Segment Information - Reconciliation of Net Income (Loss) Attributable to AGL to Segment Adjusted Operating Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Revenues	$ 360	$ 90	$ 643	$ 390
Expenses	221	112	386	308
Equity in Earnings (Losses) of Investees	5	0	7	(11)
Less: Provision (benefit) for income taxes	18	3	41	21
Less: Noncontrolling interests	1	22	17	31
Net Income (Loss) Attributable to AGL	125	(47)	206	19
Subtotal
Segment Reporting Information [Line Items]
Revenues	253	175	521	507
Expenses	222	112	387	312
Equity in Earnings (Losses) of Investees	5	0	7	(11)
Less: Provision (benefit) for income taxes	(1)	11	20	33
Less: Noncontrolling interests	1	22	17	31
Net Income (Loss) Attributable to AGL	36	30	104	120
Operating Segments
Segment Reporting Information [Line Items]
Revenues	254	167	485	484
Expenses	143	69	264	230
Equity in Earnings (Losses) of Investees	5	(34)	35	(35)
Less: Provision (benefit) for income taxes	12	9	36	31
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	104	55	220	188
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Revenues	224	139	414	417
Expenses	110	41	189	163
Equity in Earnings (Losses) of Investees	5	(34)	35	(35)
Less: Provision (benefit) for income taxes	13	9	37	31
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	106	55	223	188
Operating Segments | Asset Management
Segment Reporting Information [Line Items]
Revenues	30	28	71	67
Expenses	33	28	75	67
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	(1)	0	(1)	0
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	(2)	0	(3)	0
Corporate division
Segment Reporting Information [Line Items]
Revenues	2	1	4	2
Expenses	60	36	108	70
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	(8)	0	(10)	0
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	(50)	(35)	(94)	(68)
Other
Segment Reporting Information [Line Items]
Revenues	(3)	7	32	21
Expenses	19	7	15	12
Equity in Earnings (Losses) of Investees	0	34	(28)	24
Less: Provision (benefit) for income taxes	(5)	2	(6)	2
Less: Noncontrolling interests	1	22	17	31
Net Income (Loss) Attributable to AGL	(18)	10	(22)	0
Reconciling items: | Realized gains (losses) on investments
Segment Reporting Information [Line Items]
Revenues	(9)	(28)	(11)	(25)
Expenses	0	0	0	0
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	0	0	0	0
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	(9)	(28)	(11)	(25)
Reconciling items: | Non-credit impairment-related unrealized fair value gains (losses) on credit derivatives
Segment Reporting Information [Line Items]
Revenues	89	6	102	(1)
Expenses	(1)	0	(1)	(4)
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	0	0	0	0
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	90	6	103	3
Reconciling items: | Fair value gains (losses) on CCS
Segment Reporting Information [Line Items]
Revenues	1	10	(15)	11
Expenses	0	0	0	0
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	0	0	0	0
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	1	10	(15)	11
Reconciling items: | Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves
Segment Reporting Information [Line Items]
Revenues	26	(73)	46	(102)
Expenses	0	0	0	0
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	0	0	0	0
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	26	(73)	46	(102)
Reconciling items: | Tax effect
Segment Reporting Information [Line Items]
Revenues	0	0	0	0
Expenses	0	0	0	0
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	(19)	8	(21)	12
Less: Noncontrolling interests	0	0	0	0
Net Income (Loss) Attributable to AGL	$ 19	$ (8)	$ 21	$ (12)