INVESTMENTS IN VARIABLE INTEREST ENTITIES - BALANCE SHEET ITEMS (Details) - USD ($) $ in Millions	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Jan. 01, 2019
Assets:
Investments held by variable interest entities (net of allowance for credit losses of $27.7 at June 30, 2020; amortized cost: June 30, 2020 - $1,223.7; December 31, 2019 - $1,206.3)	$ 1,137.4	$ 1,178.7	$ 1,188.6
Cash and cash equivalents held by variable interest entities	36.8		74.7
Accrued investment income	205.3		205.9
Income tax assets, net	428.8	437.5	432.6	$ 630.9
Other assets	502.5		476.0
Total assets	33,979.5	$ 33,613.1	33,630.9	$ 31,436.7
Liabilities:
Other liabilities	788.3		750.2
Borrowings related to variable interest entities	1,152.2		1,152.5
Total liabilities	29,248.3		28,953.9
Variable Interest Entity, Primary Beneficiary
Assets:
Investments held by variable interest entities (net of allowance for credit losses of $27.7 at June 30, 2020; amortized cost: June 30, 2020 - $1,223.7; December 31, 2019 - $1,206.3)	1,137.4		1,188.6
Notes receivable of VIEs held by subsidiaries	(113.8)		(113.8)
Cash and cash equivalents held by variable interest entities	36.8		74.7
Accrued investment income	1.8		1.7
Income tax assets, net	23.4		8.0
Other assets	2.8		1.4
Total assets	1,088.4		1,160.6
Liabilities:
Other liabilities	24.2		38.4
Borrowings related to variable interest entities	1,152.2		1,152.5
Notes payable of VIEs held by subsidiaries	0.0		0.0
Total liabilities	1,176.4		1,190.9
Variable Interest Entity, Primary Beneficiary | VIEs
Assets:
Investments held by variable interest entities (net of allowance for credit losses of $27.7 at June 30, 2020; amortized cost: June 30, 2020 - $1,223.7; December 31, 2019 - $1,206.3)	1,137.4		1,188.6
Notes receivable of VIEs held by subsidiaries	0.0		0.0
Cash and cash equivalents held by variable interest entities	36.8		74.7
Accrued investment income	1.8		1.7
Income tax assets, net	23.4		8.0
Other assets	3.7		2.8
Total assets	1,203.1		1,275.8
Liabilities:
Other liabilities	27.1		42.8
Borrowings related to variable interest entities	1,152.2		1,152.5
Notes payable of VIEs held by subsidiaries	126.1		126.1
Total liabilities	1,305.4		1,321.4
Variable Interest Entity, Primary Beneficiary | Eliminations
Assets:
Investments held by variable interest entities (net of allowance for credit losses of $27.7 at June 30, 2020; amortized cost: June 30, 2020 - $1,223.7; December 31, 2019 - $1,206.3)	0.0		0.0
Notes receivable of VIEs held by subsidiaries	(113.8)		(113.8)
Cash and cash equivalents held by variable interest entities	0.0		0.0
Accrued investment income	0.0		0.0
Income tax assets, net	0.0		0.0
Other assets	(0.9)		(1.4)
Total assets	(114.7)		(115.2)
Liabilities:
Other liabilities	(2.9)		(4.4)
Borrowings related to variable interest entities	0.0		0.0
Notes payable of VIEs held by subsidiaries	(126.1)		(126.1)
Total liabilities	$ (129.0)		$ (130.5)