Reporting Segments - Impacts of Tax Legislation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	$ 521	$ 1,308
Tax Legislation expense (benefit)	(29)	(506)
Total income tax expense	492	802	$ 877
Property-Liability
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	576	1,253
Tax Legislation expense (benefit)	5	65
Total income tax expense	581	1,318	806
Service Businesses
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	(24)	(59)
Tax Legislation expense (benefit)	4	(134)
Total income tax expense	(20)	(193)	0
Allstate Life
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	57	108
Tax Legislation expense (benefit)	16	(332)
Total income tax expense	73	(224)	91
Allstate Benefits
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	30	52
Tax Legislation expense (benefit)	0	(51)
Total income tax expense	30	1	51
Allstate Annuities
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	3	124
Tax Legislation expense (benefit)	(69)	(182)
Total income tax expense	(66)	(58)	36
Corporate and Other
Segment Reporting Information
Income tax expense (benefit) before Tax Legislation	(121)	(170)
Tax Legislation expense (benefit)	15	128
Total income tax expense	$ (106)	$ (42)	$ (107)