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INVESTMENT SECURITIES (Summary of Investment Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Amortized cost
Available-for-sale	$ 10,379	$ 10,601
Held-to-maturity	9,059	9,669
Total investment securities	19,438	20,270
Gross unrealized gains
Available-for-sale	19	1
Held-to-maturity	89	2
Total investment securities	108	3
Gross unrealized losses
Available-for-sale	1,228	1,507
Held-to-maturity	42	289
Estimated fair value
Available-for-sale	9,170	9,095
Held-to-maturity, Estimated fair value	9,106	9,382
Total investment securities	18,276	18,477
Total investment securities	1,270	1,796
U.S. Treasury securities
Amortized cost
Available-for-sale	1,401	781
Gross unrealized gains
Available-for-sale	15	0
Gross unrealized losses
Available-for-sale	105	119
Estimated fair value
Available-for-sale	1,311	662
Agency securities
Amortized cost
Available-for-sale	349	441
Held-to-maturity	139	148
Gross unrealized gains
Available-for-sale	0	0
Held-to-maturity	0	0
Gross unrealized losses
Available-for-sale	17	26
Held-to-maturity	4	8
Estimated fair value
Available-for-sale	332	415
Held-to-maturity, Estimated fair value	135	140
Agency guaranteed mortgage-backed securities
Amortized cost
Available-for-sale	7,208	7,713
Held-to-maturity	8,643	9,202
Gross unrealized gains
Available-for-sale	4	1
Held-to-maturity	89	2
Gross unrealized losses
Available-for-sale	1,041	1,263
Held-to-maturity	28	263
Estimated fair value
Available-for-sale	6,171	6,451
Held-to-maturity, Estimated fair value	8,704	8,941
Small Business Administration loan-backed securities
Amortized cost
Available-for-sale	374	455
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	16	21
Estimated fair value
Available-for-sale	358	434
Municipal securities
Amortized cost
Available-for-sale	1,022	1,186
Held-to-maturity	277	319
Gross unrealized gains
Available-for-sale	0	0
Held-to-maturity	0	0
Gross unrealized losses
Available-for-sale	49	78
Held-to-maturity	10	18
Estimated fair value
Available-for-sale	973	1,108
Held-to-maturity, Estimated fair value	267	301
Other debt securities
Amortized cost
Available-for-sale	25	25
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	0	0
Estimated fair value
Available-for-sale	25	25
Available-for-sale, Unrealized Gains, Other | Maximum
Gross unrealized gains
Available-for-sale	$ 1	$ 1

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