Reserve for Property-Liability Insurance Claims and Claims Expense (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	$ 17	$ 81	$ 84
Auto
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	(155)	30	(238)
Catastrophes
Increase (decrease) in claims and claims expense
Losses from catastrophes, net of recoveries	2,570	1,720	1,990
Non-catastrophes loss reestimates | Homeowners
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	(24)	(24)
Reserve reestimates | Other personal lines
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	57	22	13
Reserve reestimates | Discontinued Lines and Coverages
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	105	53	112
Catastrophe loss reestimates
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves	$ 6	$ (15)	43
Catastrophe loss reestimates | Homeowners
Increase (decrease) in claims and claims expense
Net increase (decrease) to reserves			$ 29