DERIVATIVES - Derivative Gains and Losses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative contracts not designated as hedges | Asset Management
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	$ 8,362	$ 414,875
Derivative contracts not designated as hedges | Asset Management | Foreign Exchange Contracts and Options, and Foreign currency contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	9,549	414,290
Derivative contracts not designated as hedges | Asset Management | Other Derivatives
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(1,187)	585
Derivative contracts not designated as hedges | Insurance
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	146,722	0
Derivative contracts not designated as hedges | Insurance | Embedded derivatives
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	369,113	0
Derivative contracts not designated as hedges | Insurance | Equity market contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	104,021	0
Derivative contracts not designated as hedges | Insurance | Equity future contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(69,583)	0
Derivative contracts not designated as hedges | Insurance | Interest rate contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(266,731)	0
Derivative contracts not designated as hedges | Insurance | Credit risk contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(36)	0
Derivative contracts not designated as hedges | Insurance | Other Derivatives
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	9,938	0
Derivative contracts designated as hedges | Insurance | Gain (Loss) on Investments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	1,810	0
Derivative contracts designated as hedges | Insurance | Policy Benefits and Claims
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(8,403)	0
Derivative contracts designated as hedges | Insurance | Interest Expense
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(24,776)	0
Derivative contracts designated as hedges | Insurance | Foreign Exchange Contracts and Options | Gain (Loss) on Investments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	1,810	0
Derivative contracts designated as hedges | Insurance | Interest rate swap | Policy Benefits and Claims
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	(8,403)	0
Derivative contracts designated as hedges | Insurance | Interest rate swap | Interest Expense
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative gains (losses)	$ (24,776)	$ 0