Reporting Segments - Performance data and tax items (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information
Amortization of DAC	$ 4,784	$ 4,550	$ 4,364
Income tax expense	802	877	1,111
Allstate Protection
Segment Reporting Information
Amortization of DAC	4,205	4,053	3,933
Service Businesses
Segment Reporting Information
Amortization of DAC	296	214	169
Income tax expense	(193)	0	2
Allstate Life
Segment Reporting Information
Amortization of DAC	134	131	133
Income tax expense	(224)	91	108
Allstate Benefits
Segment Reporting Information
Amortization of DAC	142	145	124
Income tax expense	1	51	55
Allstate Annuities
Segment Reporting Information
Amortization of DAC	7	7	5
Income tax expense	(58)	36	188
Property-Liability
Segment Reporting Information
Income tax expense	1,318	806	867
Corporate and Other
Segment Reporting Information
Income tax expense	$ (42)	$ (107)	$ (109)