Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Components of net periodic cost
Percentage related to domestic plan	90.00%
Percentage related to domestic plan and former final average pay formula	79.00%
Maximum annual medical cost inflation after retirement for Company's share of retiree medical benefits cost for non Medicare-eligible retirees (as a percent)	5.00%
Components of net periodic cost
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Amortization of Prior Service Cost (Credit), Statement of Income or Comprehensive Income [Extensible Enumeration]	Allstate Protection and Run-off Property-Liability net investment income, Operating costs and expenses, Claims and claims expense, Restructuring and related charges
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Interest Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Allstate Protection and Run-off Property-Liability net investment income, Operating costs and expenses, Claims and claims expense, Restructuring and related charges
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Expected Return (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Allstate Protection and Run-off Property-Liability net investment income, Operating costs and expenses, Claims and claims expense, Restructuring and related charges
Pension benefits
Components of net periodic cost
Accumulated benefit obligation	$ 4,360	$ 4,480
Company's Pension Plans with an ABO in excess of plan assets
Company's pension plans with ABO in excess of plan assets, aggregate projected benefit obligation	74	4,270
Company's pension plans with ABO in excess of plan assets, aggregate accumulated benefit obligation	72	4,180
Company's pension plans with ABO in excess of plan assets, aggregate fair value of plan assets	0	4,090
Defined benefit plans' accrued benefit costs related to certain unfunded and non-qualified plans	74	78
Components of net periodic cost
Service cost, refund	$ 38	$ 38
Postretirement benefits
Defined benefit plan, assumed health care cost trend rates
Weighted average health care cost trend rate (as a percent)	6.80%
Ultimate health care cost trend rate in 2035 and thereafter (as a percent)	4.50%