – direct corporate obligations	$ 0.0	$ 0.0