Fair Value of Assets and Liabilities - Schedule of Valuation Changes Included in Net Income and OCI for Level 3 Assets and Liabilities Held (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	$ 22	$ 37	$ 55
Fair Value Recurring Basis Unobservable Input Reconciliation Liability Gain Loss Statement Of Income Extensible List Not Disclosed Flag	Total included in net income	Total included in net income	Total included in net income
Total included in net income	$ 22	$ 37	$ 55
Total included in net income	22	37	55
Changes in unrealized net capital gains and losses reported in OCI	$ (1)	$ 3	$ (4)
Net investment income
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair Value, Asset, Recurring Basis, Still Held, Unrealized 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
Total included in net income	$ (8)	$ (1)	$ 14
Net gains (losses) on investments and derivatives
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair Value, Asset, Recurring Basis, Still Held, Unrealized 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
Total included in net income	$ 14	$ 23	$ 3
Operating costs and expenses
Gains (losses) included in net income for Level 3 assets and liabilities:
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Operating costs and expenses	Operating costs and expenses	Operating costs and expenses
Total included in net income	$ 16	$ 15	$ 38
Municipal
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	(2)	0	0
Changes in unrealized net capital gains and losses reported in OCI	0	0	1
Corporate - public
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	1	0	0
Changes in unrealized net capital gains and losses reported in OCI	0	1	(5)
Corporate - privately placed
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	(6)	(12)	1
Changes in unrealized net capital gains and losses reported in OCI	(1)	2	0
Fixed income securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	(7)	(12)	1
Equity securities
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	13	35	14
Other investments
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	0	(1)	2
Other assets
Gains (losses) included in net income for Level 3 assets and liabilities:
Total recurring Level 3 assets	$ 16	$ 15	$ 38