INVESTMENTS - Equity Securities (Details) $ in Millions	Sep. 30, 2018 USD ($)
Equity Securities, FV-NI [Line Items]
Fair Value	$ 1,059	[1],[2]
Yen-denominated
Equity Securities, FV-NI [Line Items]
Fair Value	707
Dollar-denominated
Equity Securities, FV-NI [Line Items]
Fair Value	352
Equity securities
Equity Securities, FV-NI [Line Items]
Perpetual securities, fair value	$ 66

[1] Includes perpetual securities ($66 at fair value)

[2] Includes perpetual securities