Quarterly Operating Results (Unaudited) (Details Textual) - USD ($) $ in Millions			3 Months Ended								12 Months Ended
		Dec. 24, 2015	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Operating Results (Unaudited) [Line Items]
Adverse prior year development in the property and transportation sub-segment			$ 5	$ (55)	$ 10	$ 7	$ (10)	$ (13)	$ (14)	$ 31	$ (33)	$ (6)
Other income											243	122	$ 108
Property and Casualty Insurance [Member]
Quarterly Operating Results (Unaudited) [Line Items]
Special charges to increase asbestos and environmental reserves				67				24
Former Railroad and Manufacturing Operations [Member]
Quarterly Operating Results (Unaudited) [Line Items]
Special charges to increase asbestos and environmental reserves				$ 12				$ 6
Specialty Property and transportation [Member]
Quarterly Operating Results (Unaudited) [Line Items]
Adverse prior year development in the property and transportation sub-segment									$ (22)
Run-off long-term care insurance business [Member]
Quarterly Operating Results (Unaudited) [Line Items]
Realized loss on subsidiaries		$ (166)	(4)			$ (162)					(166)
Property and Casualty Insurance [Member]
Quarterly Operating Results (Unaudited) [Line Items]
Other income	[1]										$ 78	$ 9	$ 15
Property and Casualty Insurance [Member] | Real Estate Investment [Member]
Quarterly Operating Results (Unaudited) [Line Items]
Other income			$ 15		$ 51

[1] Includes pretax income of $51 million (before noncontrolling interest) from the sale of the Le Pavillon Hotel in the second quarter of 2015 and $15 million from the sale of an apartment property in the fourth quarter of 2015.