Claim and Claim Adjustment Expense Reserves Net prior year claim and allocated claim adjustment expense reserve development for Hardy segment (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (26)	$ (81)	$ 23	$ (112)
Hardy [Member]
Marine and Aviation	2		8	3
Non-Marine Property	2	1	3	8
Property Treaty	(1)	(5)	(5)	(3)
Specialty	(3)	(2)	(6)	(3)
Commutations			10
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group		$ (6)	$ 10	$ 5