Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for Specialty segment) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (21)	$ (118)	$ (205)
Specialty [Member]
Medical Professional Liability	39	(27)	(34)
Other Professional Liability and Management Liability	(87)	(73)	19
Surety	(82)	(74)	(63)
Warranty	(2)	(3)	(5)
Other	(4)	(19)	(10)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (136)	$ (196)	$ (93)