General - Schedule of condensed consolidated statements of comprehensive income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net (loss) income	$ (321)	$ 650
Changes in:
Unrealized net capital gains and losses	682	(1,594)
Discount rate for reserve for future policy benefits	(9)	95
Other comprehensive income (loss), after-tax	719	(1,514)
Comprehensive income (loss)	398	(864)
Comprehensive income (loss) attributable to Allstate	$ 394	(842)
As reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net (loss) income		646
Changes in:
Unrealized net capital gains and losses		(1,593)
Discount rate for reserve for future policy benefits		0
Other comprehensive income (loss), after-tax		(1,608)
Comprehensive income (loss)		(962)
Comprehensive income (loss) attributable to Allstate		(940)
Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net (loss) income		4
Changes in:
Unrealized net capital gains and losses		(1)
Discount rate for reserve for future policy benefits		95
Other comprehensive income (loss), after-tax		94
Comprehensive income (loss)		98
Comprehensive income (loss) attributable to Allstate		$ 98