INVESTMENT SECURITIES - Narrative (Details) $ in Millions	9 Months Ended
Sep. 30, 2024 USD ($) position	Dec. 31, 2023 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Book value	$ 20,279	$ 18,302
Fair value	$ 19,433	17,008
Minimum collateral as percentage of fair value of investment securities	102.00%
Securities lending invested collateral	$ 361
Fair value of non-cash securities lending	$ 148
Maximum individual state general bond obligation as a percentage of total debt securities (percent)	1.00%
Securities in unrealized loss positions, number of positions \| position	1,300
Securities, number of positions \| position	2,290
S&P AA- rating
Financing Receivable, Credit Quality Indicator [Line Items]
Percentage of debt securities considered to be of investment-grade (percent)	97.00%
Dispositions \| Gentiva Hospice
Financing Receivable, Credit Quality Indicator [Line Items]
Book value	$ 381	379
Fair value	$ 396	$ 398

Debt Securities, Available-for-sale, Securities, Number Of Positions

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Maximum Individual State General Bond Obligation, As Percentage Of Total Debt Securities

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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