General - Schedule of consolidated statements of operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues
Total revenues	$ 13,786	$ 12,336
Costs and expenses
Accident, health and other policy benefits	265	268
Amortization of deferred policy acquisition costs	1,744	1,608
Total costs and expenses	14,192	11,535
Income from operations before income tax expense	(406)	801
Income tax (benefit) expense	(85)	151
Net (loss) income	(321)	650
Net income attributable to Allstate	(320)	660
Net (loss) income applicable to common shareholders	(346)	634
Net income applicable to common shareholders	$ (346)	$ 634
Earnings per common share:
Net income applicable to common shareholders per common share - Basic (in dollars per share)	$ (1.31)	$ 2.28
Net income applicable to common shareholders per common share - Diluted (in dollars per share)	$ (1.31)	$ 2.25
As reported
Revenues
Total revenues		$ 12,337
Costs and expenses
Accident, health and other policy benefits		269
Amortization of deferred policy acquisition costs		1,612
Total costs and expenses		11,540
Income from operations before income tax expense		797
Income tax (benefit) expense		151
Net (loss) income		646
Net income attributable to Allstate		656
Net (loss) income applicable to common shareholders		630
Net income applicable to common shareholders		$ 630
Earnings per common share:
Net income applicable to common shareholders per common share - Basic (in dollars per share)		$ 2.27
Net income applicable to common shareholders per common share - Diluted (in dollars per share)		$ 2.24
Impact of change
Revenues
Total revenues		$ (1)
Costs and expenses
Accident, health and other policy benefits		(1)
Amortization of deferred policy acquisition costs		(4)
Total costs and expenses		(5)
Income from operations before income tax expense		4
Income tax (benefit) expense		0
Net (loss) income		4
Net income attributable to Allstate		4
Net (loss) income applicable to common shareholders		4
Net income applicable to common shareholders		$ 4
Earnings per common share:
Net income applicable to common shareholders per common share - Basic (in dollars per share)		$ 0.01
Net income applicable to common shareholders per common share - Diluted (in dollars per share)		$ 0.01
Accident and health insurance premiums and contract charges
Revenues
Insurance premiums and contract charges	$ 463	$ 468
Accident and health insurance premiums and contract charges | As reported
Revenues
Insurance premiums and contract charges		469
Accident and health insurance premiums and contract charges | Impact of change
Revenues
Insurance premiums and contract charges		$ (1)