General - Schedule of Condensed Consolidated Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Revenues
Total revenues	$ 14,497	$ 13,208	$ 42,262	$ 37,763
Costs and expenses
Accident, health and other policy benefits	262	252	785	785
Amortization of deferred policy acquisition costs	1,841	1,683	5,374	4,909
Total costs and expenses	14,518	14,118	44,437	39,183
Loss from operations before income tax expense	(21)	(910)	(2,175)	(1,420)
Income tax benefit	(17)	(236)	(475)	(374)
Net loss	(4)	(674)	(1,700)	(1,046)
Net loss attributable to Allstate	(5)	(659)	(1,677)	(1,012)
Net loss applicable to common shareholders, basic	(41)	(685)	(1,776)	(1,091)
Net loss applicable to common shareholders, diluted	$ (41)	$ (685)	$ (1,776)	$ (1,091)
Earnings per common share:
Net income (loss) applicable to common shareholders per common share - Basic (in dollars per share)	$ (0.16)	$ (2.55)	$ (6.76)	$ (3.99)
Net income (loss) applicable to common shareholders per common share - Diluted (in dollars per share)	$ (0.16)	$ (2.55)	$ (6.76)	$ (3.99)
As reported
Revenues
Total revenues		$ 13,208		$ 37,765
Costs and expenses
Accident, health and other policy benefits		263		801
Amortization of deferred policy acquisition costs		1,682		4,913
Total costs and expenses		14,128		39,203
Loss from operations before income tax expense		(920)		(1,438)
Income tax benefit		(237)		(377)
Net loss		(683)		(1,061)
Net loss attributable to Allstate		(668)		(1,027)
Net loss applicable to common shareholders, basic		(694)		(1,106)
Net loss applicable to common shareholders, diluted		$ (694)		$ (1,106)
Earnings per common share:
Net income (loss) applicable to common shareholders per common share - Basic (in dollars per share)		$ (2.58)		$ (4.04)
Net income (loss) applicable to common shareholders per common share - Diluted (in dollars per share)		$ (2.58)		$ (4.04)
Impact of change
Revenues
Total revenues		$ 0		$ (2)
Costs and expenses
Accident, health and other policy benefits		(11)		(16)
Amortization of deferred policy acquisition costs		1		(4)
Total costs and expenses		(10)		(20)
Loss from operations before income tax expense		10		18
Income tax benefit		1		3
Net loss		9		15
Net loss attributable to Allstate		9		15
Net loss applicable to common shareholders, basic		9		15
Net loss applicable to common shareholders, diluted		$ 9		$ 15
Earnings per common share:
Net income (loss) applicable to common shareholders per common share - Basic (in dollars per share)		$ 0.03		$ 0.05
Net income (loss) applicable to common shareholders per common share - Diluted (in dollars per share)		$ 0.03		$ 0.05
Accident and health insurance premiums and contract charges
Revenues
Accident and health insurance premiums and contract charges	$ 463	$ 463	$ 1,379	$ 1,396
Accident and health insurance premiums and contract charges | As reported
Revenues
Accident and health insurance premiums and contract charges		463		1,398
Accident and health insurance premiums and contract charges | Impact of change
Revenues
Accident and health insurance premiums and contract charges		$ 0		$ (2)