Fair Value of Assets and Liabilities - Schedule of Rollforward of Level 3 Assets and Liabilities Held at Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Assets
Balance at beginning of period	$ 676	$ 618	$ 565
Total gains (losses) included in: Net income	23	40	76
Total gains (losses) included in: OCI	(1)	2	(2)
Transfers into Level 3	0	16	2
Transfers out of Level 3	0	0	(28)
Transfers (to) from held for sale	0
Purchases	191	122	155
Sales	(76)	(101)	(121)
Issues	0	0	0
Settlements	(11)	(21)	(29)
Balance at end of period	$ 802	$ 676	$ 618
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Allstate Protection and Run-off Property-Liability net investment income, Net gains (losses) on investments and derivatives	Allstate Protection and Run-off Property-Liability net investment income, Net gains (losses) on investments and derivatives	Allstate Protection and Run-off Property-Liability net investment income, Net gains (losses) on investments and derivatives
Net investment income
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Allstate Protection and Run-off Property-Liability net investment income	Allstate Protection and Run-off Property-Liability net investment income	Allstate Protection and Run-off Property-Liability net investment income
Gain (loss) included in earnings	$ (8)	$ (1)	$ 15
Net gains (losses) on investments and derivatives
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net gains (losses) on investments and derivatives	Net gains (losses) on investments and derivatives	Net gains (losses) on investments and derivatives
Gain (loss) included in earnings	$ 15	$ 26	$ 23
Operating costs and expenses
Total Level 3 gains (losses) included in net income
Fair Value, Asset (Liability), Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses
Gain (loss) included in earnings	$ 16	$ 15	$ 38
Municipal
Assets
Balance at beginning of period	11	21	18
Total gains (losses) included in: Net income	(2)	3	0
Total gains (losses) included in: OCI	1	(1)	1
Transfers into Level 3	0	0	2
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	0
Purchases	0	0	2
Sales	(5)	(10)	0
Issues	0	0	0
Settlements	(3)	(2)	(2)
Balance at end of period	2	11	21
Corporate - public
Assets
Balance at beginning of period	26	69	20
Total gains (losses) included in: Net income	1	(1)	0
Total gains (losses) included in: OCI	0	2	(5)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	(7)
Purchases	16	0	66
Sales	(14)	(44)	(10)
Issues	0	0	0
Settlements	0	0	(2)
Balance at end of period	22	26	69
Corporate - privately placed
Assets
Balance at beginning of period	58	55	66
Total gains (losses) included in: Net income	(6)	(12)	19
Total gains (losses) included in: OCI	(2)	1	2
Transfers into Level 3	0	16	0
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	0
Purchases	64	1	34
Sales	(2)	(3)	(65)
Issues	0	0	0
Settlements	(2)	0	(1)
Balance at end of period	110	58	55
ABS
Assets
Balance at beginning of period	58	28	40
Total gains (losses) included in: Net income	0	0	1
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	(28)
Transfers (to) from held for sale	0
Purchases	59	31	17
Sales	0	0	0
Issues	0	0	0
Settlements	(3)	(1)	(2)
Balance at end of period	114	58	28
Fixed income securities
Assets
Balance at beginning of period	153	173	144
Total gains (losses) included in: Net income	(7)	(10)	20
Total gains (losses) included in: OCI	(1)	2	(2)
Transfers into Level 3	0	16	2
Transfers out of Level 3	0	0	(28)
Transfers (to) from held for sale	(7)
Purchases	139	32	119
Sales	(21)	(57)	(75)
Issues	0	0	0
Settlements	(8)	(3)	(7)
Balance at end of period	248	153	173
Equity securities
Assets
Balance at beginning of period	402	333	349
Total gains (losses) included in: Net income	8	36	16
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	0
Purchases	25	77	13
Sales	(28)	(44)	(45)
Issues	0	0	0
Settlements	0	0	0
Balance at end of period	407	402	333
Short-term investments
Assets
Balance at beginning of period	1	6	5
Total gains (losses) included in: Net income	0	0	0
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	0
Purchases	27	13	23
Sales	(20)	0	0
Issues	0	0	0
Settlements	(3)	(18)	(22)
Balance at end of period	5	1	6
Other investments
Assets
Balance at beginning of period	2	3	2
Total gains (losses) included in: Net income	6	(1)	2
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	0
Purchases	0	0	0
Sales	(7)	0	(1)
Issues	0	0	0
Settlements	0	0	0
Balance at end of period	1	2	3
Other assets
Assets
Balance at beginning of period	118	103	65
Total gains (losses) included in: Net income	16	15	38
Total gains (losses) included in: OCI	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Transfers (to) from held for sale	0
Purchases	0	0	0
Sales	0	0	0
Issues	0	0	0
Settlements	0	0	0
Balance at end of period	134	118	$ 103
Assets held for sale
Assets
Balance at beginning of period	0
Total gains (losses) included in: Net income	0
Total gains (losses) included in: OCI	0
Transfers into Level 3	0
Transfers out of Level 3	0
Transfers (to) from held for sale	7
Purchases	0
Sales	0
Issues	0
Settlements	0
Balance at end of period	$ 7	$ 0