DEBT AND OTHER OBLIGATIONS - Non-Recourse Funding Obligations (Details) - USD ($)			12 Months Ended
	Jan. 15, 2016	Oct. 10, 2012	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2020
Debt Instrument [Line Items]
Non-recourse funding obligations			$ 2,197,000	$ 3,082,753,000
Payments under agreement			(329,949,000)	0	$ (63,890,000)
Amended Line Of Credit
Debt Instrument [Line Items]
Principal amount			1,000,000,000.0
Maximum borrowing capacity			$ 1,500,000,000
Facility fee rate			0.125%
Financing Agreement With Golden Gate And Syndicate Of Risk Takers
Debt Instrument [Line Items]
Term of financing agreement	18 years
Financing capacity under the agreement	$ 2,188,000,000
Golden Gate Captive Insurance Company (Golden Gate)
Debt Instrument [Line Items]
Non-recourse funding obligations				$ 2,028,000,000
Fixed annual rate				4.70%
Payments made under agreement			$ 0	$ 0
Golden Gate II Captive Insurance Company (Golden Gate II)
Debt Instrument [Line Items]
Non-recourse funding obligations				$ 274,955,000
Fixed annual rate				5.06%
Outstanding non-recourse funding obligations						$ 575,000,000
Non-recourse funding held by external parties						20,600,000
Non-recourse funding held by nonconsolidated affiliates						309,300,000
Non-recourse funding held by consolidated subsidiaries						245,100,000
Payments made under agreement			4,000,000.0	$ 1,700,000
Collateralized obligations under supper agreements			5,500,000	4,900,000
Repurchase of non-recourse funding obligations, at a discount			575,000,000
Golden Gate V Vermont Captive Insurance Company And Red Mountain L L C
Debt Instrument [Line Items]
Term of transaction		20 years
Maximum financing under transaction		$ 945,000,000
Red Mountain
Debt Instrument [Line Items]
Initial principal amount		275,000,000
Future maximum financing amount		$ 945,000,000
Principal balance of note			750,000,000
Payments under agreement			0
Golden Gate V Vermont Captive Insurance Company (Golden Gate V)
Debt Instrument [Line Items]
Non-recourse funding obligations				$ 777,527,000
Fixed annual rate				5.12%
PLC | Amended Line Of Credit
Debt Instrument [Line Items]
Outstanding balance			$ 190,000,000.0
Subordinated Debt | Subordinated Debentures 3.55 Percent Due 2038
Debt Instrument [Line Items]
Outstanding principal					$ 110,000,000.0
Interest rate					3.55%
Surplus Notes | Golden Gate | Steel City Notes
Debt Instrument [Line Items]
Amount of debt issued	2,188,000,000					$ 1,858,000,000
Surplus Notes | Steel City | Golden Gate Surplus Notes
Debt Instrument [Line Items]
Amount of debt issued	$ 2,188,000,000
Base Rate | Amended Line Of Credit
Debt Instrument [Line Items]
Variable rate			0.50%
LIBOR | Amended Line Of Credit
Debt Instrument [Line Items]
Variable rate			1.00%