INVESTMENTS - EQUITY-BASED AND TREASURY FUTURE CONTRACTS MARGIN (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Exchange Traded Future Contract [Line Items]
Cash and securities collateral for derivative contract	$ 2,135	$ 1,855
Cash and securities collateral	65	3
Securities sold under agreements to repurchase	1,900	$ 1,887
S&P 500, Russell 1000, NASDAQ 100 and Emerging Market Indices
Exchange Traded Future Contract [Line Items]
Initial margin requirements	203
Us Treasury Notes And Euro Dollar
Exchange Traded Future Contract [Line Items]
Initial margin requirements	53
Euro Stoxx, FTSE100, EAFE And Topix Indices
Exchange Traded Future Contract [Line Items]
Initial margin requirements	$ 21