INVESTMENT SECURITIES - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($) position	Dec. 31, 2024 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Book value	$ 18,040	$ 20,018
Fair value	$ 17,176	18,635
Minimum collateral as percentage of fair value of investment securities	102.00%
Securities lending invested collateral	$ 560	418
Non-cash securities lending, fair value	$ 274	127
Maximum individual state general bond obligation as a percentage of total debt securities (as percent)	1.00%
Securities in unrealized loss positions, number of positions | position	1,200
Securities, number of positions | position	2,190
S&P AA- rating
Financing Receivable, Credit Quality Indicator [Line Items]
Percentage of debt securities considered to be of investment-grade (as percent)	97.00%
Dispositions | Gentiva Hospice
Financing Receivable, Credit Quality Indicator [Line Items]
Book value	$ 381	381
Fair value	$ 390	$ 396