Reporting Segments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reporting Segments
Number of reportable segments	4
Period within which an unusual or infrequent item is unlikely to recur	2 years
Prior period with no similar unusual or infrequent item	2 years
Outside United States
Segment Reporting Information
Revenues from external customers generated outside the United States	$ 0	$ 0	$ 0
Allstate Protection
Segment Reporting Information
Revenues from external customers generated outside the United States	$ 1,080	$ 1,060	$ 992