Condensed Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 1,631	$ 1,250	$ 244	$ 1,799
Changes in:
Unrealized net capital gains and losses	484	2,072	(1,016)	715
Unrealized foreign currency translation adjustments	(3)	9	31	(30)
Unamortized pension and other postretirement prior service credit	(14)	(11)	(29)	(7)
Other comprehensive income (loss), after-tax	467	2,070	(1,014)	678
Comprehensive income (loss)	2,098	3,320	(770)	2,477
Less: Comprehensive income (loss) attributable to noncontrolling interest	5	0	(1)	0
Comprehensive income (loss) applicable to Allstate	$ 2,093	$ 3,320	$ (769)	$ 2,477