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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
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 300	$ 177
Expenses	196	171
Equity in Earnings (Losses) of Investees	(11)	9
Less: Provision (benefit) for income taxes	18	0
Less: Noncontrolling interests	9	4
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	3	(3)
Fair value gains (losses) on committed capital securities	1	(19)
Total consolidated	66	11
Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	300	177
Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	196	171
Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	(11)	9
Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	18	0
Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	9	4
Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	66	11
Operating Segments
Segment Reporting Information [Line Items]
Revenues	317	199
Expenses	161	135
Equity in Earnings (Losses) of Investees	(1)	19
Less: Provision (benefit) for income taxes	22	11
Less: Noncontrolling interests	0	0
Segment adjusted operating income (loss)	133	72
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Revenues	278	179
Expenses	122	106
Equity in Earnings (Losses) of Investees	(1)	19
Less: Provision (benefit) for income taxes	22	13
Less: Noncontrolling interests	0	0
Segment adjusted operating income (loss)	133	79
Operating Segments | Asset Management
Segment Reporting Information [Line Items]
Revenues	39	20
Expenses	39	29
Equity in Earnings (Losses) of Investees	0	0
Less: Provision (benefit) for income taxes	0	(2)
Less: Noncontrolling interests	0	0
Segment adjusted operating income (loss)	0	(7)
Corporate division
Segment Reporting Information [Line Items]
Revenues	1	0
Expenses	34	32
Equity in Earnings (Losses) of Investees	0	0
Less: Provision (benefit) for income taxes	0	(3)
Less: Noncontrolling interests	0	0
Segment adjusted operating income (loss)	(33)	(29)
Other
Segment Reporting Information [Line Items]
Revenues	14	21
Expenses	5	7
Equity in Earnings (Losses) of Investees	(10)	(10)
Less: Provision (benefit) for income taxes	0	0
Less: Noncontrolling interests	9	4
Segment adjusted operating income (loss)	(10)	0
Realized gains (losses) on investments | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	3	(3)
Realized gains (losses) on investments | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	0	0
Realized gains (losses) on investments | Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	0	0
Realized gains (losses) on investments | Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	0	0
Realized gains (losses) on investments | Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	0	0
Realized gains (losses) on investments | Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	3	(3)
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives	(7)	(22)
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives	(4)	(3)
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives | Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives	0	0
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives | Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives	0	0
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives | Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives	0	0
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives | Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives	(3)	(19)
Fair value gains (losses) on CCS | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	1	(19)
Fair value gains (losses) on CCS | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	0	0
Fair value gains (losses) on CCS | Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	0	0
Fair value gains (losses) on CCS | Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	0	0
Fair value gains (losses) on CCS | Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	0	0
Fair value gains (losses) on CCS | Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	1	(19)
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	(29)	1
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	0	0
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves | Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	0	0
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves | Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	0	0
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves | Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	0	0
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves | Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	(29)	1
Tax effect | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0
Tax effect | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0
Tax effect | Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0
Tax effect | Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	(4)	(8)
Tax effect | Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0
Tax effect | Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	4	8
Subtotal
Segment Reporting Information [Line Items]
Revenues	332	220
Expenses	200	174
Equity in Earnings (Losses) of Investees	(11)	9
Less: Provision (benefit) for income taxes	22	8
Less: Noncontrolling interests	9	4
Segment adjusted operating income (loss)	$ 90	$ 43

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