INVESTMENTS - Equity Securities, FV-NI (Details) $ in Millions	Mar. 31, 2018 USD ($)
Equity Securities, FV-NI [Line Items]
Fair Value	$ 1,108	[1],[2]
Yen-denominated
Equity Securities, FV-NI [Line Items]
Fair Value	711
Dollar-denominated
Equity Securities, FV-NI [Line Items]
Fair Value	397
Equity securities
Equity Securities, FV-NI [Line Items]
Perpetual Securities, Fair Value	$ 71

[1] Includes perpetual securities

[2] Includes perpetual securities ($71 at fair value)