INVESTMENTS - EQUITY-BASED AND TREASURY FUTURE CONTRACTS MARGIN (Details) - USD ($) $ in Millions	Jan. 03, 2017	Mar. 31, 2018	Dec. 31, 2017
Exchange Traded Future Contract [Line Items]
Cash and securities collateral for derivative contract		$ 1,824	$ 1,855
Collateralized derivative transactions		2	2
Cash and securities collateral		7	3
Reduction of derivative gross assets	$ 13
Securities sold under agreements to repurchase		1,904	$ 1,887
S&P 500, Russell 1000, NASDAQ 100 and Emerging Market Indices
Exchange Traded Future Contract [Line Items]
Initial margin requirements		121
Us Treasury Notes And Euro Dollar
Exchange Traded Future Contract [Line Items]
Initial margin requirements		23
Euro Stoxx, FTSE100, EAFE And Topix Indices
Exchange Traded Future Contract [Line Items]
Initial margin requirements		$ 12