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Segment Information - Reconciliation of Net Income (Loss) Attributable to AGL to Segment Adjusted Operating Income (Loss) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Segment Reporting Information [Line Items] |  |  |  |
Revenues | $ 207 | $ 269 | $ 833 | $ 716
Expenses | 92 | 67 | 412 | 305
Equity in Earnings (Losses) of Investees | 20 | 18 | 76 | 47
Less: Provision (benefit) for income taxes | 21 | 44 | 92 | 88
Less: Noncontrolling interests | 9 | 5 | 21 | 12
Net Income (Loss) Attributable to AGL | 105 | 171 | 384 | 358
Subtotal |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues |  |  |  | 673
Expenses |  |  |  | 305
Equity in Earnings (Losses) of Investees |  |  |  | 47
Less: Provision (benefit) for income taxes |  |  |  | 80
Less: Noncontrolling interests |  |  |  | 12
Net Income (Loss) Attributable to AGL |  |  |  | 323
Realized gains (losses) on investments |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | (10) | 0 | (32) | 2
Net Income (Loss) Attributable to AGL | (10) | 0 | (32) | 2
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 1 |  | 61 | 11
Net Income (Loss) Attributable to AGL | 1 | (2) | (2) | 11
Fair value gains (losses) on CCS |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 8 | (3) | 9 | (12)
Net Income (Loss) Attributable to AGL | 8 | (3) | 9 | (12)
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | (22) | 54 | 82 | 42
Net Income (Loss) Attributable to AGL | (22) | 54 | 82 | 42
Tax effect |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Less: Provision (benefit) for income taxes | (4) | 8 | 9 | 8
Net Income (Loss) Attributable to AGL | 4 | (8) | (9) | (8)
Subtotal |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 230 | 218 | 713 |
Expenses | 92 | 65 | 349 |
Equity in Earnings (Losses) of Investees | 20 | 18 | 76 |
Less: Provision (benefit) for income taxes | 25 | 36 | 83 |
Less: Noncontrolling interests | 9 | 5 | 21 |
Net Income (Loss) Attributable to AGL | 124 | 130 | 336 |
Operating Segments |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 214 | 206 | 673 | 632
Expenses | 55 | 30 | 237 | 189
Equity in Earnings (Losses) of Investees | 16 | 32 | 60 | 85
Less: Provision (benefit) for income taxes | 27 | 42 | 88 | 96
Less: Noncontrolling interests | 0 | 0 | 0 | 0
Net Income (Loss) Attributable to AGL | 148 | 166 | 408 | 432
Operating Segments | Insurance |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 206 | 204 | 644 | 622
Expenses | 51 | 28 | 220 | 183
Equity in Earnings (Losses) of Investees | 16 | 28 | 48 | 83
Less: Provision (benefit) for income taxes | 26 | 42 | 83 | 95
Less: Noncontrolling interests | 0 | 0 | 0 | 0
Net Income (Loss) Attributable to AGL | 145 | 162 | 389 | 427
Operating Segments | Asset Management |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 8 | 2 | 29 | 10
Expenses | 4 | 2 | 17 | 6
Equity in Earnings (Losses) of Investees | 0 | 4 | 12 | 2
Less: Provision (benefit) for income taxes | 1 | 0 | 5 | 1
Less: Noncontrolling interests | 0 | 0 | 0 | 0
Net Income (Loss) Attributable to AGL | 3 | 4 | 19 | 5
Corporate division |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 3 | 4 | 11 | 13
Expenses | 38 | 37 | 117 | 128
Equity in Earnings (Losses) of Investees | 9 | 0 | 28 | 0
Less: Provision (benefit) for income taxes | (2) | (4) | (5) | (14)
Less: Noncontrolling interests | 0 | 0 | 0 | 0
Net Income (Loss) Attributable to AGL | (24) | (29) | (73) | (101)
Reconciling items: |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Expenses |  | 2 | 63 |
Intersegment Eliminations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 13 | 8 | 29 | 28
Expenses | (1) | (2) | (5) | (12)
Equity in Earnings (Losses) of Investees | (5) | (14) | (12) | (38)
Less: Provision (benefit) for income taxes | 0 | (2) | 0 | (2)
Less: Noncontrolling interests | 9 | 5 | 21 | 12
Net Income (Loss) Attributable to AGL | 0 | (7) | 1 | (8)
Intersegment Eliminations | Insurance |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 2 | 2 | 7 | 7
Intersegment Eliminations | Asset Management |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | $ 2 | $ 1 | $ 5 | $ 2

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