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, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 245	$ 283
Expenses	125	165
Equity in Earnings (Losses) of Investees	24	2
Less: Provision (benefit) for income taxes	31	23
Less: Noncontrolling interests	4	16
Net Income (Loss) Attributable to AGL	109	81
Subtotal
Segment Reporting Information [Line Items]
Revenues	251	268
Expenses	127	165
Equity in Earnings (Losses) of Investees	24	2
Less: Provision (benefit) for income taxes	31	21
Less: Noncontrolling interests	4	16
Net Income (Loss) Attributable to AGL	113	68
Operating Segments
Segment Reporting Information [Line Items]
Revenues	230	231
Expenses	85	121
Equity in Earnings (Losses) of Investees	41	30
Less: Provision (benefit) for income taxes	36	24
Less: Noncontrolling interests	0	0
Net Income (Loss) Attributable to AGL	150	116
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Revenues	229	190
Expenses	85	79
Equity in Earnings (Losses) of Investees	40	30
Less: Provision (benefit) for income taxes	35	24
Less: Noncontrolling interests	0	0
Net Income (Loss) Attributable to AGL	149	117
Operating Segments | Asset Management
Segment Reporting Information [Line Items]
Revenues	1	41
Expenses	0	42
Equity in Earnings (Losses) of Investees	1	0
Less: Provision (benefit) for income taxes	1	0
Less: Noncontrolling interests	0	0
Net Income (Loss) Attributable to AGL	1	(1)
Corporate division
Segment Reporting Information [Line Items]
Revenues	5	2
Expenses	47	48
Equity in Earnings (Losses) of Investees	0	0
Less: Provision (benefit) for income taxes	(5)	(2)
Less: Noncontrolling interests	0	0
Net Income (Loss) Attributable to AGL	(37)	(44)
Other
Segment Reporting Information [Line Items]
Revenues	16	35
Expenses	(5)	(4)
Equity in Earnings (Losses) of Investees	(17)	(28)
Less: Provision (benefit) for income taxes	0	(1)
Less: Noncontrolling interests	4	16
Net Income (Loss) Attributable to AGL	0	(4)
Reconciling items:
Segment Reporting Information [Line Items]
Expenses	(2)
Reconciling items: | Realized gains (losses) on investments
Segment Reporting Information [Line Items]
Revenues	8	(2)
Net Income (Loss) Attributable to AGL	8	(2)
Reconciling items: | Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives
Segment Reporting Information [Line Items]
Revenues	8	13
Net Income (Loss) Attributable to AGL	10	13
Reconciling items: | Fair value gains (losses) on CCS
Segment Reporting Information [Line Items]
Revenues	(10)	(16)
Net Income (Loss) Attributable to AGL	(10)	(16)
Reconciling items: | Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves
Segment Reporting Information [Line Items]
Revenues	(12)	20
Net Income (Loss) Attributable to AGL	$ (12)	20
Reconciling items: | Tax effect
Segment Reporting Information [Line Items]
Less: Provision (benefit) for income taxes		(2)
Net Income (Loss) Attributable to AGL		$ 2