POLICY LIABILITIES - Changes in Liability for Unpaid Policy Claims (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Liability for Unpaid Claims and Claims Expenses
Net balance, beginning of period	$ 4,584
Less claims paid during the period on claims incurred during:
Net balance, end of period	4,625
Total liability for unpaid policy claims	4,625	$ 4,630
Health insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of period	3,952	3,884
Less reinsurance recoverables	29	30
Net balance, beginning of period	3,923	3,854
Add claims incurred during the period related to:
Current year	1,825	1,842
Prior years	(167)	(192)
Total incurred	1,658	1,650
Less claims paid during the period on claims incurred during:
Current year	506	518
Prior years	1,137	1,116
Total paid	1,643	1,634
Effect of foreign exchange rate changes on unpaid claims	0	142
Net balance, end of period	3,938	4,012
Add reinsurance recoverables	29	31
Total liability for unpaid policy claims	3,967	4,043
Life insurance
Less claims paid during the period on claims incurred during:
Total liability for unpaid policy claims	$ 658	$ 587