General - Schedule of condensed consolidated statements of operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Revenues
Total revenues	$ 13,979	$ 12,219	$ 27,765	$ 24,555
Costs and expenses
Accident, health and other policy benefits	258	265	523	533
Amortization of deferred policy acquisition costs	1,789	1,618	3,533	3,226
Total costs and expenses	15,727	13,530	29,919	25,065
Loss from operations before income tax expense	(1,748)	(1,311)	(2,154)	(510)
Income tax benefit	(373)	(289)	(458)	(138)
Net loss	(1,375)	(1,022)	(1,696)	(372)
Net loss attributable to Allstate	(1,352)	(1,013)	(1,672)	(353)
Net loss applicable to common shareholders, Basic	(1,389)	(1,040)	(1,735)	(406)
Net loss applicable to common shareholders, Diluted	$ (1,389)	$ (1,040)	$ (1,735)	$ (406)
Earnings per common share:
Net loss applicable to common shareholders per common share - Basic (in dollars per share)	$ (5.29)	$ (3.80)	$ (6.59)	$ (1.47)
Net loss applicable to common shareholders per common share - Diluted (in dollars per share)	$ (5.29)	$ (3.80)	$ (6.59)	$ (1.47)
As reported
Revenues
Total revenues		$ 12,220		$ 24,557
Costs and expenses
Accident, health and other policy benefits		269		538
Amortization of deferred policy acquisition costs		1,619		3,231
Total costs and expenses		13,535		25,075
Loss from operations before income tax expense		(1,315)		(518)
Income tax benefit		(291)		(140)
Net loss		(1,024)		(378)
Net loss attributable to Allstate		(1,015)		(359)
Net loss applicable to common shareholders, Basic		(1,042)		(412)
Net loss applicable to common shareholders, Diluted		$ (1,042)		$ (412)
Earnings per common share:
Net loss applicable to common shareholders per common share - Basic (in dollars per share)		$ (3.81)		$ (1.49)
Net loss applicable to common shareholders per common share - Diluted (in dollars per share)		$ (3.81)		$ (1.49)
Impact of change
Revenues
Total revenues		$ (1)		$ (2)
Costs and expenses
Accident, health and other policy benefits		(4)		(5)
Amortization of deferred policy acquisition costs		(1)		(5)
Total costs and expenses		(5)		(10)
Loss from operations before income tax expense		4		8
Income tax benefit		2		2
Net loss		2		6
Net loss attributable to Allstate		2		6
Net loss applicable to common shareholders, Basic		2		6
Net loss applicable to common shareholders, Diluted		$ 2		$ 6
Earnings per common share:
Net loss applicable to common shareholders per common share - Basic (in dollars per share)		$ 0.01		$ 0.02
Net loss applicable to common shareholders per common share - Diluted (in dollars per share)		$ 0.01		$ 0.02
Accident and health insurance premiums and contract charges
Revenues
Insurance premiums and contract charges	$ 453	$ 465	$ 916	$ 933
Accident and health insurance premiums and contract charges | As reported
Revenues
Insurance premiums and contract charges		466		935
Accident and health insurance premiums and contract charges | Impact of change
Revenues
Insurance premiums and contract charges		$ (1)		$ (2)