FAIR VALUES OF ASSETS AND LIABILITIES - Level 3 Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024
Derivative instruments
Opening balance	$ 6	$ 3	$ 3	$ 2
Transfers into Level 3	0	0
Transfers out of Level 3	(13)	(7)
Included in earnings	$ 13
Included in earnings, location	Noninterest income
Included in OCI	$ 0	0
Purchases/originations	0	0
Repayments	0	0
Settlements	2	3
Closing balance	6	3
Change in unrealized gains (losses) for the period included in earnings for assets held at end of the reporting date	1	3
Cadence
Derivative instruments
Purchases/originations	1
Mortgage banking income
Derivative instruments
Included in earnings		10
Other noninterest income
Derivative instruments
Included in earnings		(5)
MSRs
Level 3 Assets Roll Forward:
Opening balance	593	573
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains (losses) for the period:
Included in earnings	$ (5)
Included in earnings, location	Noninterest income
Included in OCI	$ 0	0
Purchases/originations	28	20
Repayments	0	0
Settlements	(21)	(14)
Closing balance	735	564	593	573
Change in unrealized gains (losses) for the period included in earnings for assets held at end of the reporting date	(5)	(15)
MSRs | Cadence
Total gains (losses) for the period:
Purchases/originations	140
MSRs | Mortgage banking income
Total gains (losses) for the period:
Included in earnings		(15)
MSRs | Other noninterest income
Total gains (losses) for the period:
Included in earnings		0
Municipal securities
Level 3 Assets Roll Forward:
Opening balance	4,061	3,954
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains (losses) for the period:
Included in earnings	$ 0
Included in earnings, location	Noninterest income
Included in OCI	$ (26)	5
Purchases/originations	326	218
Repayments	0	0
Settlements	(110)	(248)
Closing balance	4,251	3,929	4,061	3,954
Change in unrealized gains (losses) for the period included in earnings for assets held at end of the reporting date	(26)	4
Municipal securities | Cadence
Total gains (losses) for the period:
Purchases/originations	0
Municipal securities | Mortgage banking income
Total gains (losses) for the period:
Included in earnings		0
Municipal securities | Other noninterest income
Total gains (losses) for the period:
Included in earnings		0
Private-label CMO
Level 3 Assets Roll Forward:
Opening balance	19	21
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains (losses) for the period:
Included in earnings	$ 0
Included in earnings, location	Noninterest income
Included in OCI	$ 0	0
Purchases/originations	0	0
Repayments	0	0
Settlements	1	1
Closing balance	20	22	19	21
Change in unrealized gains (losses) for the period included in earnings for assets held at end of the reporting date	0	0
Private-label CMO | Cadence
Total gains (losses) for the period:
Purchases/originations	0
Private-label CMO | Mortgage banking income
Total gains (losses) for the period:
Included in earnings		0
Private-label CMO | Other noninterest income
Total gains (losses) for the period:
Included in earnings		0
Asset-backed securities
Level 3 Assets Roll Forward:
Opening balance	28	49
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Total gains (losses) for the period:
Included in earnings	$ 0
Included in earnings, location	Noninterest income
Included in OCI	$ 0	0
Purchases/originations	0	0
Repayments	0	0
Settlements	(9)	(2)
Closing balance	19	47	28	49
Change in unrealized gains (losses) for the period included in earnings for assets held at end of the reporting date	0	0
Asset-backed securities | Cadence
Total gains (losses) for the period:
Purchases/originations	0
Asset-backed securities | Mortgage banking income
Total gains (losses) for the period:
Included in earnings		0
Asset-backed securities | Other noninterest income
Total gains (losses) for the period:
Included in earnings		0
Loans held for investment
Level 3 Assets Roll Forward:
Opening balance	62	61
Transfers into Level 3	1	3
Transfers out of Level 3	0	0
Total gains (losses) for the period:
Included in earnings	$ 0
Included in earnings, location	Noninterest income
Included in OCI	$ 0	0
Purchases/originations	0	0
Repayments	(2)	(1)
Settlements	0	0
Closing balance	61	63	$ 62	$ 61
Change in unrealized gains (losses) for the period included in earnings for assets held at end of the reporting date	0	0
Loans held for investment | Cadence
Total gains (losses) for the period:
Purchases/originations	$ 0
Loans held for investment | Mortgage banking income
Total gains (losses) for the period:
Included in earnings		0
Loans held for investment | Other noninterest income
Total gains (losses) for the period:
Included in earnings		$ 0