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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Japan Tax Rate		28.20%	28.00%	28.20%	28.80%
U.S. federal statutory corporate income tax rate	21.00%		21.00%	35.00%	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		657.0	$ 738.0	$ 657.0
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			$ 21.0
Unrecognized tax benefit, deductibility highly certain, timing uncertain		13.0	14.0	13.0
Unrecognized tax benefits, permanent uncertainties			1.0
Unrecognized tax benefits, interest and penalties expense			1.0	1.0	$ 13.0
Unrecognized tax benefits, accrued interest and penalties		$ 2.0	2.0	$ 2.0
Anticipatory Foreign Tax Credit
Income Taxes [Line Items]
Deferred Tax Assets, Valuation Allowance			577.0
Deferred Foreign Tax Credit
Income Taxes [Line Items]
Deferred Tax Assets, Valuation Allowance			161.0
Capital Loss Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount			22.0
Expiring In Twenty Twenty One | Capital Loss Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount			4.0
Expiring In Twenty Twenty Three | Capital Loss Carryforward
Income Taxes [Line Items]
Tax Credit Carryforward, Amount			$ 18.0