INVESTMENT SECURITIES (Summary of Amount of Gross Unrealized Losses for Debt Securities and Estimated Fair Value) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 Months	$ 0	$ 3
Available-for-sale, 12 Months or more	1,228	1,504
Available-for-sale, total	1,228	1,507
Available-for-sale, less than 12 Months, estimated fair value	131	390
Available-for-sale, 12 months or more, estimated fair value	7,596	8,230
Available-for-sale, total, estimated fair value	7,727	8,620
U.S. Treasury securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 Months	0	3
Available-for-sale, 12 Months or more	105	116
Available-for-sale, total	105	119
Available-for-sale, less than 12 Months, estimated fair value	0	198
Available-for-sale, 12 months or more, estimated fair value	296	285
Available-for-sale, total, estimated fair value	296	483
Agency securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	17	26
Available-for-sale, total	17	26
Available-for-sale, less than 12 Months, estimated fair value	7	3
Available-for-sale, 12 months or more, estimated fair value	320	403
Available-for-sale, total, estimated fair value	327	406
Agency guaranteed mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	1,041	1,263
Available-for-sale, total	1,041	1,263
Available-for-sale, less than 12 Months, estimated fair value	6	86
Available-for-sale, 12 months or more, estimated fair value	5,846	6,171
Available-for-sale, total, estimated fair value	5,852	6,257
Small Business Administration loan-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	16	21
Available-for-sale, total	16	21
Available-for-sale, less than 12 Months, estimated fair value	32	35
Available-for-sale, 12 months or more, estimated fair value	321	387
Available-for-sale, total, estimated fair value	353	422
Municipal securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	49	78
Available-for-sale, total	49	78
Available-for-sale, less than 12 Months, estimated fair value	86	68
Available-for-sale, 12 months or more, estimated fair value	813	984
Available-for-sale, total, estimated fair value	$ 899	$ 1,052

ZIONS BANCORPORATION, NATIONAL ASSOCIATION /UT/ 10-Q