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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Revenues	$ 90	$ 196	$ 390	$ 373
Expenses	112	105	308	276
Equity in Earnings (Losses) of Investees	0	34	(11)	43
Less: Provision (benefit) for income taxes	3	23	21	23
Less: Noncontrolling interests	22	4	31	8
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	(28)	4	(25)	1
Fair value gains (losses) on committed capital securities	10	(6)	11	(25)
Total consolidated	(47)	98	19	109
Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	90	196	390	373
Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	112	105	308	276
Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	0	34	(11)	43
Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	3	23	21	23
Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	22	4	31	8
Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Total consolidated	(47)	98	19	109
Operating Segments
Segment Reporting Information [Line Items]
Revenues	167	203	484	402
Expenses	69	71	230	206
Equity in Earnings (Losses) of Investees	(34)	48	(35)	67
Less: Provision (benefit) for income taxes	9	30	31	41
Less: Noncontrolling interests	0	0	0	0
Segment adjusted operating income (loss)	55	150	188	222
Operating Segments | Insurance
Segment Reporting Information [Line Items]
Revenues	139	182	417	361
Expenses	41	47	163	153
Equity in Earnings (Losses) of Investees	(34)	48	(35)	67
Less: Provision (benefit) for income taxes	9	31	31	44
Less: Noncontrolling interests	0	0	0	0
Segment adjusted operating income (loss)	55	152	188	231
Operating Segments | Asset Management
Segment Reporting Information [Line Items]
Revenues	28	21	67	41
Expenses	28	24	67	53
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	0	(1)	0	(3)
Less: Noncontrolling interests	0	0	0	0
Segment adjusted operating income (loss)	0	(2)	0	(9)
Corporate division
Segment Reporting Information [Line Items]
Revenues	1	0	2	0
Expenses	36	36	70	68
Equity in Earnings (Losses) of Investees	0	0	0	0
Less: Provision (benefit) for income taxes	0	(2)	0	(5)
Less: Noncontrolling interests	0	0	0	0
Segment adjusted operating income (loss)	(35)	(34)	(68)	(63)
Subtotal
Segment Reporting Information [Line Items]
Revenues	175	230	507	450
Expenses	112	111	312	285
Equity in Earnings (Losses) of Investees	0	34	(11)	43
Less: Provision (benefit) for income taxes	11	29	33	37
Less: Noncontrolling interests	22	4	31	8
Segment adjusted operating income (loss)	30	120	120	163
Other
Segment Reporting Information [Line Items]
Revenues	7	27	21	48
Expenses	7	4	12	11
Equity in Earnings (Losses) of Investees	34	(14)	24	(24)
Less: Provision (benefit) for income taxes	2	1	2	1
Less: Noncontrolling interests	22	4	31	8
Segment adjusted operating income (loss)	10	4	0	4
Realized gains (losses) on investments | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	(28)	4	(25)	1
Realized gains (losses) on investments | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Realized gains (losses) on investments	0	0	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	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	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	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	(28)	4	(25)	1
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	6	(37)	(1)	(59)
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	0	(6)	(4)	(9)
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	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	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	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	6	(31)	3	(50)
Fair value gains (losses) on CCS | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Fair value gains (losses) on committed capital securities	10	(6)	11	(25)
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	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	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	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	10	(6)	11	(25)
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	(73)	5	(102)	6
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	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	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	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	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	(73)	5	(102)	6
Tax effect | Revenues
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0	0	0
Tax effect | Expenses
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0	0	0
Tax effect | Equity in Earnings (Losses) of Investees
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0	0	0
Tax effect | Provision (Benefit) for Income Taxes
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	(8)	(6)	(12)	(14)
Tax effect | Nonredeemable Noncontrolling Interests
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	0	0	0	0
Tax effect | Net Income (Loss) Attributable to AGL
Segment Reporting, Other Significant Reconciling Item, Consolidated [Abstract]
Tax effect	$ 8	$ 6	$ 12	$ 14