INVESTMENT SECURITIES (Summary of Investment Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Amortized cost
Available-for-sale	$ 10,731	$ 11,759
Held-to-maturity	9,857	10,382
Total investment securities	20,588	22,141
Gross unrealized gains
Available-for-sale	2	0
Held-to-maturity	215	156
Total investment securities	217	156
Gross unrealized losses
Available-for-sale	1,238	1,459
Held-to-maturity	48	72
Estimated fair value
Available-for-sale	9,495	10,300
Held-to-maturity, Estimated fair value	10,024	10,466
Total investment securities	19,519	20,766
Total investment securities	1,286	1,531
U.S. Treasury securities
Amortized cost
Available-for-sale	580	585
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	90	93
Estimated fair value
Available-for-sale	490	492
Agency securities
Amortized cost
Available-for-sale	478	663
Held-to-maturity	149	93
Gross unrealized gains
Available-for-sale	0	0
Held-to-maturity	0	0
Gross unrealized losses
Available-for-sale	20	33
Held-to-maturity	5	6
Estimated fair value
Available-for-sale	458	630
Held-to-maturity, Estimated fair value	144	87
Agency guaranteed mortgage-backed securities
Amortized cost
Available-for-sale	7,914	8,530
Held-to-maturity	9,384	9,935
Gross unrealized gains
Available-for-sale	2	0
Held-to-maturity	215	156
Gross unrealized losses
Available-for-sale	1,047	1,239
Held-to-maturity	29	50
Estimated fair value
Available-for-sale	6,869	7,291
Held-to-maturity, Estimated fair value	9,570	10,041
Small Business Administration loan-backed securities
Amortized cost
Available-for-sale	483	571
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	18	25
Estimated fair value
Available-for-sale	465	546
Municipal securities
Amortized cost
Available-for-sale	1,251	1,385
Held-to-maturity	324	354
Gross unrealized gains
Available-for-sale	0	0
Held-to-maturity	0	0
Gross unrealized losses
Available-for-sale	62	67
Held-to-maturity	14	16
Estimated fair value
Available-for-sale	1,189	1,318
Held-to-maturity, Estimated fair value	310	338
Other debt securities
Amortized cost
Available-for-sale	25	25
Gross unrealized gains
Available-for-sale	0	0
Gross unrealized losses
Available-for-sale	1	2
Estimated fair value
Available-for-sale	$ 24	23
Available-for-sale, Unrealized Gains, Other
Gross unrealized gains
Available-for-sale		$ 1