OFFSETTING OF ASSETS AND LIABILITIES - Schedule of Derivative Instruments by Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivative instruments by assets
Fair value of non-cash collateral	$ 34,400	$ 45,000
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives Not Subject to a master netting arrangement	823,514	414,827
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	823,514	414,827
Derivative Asset, Not Offset, Policy Election Deduction	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	255,776	99,199
Net Amount	304,493	245,306
Free-Standing derivatives
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives	630,474	263,349
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	630,474	263,349
Derivative Asset, Not Subject to Master Netting Arrangement Deduction	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	255,776	99,199
Net Amount	111,453	93,828
Total derivatives, subject to a master netting arrangement or similar arrangement
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives	630,474	263,349
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	630,474	263,349
Derivative Asset, Not Subject to Master Netting Arrangement Deduction	263,245	70,322
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	255,776	99,199
Net Amount	111,453	93,828
Embedded derivative - Modco reinsurance treaties
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives Not Subject to a master netting arrangement	30,600	7,072
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	30,600	7,072
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	0	0
Net Amount	30,600	7,072
Embedded derivative - GLWB
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives Not Subject to a master netting arrangement	59,248	54,221
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	59,248	54,221
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	0	0
Net Amount	59,248	54,221
Derivatives with PLC
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives Not Subject to a master netting arrangement	103,192	90,049
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	103,192	90,049
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	0	0
Net Amount	103,192	90,049
Other
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives Not Subject to a master netting arrangement	0	136
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	0	136
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	0	0
Net Amount	0	136
Total derivatives, not subject to a master netting arrangement or similar arrangement
Offsetting of Assets
Gross Amounts of Recognized Assets, Derivatives Not Subject to a master netting arrangement	193,040	151,478
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts of Assets Presented in the Statement of Financial Position	193,040	151,478
Derivative Asset, Not Offset, Policy Election Deduction	0	0
Gross Amounts Not Offset in the Statement of Financial Position, Cash Collateral Received	0	0
Net Amount	$ 193,040	$ 151,478

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