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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 269	$ 403	$ 716	$ 1,046
Expenses	67	219	305	605
Equity in Earnings (Losses) of Investees	18	18	47	25
Less: Provision (benefit) for income taxes	44	43	88	84
Less: Noncontrolling interests	5	2	12	19
Net Income (Loss) Attributable to AGL	171	157	358	363
Subtotal
Segment Reporting Information [Line Items]
Revenues	218	463	673	984
Expenses	65	219	305	606
Equity in Earnings (Losses) of Investees	18	18	47	25
Less: Provision (benefit) for income taxes	36	54	80	74
Less: Noncontrolling interests	5	2	12	19
Net Income (Loss) Attributable to AGL	130	206	323	310
Operating Segments
Segment Reporting Information [Line Items]
Revenues	206	208	632	693
Expenses	30	165	189	429
Equity in Earnings (Losses) of Investees	32	25	85	60
Less: Provision (benefit) for income taxes	42	9	96	45
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	166	59	432	279
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Revenues	204	208	622	622
Expenses	28	165	183	354
Equity in Earnings (Losses) of Investees	28	25	83	60
Less: Provision (benefit) for income taxes	42	9	95	46
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	162	59	427	282
Operating Segments | Asset Management
Segment Reporting Information [Line Items]
Revenues	2	0	10	71
Expenses	2	0	6	75
Equity in Earnings (Losses) of Investees	4	0	2	0
Less: Provision (benefit) for income taxes	0	0	1	(1)
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	4	0	5	(3)
Corporate division
Segment Reporting Information [Line Items]
Revenues	4	259	13	263
Expenses	37	57	128	165
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	(4)	47	(14)	37
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	(29)	155	(101)	61
Other
Segment Reporting Information [Line Items]
Revenues	8	(4)	28	28
Expenses	(2)	(3)	(12)	12
Equity in Earnings (Losses) of Investees	(14)	(7)	(38)	(35)
Less: Provision (benefit) for income taxes	(2)	(2)	(2)	(8)
Less: Noncontrolling interests	5	2	12	19
Net Income (Loss) Attributable to AGL	(7)	(8)	(8)	(30)
Reconciling items: | Realized gains (losses) on investments
Segment Reporting Information [Line Items]
Revenues		(9)	2	(20)
Net Income (Loss) Attributable to AGL		(9)	2	(20)
Reconciling items: | Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives
Segment Reporting Information [Line Items]
Revenues		6	11	108
Expenses	2			(1)
Net Income (Loss) Attributable to AGL	(2)	6	11	109
Reconciling items: | Fair value gains (losses) on CCS
Segment Reporting Information [Line Items]
Revenues	(3)	(20)	(12)	(35)
Net Income (Loss) Attributable to AGL	(3)	(20)	(12)	(35)
Reconciling items: | Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves
Segment Reporting Information [Line Items]
Revenues	54	(37)	42	9
Net Income (Loss) Attributable to AGL	54	(37)	42	9
Reconciling items: | Tax effect
Segment Reporting Information [Line Items]
Less: Provision (benefit) for income taxes	8	(11)	8	(10)
Net Income (Loss) Attributable to AGL	$ (8)	$ (11)	$ 8	$ 10