Reportable Segments - Financial performance (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
Net investment income	$ 562	$ 974	$ 1,156	$ 1,682
Net gains (losses) on investments and derivatives	(733)	287	(1,000)	713
Pension and other postretirement remeasurement gains (losses)	(259)	134	(12)	444
Income (loss) from discontinued operations	0	493	0	(3,670)
Income tax benefit (expense) from discontinued operations	0	(297)	0	73
Total from discontinued operations	0	196	0	(3,597)
Less: Net income (loss) attributable to noncontrolling interest	(9)	6	(19)	0
Net (loss) income applicable to common shareholders	(1,042)	1,595	(412)	187
Segment Reconciling Items
Segment Reporting Information
Adjusted net income	(189)	970	156	1,701
Net investment income	506	931	1,064	1,604
Net gains (losses) on investments and derivatives	(733)	287	(1,000)	713
Pension and other postretirement remeasurement gains (losses)	(259)	134	(12)	444
Business combination expenses and amortization of purchased intangibles	(28)	(34)	(57)	(90)
Business combination fair value adjustment	0	6	0	6
Gain (loss) on disposition of operations	27	0	11	0
Income tax benefit (expense) on reconciling items	298	(354)	150	(976)
Allstate Protection \| Operating Segments
Segment Reporting Information
Underwriting income (loss)	(861)	431	(579)	2,091
Run-off Property-Liability \| Operating Segments
Segment Reporting Information
Underwriting income (loss)	(3)	(2)	(5)	(5)
Property-Liability
Segment Reporting Information
Net investment income	506	931	1,064	1,604
Net gains (losses) on investments and derivatives	(662)	265	(865)	669
Less: Net income (loss) attributable to noncontrolling interest	(10)	6	(20)	0
Property-Liability \| Operating Segments
Segment Reporting Information
Underwriting income (loss)	(864)	429	(584)	2,086
Protection Services \| Operating Segments
Segment Reporting Information
Adjusted net income	43	56	96	105
Allstate Health and Benefits
Segment Reporting Information
Net investment income	16	19	33	38
Net gains (losses) on investments and derivatives	(12)	4	(19)	6
Allstate Health and Benefits \| Operating Segments
Segment Reporting Information
Adjusted net income	65	62	118	127
Corporate and Other \| Operating Segments
Segment Reporting Information
Adjusted net income	(107)	(112)	(218)	(235)
Net investment income	28	12	38	18
Net gains (losses) on investments and derivatives	$ (29)	$ 12	$ (73)	$ 22

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