Summary of Significant Accounting Policies - Schedule of Deferred Policy Acquisition Costs Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Beginning balance	$ 5,773	$ 5,940	$ 5,442
Acquisition costs deferred	8,784	8,393	7,776
Amortization charged to income	(8,384)	(8,022)	(7,246)
Experience adjustment	(5)	(17)	(32)
Reclassified to assets held for sale	(5)	(521)	0
Ending balance	6,163	5,773	5,940
Allstate Protection
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Beginning balance		2,378
Ending balance			2,378
Protection Services
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Beginning balance		3,022
Ending balance			3,022
Allstate Health and Benefits
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Beginning balance		497
Ending balance	0		497
All other
Movement Analysis of Deferred Policy Acquisition Costs and Present Value of Future Profits [Roll Forward]
Beginning balance	63	43
Ending balance	$ 86	$ 63	$ 43