Guarantees and Contingent Liabilities (Details)				9 Months Ended	12 Months Ended	21 Months Ended
	Sep. 02, 2016 claim	May 20, 2016 plaintiff	Jun. 17, 2015 plaintiff	Sep. 30, 2016 USD ($) claim defense	Dec. 31, 2001 employee	Sep. 30, 2016 USD ($) plaintiff	Apr. 08, 2016 adjuster	Dec. 31, 2015 USD ($)	Aug. 19, 2015 opinion
Guarantees:
Limitations or indemnifications of reinsurance agreements				$ 0		$ 0
Proceedings:
Number of class action cases | claim	2			2
Loss contingency, pending claims, adjusters omitted, number | adjuster							50
Opinions, number | opinion									3
Loss contingency, number of plaintiffs		499	10		32	459
Number of former employee agents plaintiffs seek benefits for | employee					6,300
Number of defenses | defense				2
Reserves for asbestos claims				$ 936,000,000		$ 936,000,000		$ 960,000,000
Reinsurance recoverables for asbestos claims				463,000,000		463,000,000		458,000,000
Reserves for environmental claims				190,000,000		190,000,000		179,000,000
Reinsurance recoverables for environmental claims				$ 43,000,000		$ 43,000,000		$ 43,000,000
Percentage of net asbestos and environmental reserves that were for incurred but not reported estimated losses				59.00%		59.00%		57.00%
Minimum
Proceedings:
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued				$ 0
Maximum
Proceedings:
Loss contingencies, reasonably possible pretax loss exposure in excess of the amount accrued				875,000,000
Residual guarantee
Guarantees:
Potential leased automobiles residual value				$ 45,000,000		$ 45,000,000
Guarantee obligations term, low end of range				1 year
Guarantee obligations term, high end of range				4 years
Adjuster Opted Out [Member]
Proceedings:
Loss contingency, pending claims, number | adjuster							11
Fair Labor Standards Act [Member]
Proceedings:
Loss contingency, pending claims, number | adjuster							105
New York Labor Law [Member]
Proceedings:
Loss contingency, pending claims, number | adjuster							137
Against Allstate
Proceedings:
Opinions, number | opinion									2
In Favor of Allstate
Proceedings:
Opinions, number | opinion									1
Signed Releases Knowingly and Voluntarily | Judicial Ruling
Proceedings:
Loss contingency, number of plaintiffs | plaintiff			2
Did Not Sign Releases Knowingly and Voluntarily | Judicial Ruling
Proceedings:
Loss contingency, number of plaintiffs | plaintiff			8