MONY CLOSED BLOCK OF BUSINESS - Summary of Financial Information of the Policyholder Dividend Obligation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Closed block liabilities
Future policy benefits, policyholders’ account balances and other policyholder liabilities	$ 5,760,621	$ 5,791,867
Policyholder dividend obligation	0	160,712	$ 41,180	$ 31,932
Other liabilities	34,796	30,764
Total closed block liabilities	5,795,417	5,983,343
Closed block assets
Fixed maturities, available-for-sale, at fair value	4,497,521	4,669,856
Mortgage loans on real estate	107,826	108,934
Policy loans	692,632	700,769
Cash	39,464	31,182
Other assets	113,120	122,637
Total closed block assets	5,450,563	5,633,378
Excess of reported closed block liabilities over closed block assets	344,854	349,965
Portion of above representing accumulated other comprehensive income:
Net unrealized investment gains (losses) net of policyholder dividend obligation: $(162,429) and $(13,429); and net of income tax: $34,911 and $2,820	(3,014)	0
Future earnings to be recognized from closed block assets and closed block liabilities	341,840	349,965
Net unrealized investment gains (losses) allocated to policyholder dividend obligation, net of deferred tax benefits	(162,429)	(13,429)
Net unrealized investment gains (losses), income tax	$ 34,911	$ 2,820