POLICY LIABILITIES - Changes in Liability for Unpaid Policy Claims (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability for Unpaid Claims and Claims Expenses
Net balance, beginning of period	$ 4,659
Less claims paid during the period on claims incurred during:
Net balance, end of period	4,693
Total liability for unpaid policy claims	4,693	$ 4,625
Health insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of period	3,968	3,952
Less reinsurance recoverables	31	29
Net balance, beginning of period	3,937	3,923
Add claims incurred during the period related to:
Current year	1,837	1,825
Prior years	(136)	(167)
Total incurred	1,701	1,658
Less claims paid during the period on claims incurred during:
Current year	556	506
Prior years	1,144	1,137
Total paid	1,700	1,643
Effect of foreign exchange rate changes on unpaid claims	12	0
Net balance, end of period	3,950	3,938
Add reinsurance recoverables	33	29
Total liability for unpaid policy claims	3,983	3,967
Life insurance
Less claims paid during the period on claims incurred during:
Total liability for unpaid policy claims	$ 710	$ 658