INVESTMENTS - Investment Exposures Individually Exceeded 10% of Shareholders' Equity (Details) - Japan National Government - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Summary of Investment Holdings [Line Items]
Credit Rating	[1]	A	A
Amortized Cost	[1]	$ 54,465	$ 48,399
Fair Value	[1]	$ 63,576	$ 56,532

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