OTHER COMPREHENSIVE INCOME - Activity/Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
After-tax
Unrealized gains (losses) on available-for-sale securities arising during the period, net of hedges	$ 167	$ 761	$ 706	$ 418
Reclassification adjustment for realized net losses included in net income	8	46	89	154
Other comprehensive income, net of tax	175	807	795	572
Unrealized gains and (losses) on debt securities
Pretax
Other comprehensive income (loss) before reclassifications	197	573	591	310
Reclassification adjustment for cash flow hedges included in net income	2	4	69	9
Tax (expense) benefit
OCI before reclassification, tax (expense) benefit	(46)	(131)	(139)	(70)
Reclassification adjustment for realized net losses included in net income	0	(1)	(16)	(2)
After-tax
Unrealized gains (losses) on available-for-sale securities arising during the period, net of hedges	151	442	452	240
Reclassification adjustment for realized net losses included in net income	2	3	53	7
Other comprehensive income, net of tax	153	445	505	247
Net change related to cash flow hedges on loans
Pretax
Other comprehensive income (loss) before reclassifications	23	412	324	231
Reclassification adjustment for cash flow hedges included in net income	7	55	46	190
Tax (expense) benefit
OCI before reclassification, tax (expense) benefit	(6)	(95)	(77)	(53)
Reclassification adjustment for realized net losses included in net income	(1)	(12)	(10)	(44)
After-tax
Unrealized gains (losses) on available-for-sale securities arising during the period, net of hedges	17	317	247	178
Reclassification adjustment for realized net losses included in net income	6	43	36	146
Other comprehensive income, net of tax	23	360	283	324
Net change related to cash flow hedges on loans | Cash Flow Hedges
Pretax
Other comprehensive income (loss), pretax	30	467	370	421
Tax (expense) benefit
Total other comprehensive income (loss), tax (expense) benefit	(7)	(107)	(87)	(97)
After-tax
Other comprehensive income, net of tax	23	360	283	324
Accumulated foreign currency adjustment
Pretax
Other comprehensive income (loss), pretax	(2)	2	7
Tax (expense) benefit
Total other comprehensive income (loss), tax (expense) benefit	1	0	(1)
After-tax
Other comprehensive income, net of tax	(1)	2	6
Unrealized losses for pension and other post-retirement obligations
Pretax
Other comprehensive income (loss), pretax		1	1	2
Tax (expense) benefit
Total other comprehensive income (loss), tax (expense) benefit		(1)	0	(1)
After-tax
Unrealized gains (losses) on available-for-sale securities arising during the period, net of hedges	0	0	1	0
Reclassification adjustment for realized net losses included in net income	0	0	0	1
Other comprehensive income, net of tax	0	0	1	1
AOCI
Pretax
Other comprehensive income (loss), pretax	227	1,047	1,038	742
Tax (expense) benefit
Total other comprehensive income (loss), tax (expense) benefit	(52)	(240)	(243)	(170)
After-tax
Other comprehensive income, net of tax	175	807	795	572
Debt securities | Unrealized gains and (losses) on debt securities
Pretax
Other comprehensive income (loss), pretax	199	577	660	319
Tax (expense) benefit
Total other comprehensive income (loss), tax (expense) benefit	(46)	(132)	(155)	(72)
After-tax
Other comprehensive income, net of tax	$ 153	$ 445	$ 505	$ 247