COMMITMENTS AND CONTINGENT LIABILITIES - Additional Information (Detail) $ in Millions, ¥ in Billions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2020 JPY (¥) agreements	Dec. 31, 2020 USD ($) agreements
Commitments and Contingencies Disclosure [Line Items]
Number of operating service agreements, technology and consulting | agreements		2	2
Number of operating service agreements, management consulting and technology | agreements		1	1
Number of operating service agreements, information technology and data services | agreements		2	2
Loss contingency accrual, insurance-related assessment, discount rate	4.25%
Loss contingency, discounted amount of insurance-related assessment liability	$ 62
Loss contingency, undiscounted amount of insurance-related assessment liability	94
Loss contingency, insurance related assessment, discounted amount of premium tax offset	48
Loss contingency, insurance-related assessment, undiscounted amount of premium tax offset	74
Loss contingency, loss in period	$ 14
Mainframe and server computer operations and support
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		2 years	2 years
Outsourcing agreements, aggregate remaining cost		¥ 17.5	$ 169
Technology and consulting company application maintenance and development services
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		3 years	3 years
Outsourcing agreements, aggregate remaining cost		¥ 4.6	$ 45
Management consulting and technology services company application maintenance and development services
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		1 year	1 year
Outsourcing agreements, aggregate remaining cost		¥ 3.3	$ 32
Information technology and data services company application maintenance and development services first agreement
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		2 years	2 years
Outsourcing agreements, aggregate remaining cost		¥ 3.0	$ 29
Information technology and data services company application maintenance and development services second agreement
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		5 years	5 years
Outsourcing agreements, aggregate remaining cost		¥ 13.7	$ 133