COMMITMENTS AND CONTINGENT LIABILITIES - Additional Information (Detail) $ in Millions, ¥ in Billions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) agreements	Dec. 31, 2017 JPY (¥) 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
Operating Leases, lease terms		expire in various years through 2028	expire in various years through 2028
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, discounted amount of insurance-related assessment liability, realization period for associated asset offsets (in years)	5
Loss contingency, loss in period	$ 14
Mainframe and server computer operations and support
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		3 years	3 years
Outsourcing agreements, aggregate remaining cost		$ 243	¥ 27.5
Technology and consulting company application maintenance and development services
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		4 years	4 years
Outsourcing agreements, aggregate remaining cost		$ 80	¥ 9.0
Management consulting and technology services company application maintenance and development services
Commitments and Contingencies Disclosure [Line Items]
Outsourcing agreements, remaining term		4 years	4 years
Outsourcing agreements, aggregate remaining cost		$ 124	¥ 14.0
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		$ 26	¥ 3.0
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		$ 65	¥ 7.4