FAIR VALUES OF ASSETS AND LIABILITIES - Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Assets measured at fair value on a recurring basis
Trading account securities	$ 199	$ 63
Fair Value	35,557	26,132
Other securities	64	42
Loans held for sale	1,068	885
Loans Accounted for Under FVO	166	167
MSRs	735	593
Gross amounts of recognized assets	561	507
Derivative assets netting	(295)	(260)
Derivative assets	266	247
Assets held in trust for deferred compensation plans	212	216
Liabilities measured at fair value on a recurring basis
Short-term borrowings	283	138
Long-term debt	1,434	1,161
Gross amounts of recognized liabilities	572	519
Gross amounts offset in the unaudited consolidated balance sheets	(175)	(169)
Derivative liabilities	397	350
U.S. Treasury
Assets measured at fair value on a recurring basis
Fair Value	8,486	4,635
Residential MBS
Assets measured at fair value on a recurring basis
Fair Value	12,597	9,669
Residential CMO
Assets measured at fair value on a recurring basis
Fair Value	6,448	5,197
Commercial MBS
Assets measured at fair value on a recurring basis
Fair Value	2,705	1,831
Other agencies
Assets measured at fair value on a recurring basis
Fair Value	519	150
Municipal securities
Assets measured at fair value on a recurring basis
Fair Value	4,338	4,143
Corporate debt
Assets measured at fair value on a recurring basis
Fair Value	176	178
Asset-backed securities
Assets measured at fair value on a recurring basis
Fair Value	182	221
Private-label CMO
Assets measured at fair value on a recurring basis
Fair Value	96	98
Other securities/sovereign debt
Assets measured at fair value on a recurring basis
Fair Value	10	10
Level 1
Assets measured at fair value on a recurring basis
Trading account securities	30	0
Fair Value	8,486	4,635
Other securities	29	30
Loans held for sale	0	0
Loans Accounted for Under FVO	0	0
MSRs	0	0
Gross amounts of recognized assets	0	0
Assets held in trust for deferred compensation plans	212	216
Liabilities measured at fair value on a recurring basis
Short-term borrowings	261	131
Long-term debt	0	0
Gross amounts of recognized liabilities	0	0
Level 1 | U.S. Treasury
Assets measured at fair value on a recurring basis
Fair Value	8,486	4,635
Level 1 | Residential MBS
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Residential CMO
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Commercial MBS
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Other agencies
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Municipal securities
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Corporate debt
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Asset-backed securities
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Private-label CMO
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 1 | Other securities/sovereign debt
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 2
Assets measured at fair value on a recurring basis
Trading account securities	169	63
Fair Value	22,781	17,389
Other securities	35	12
Loans held for sale	1,068	885
Loans Accounted for Under FVO	105	105
MSRs	0	0
Gross amounts of recognized assets	551	499
Assets held in trust for deferred compensation plans	0	0
Liabilities measured at fair value on a recurring basis
Short-term borrowings	22	7
Long-term debt	1,434	1,161
Gross amounts of recognized liabilities	568	514
Level 2 | U.S. Treasury
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 2 | Residential MBS
Assets measured at fair value on a recurring basis
Fair Value	12,597	9,669
Level 2 | Residential CMO
Assets measured at fair value on a recurring basis
Fair Value	6,448	5,197
Level 2 | Commercial MBS
Assets measured at fair value on a recurring basis
Fair Value	2,705	1,831
Level 2 | Other agencies
Assets measured at fair value on a recurring basis
Fair Value	519	150
Level 2 | Municipal securities
Assets measured at fair value on a recurring basis
Fair Value	87	82
Level 2 | Corporate debt
Assets measured at fair value on a recurring basis
Fair Value	176	178
Level 2 | Asset-backed securities
Assets measured at fair value on a recurring basis
Fair Value	163	193
Level 2 | Private-label CMO
Assets measured at fair value on a recurring basis
Fair Value	76	79
Level 2 | Other securities/sovereign debt
Assets measured at fair value on a recurring basis
Fair Value	10	10
Level 3
Assets measured at fair value on a recurring basis
Trading account securities	0	0
Fair Value	4,290	4,108
Other securities	0	0
Loans held for sale	0	0
Loans Accounted for Under FVO	61	62
MSRs	735	593
Gross amounts of recognized assets	10	8
Assets held in trust for deferred compensation plans	0	0
Liabilities measured at fair value on a recurring basis
Short-term borrowings	0	0
Long-term debt	0	0
Gross amounts of recognized liabilities	4	5
Level 3 | U.S. Treasury
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 3 | Residential MBS
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 3 | Residential CMO
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 3 | Commercial MBS
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 3 | Other agencies
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 3 | Municipal securities
Assets measured at fair value on a recurring basis
Fair Value	4,251	4,061
Level 3 | Corporate debt
Assets measured at fair value on a recurring basis
Fair Value	0	0
Level 3 | Asset-backed securities
Assets measured at fair value on a recurring basis
Fair Value	19	28
Level 3 | Private-label CMO
Assets measured at fair value on a recurring basis
Fair Value	20	19
Level 3 | Other securities/sovereign debt
Assets measured at fair value on a recurring basis
Fair Value	$ 0	$ 0