INVESTMENTS - Investment Exposures Individually Exceeded 10% of Shareholders' Equity (Details) - Japan National Government - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Summary of Investment Holdings [Line Items]
Credit Rating	[1]	A+	A+
Amortized Cost	[1]	$ 51,775	$ 51,207
Fair Value	[1]	$ 62,275	$ 59,945

[1] Japan Government Bonds (JGBs) or JGB-backed securities