INCOME TAXES - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Japan Tax Rate		28.20%	28.00%	28.00%	28.20%
U.S. federal statutory corporate income tax rate	21.00%		21.00%	21.00%	35.00%
Income Tax Expense, Gross, Continuing Operations, Adjustment of Deferred Tax Assets		$ 1,000.0
Income Tax Benefit, Gross, Continuing Operations, Adjustment of Deferred Tax Liabilities		2,900.0
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax Asset (Liability)		$ (1,900.0)		$ 0.4
Deferred Tax Assets, Valuation Allowance			$ 1,340.0	738.0
Non-life operating loss carryforwards, limitations			only 35% of non-life operating losses can be offset against life insurance taxable income each year
Operating Loss Carryforwards			$ 99.0
Unrecognized tax benefit, deductibility highly certain, timing uncertain			15.0	14.0
Unrecognized tax benefits, permanent uncertainties			2.0
Unrecognized tax benefits, interest and penalties expense			1.0	1.0	$ 1.0
Unrecognized tax benefits, accrued interest and penalties			2.0	$ 2.0
Anticipatory Foreign Tax Credit
Income Taxes [Line Items]
Deferred Tax Assets, Valuation Allowance			1,022.0
Deferred Foreign Tax Credit
Income Taxes [Line Items]
Deferred Tax Assets, Valuation Allowance			318.0
Capital Loss Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount			161.0
Expiring in 2039
Income Taxes [Line Items]
Operating Loss Carryforwards			31.0
No expiration
Income Taxes [Line Items]
Operating Loss Carryforwards			68.0
Expiring in 2023 | Capital Loss Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount			65.0
Expiring in 2024 | Capital Loss Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount			$ 96.0