Reserve for Property-Liability Insurance Claims and Claims Expense (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	$ (84)	$ (121)	$ (665)
Total auto
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	(238)	(237)	(365)
Catastrophes
Increase (decrease) in claims and claims expense
Losses from catastrophes, net of recoveries	1,990	1,250	2,350
Reserve reestimates | Other personal lines
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	13	(21)	(30)
Reserve reestimates | Discontinued Lines and Coverages
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	112	142	51
Catastrophe loss reestimates
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	43	88	410
Catastrophe loss reestimates | Homeowners
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves			(321)
Non-catastrophes loss reestimates | Homeowners
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	$ 29	$ (5)