POLICY LIABILITIES - Changes in Liability for Unpaid Policy Claims (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of year	$ 4,659	$ 4,584
Net balance, beginning of year	4,659
Less claims paid during the year on claims incurred during:
Net balance, end of year	5,187	4,659
Total liability for unpaid policy claims	5,187	4,659	$ 4,584
Zurich North America's U.S. Corporate Life and Pensions business
Less claims paid during the year on claims incurred during:
Liability for Unpaid Claims and Claims Adjustment Expense, Business Acquisitions	99	0	0
Health insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of year	3,968	3,952	3,884
Less reinsurance recoverables	30	27	30
Net balance, beginning of year	3,938	3,925	3,854
Add claims incurred during the year related to:
Current year	7,179	7,216	7,101
Prior years	(540)	(552)	(563)
Total incurred	6,639	6,664	6,538
Less claims paid during the year on claims incurred during:
Current year	4,488	4,715	4,612
Prior years	1,966	1,965	1,898
Total paid	6,454	6,680	6,510
Effect of foreign exchange rate changes on unpaid claims	128	29	43
Net balance, end of year	4,350	3,938	3,925
Add reinsurance recoverables	39	30	27
Total liability for unpaid policy claims	4,389	3,968	3,952
Life insurance
Liability for Unpaid Claims and Claims Expenses
Unpaid supplemental health claims, beginning of year	691	632
Less claims paid during the year on claims incurred during:
Total liability for unpaid policy claims	$ 798	$ 691	$ 632