POLICY LIABILITIES - Changes in Liability for Unpaid Policy Claims (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Liability for Unpaid Claims and Claims Expenses
Net balance, beginning of period	$ 4,392
Less claims paid during the period on claims incurred during:
Net balance, end of period	4,630
Total liability for unpaid policy claims	4,630	$ 4,230
Health insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of period	3,884	3,707
Less reinsurance recoverables	30	27
Net balance, beginning of period	3,854	3,680
Add claims incurred during the period related to:
Current year	1,842	1,737
Prior years	(192)	(111)
Total incurred	1,650	1,626
Less claims paid during the period on claims incurred during:
Current year	518	505
Prior years	1,116	1,055
Total paid	1,634	1,560
Effect of foreign exchange rate changes on unpaid claims	142	80
Net balance, end of period	4,012	3,826
Add reinsurance recoverables	31	29
Total liability for unpaid policy claims	4,043	3,855
Life insurance
Less claims paid during the period on claims incurred during:
Total liability for unpaid policy claims	$ 587	$ 375