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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 24	$ (5)	$ 49	$ (31)
Hardy [Member]
Marine and Aviation	1	4	6	3
Non-Marine Property	3	7	1	7
Property Treaty	(2)	2	(4)	2
Specialty	(2)	(1)	(3)	(1)
Commutations			10
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group		$ 12	$ 10	$ 11