Reserves for Future Policy Benefits and Unpaid Losses and Loss Adjustment Expenses ((Favorable) Unfavorable Prior Accident Years) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Prior accident years reserve development
Prior years	$ 192	$ (4)	$ 367
Auto liability [Member]
Prior accident years reserve development
Prior years	144	(25)	(97)
Homeowners [Member]
Prior accident years reserve development
Prior years	(6)	(32)	(1)
Professional Liability [Member]
Prior accident years reserve development
Prior years	(29)	40	29
Package Business [Member]
Prior accident years reserve development
Prior years	2	(20)	(76)
Workers' Compensation [Member]
Prior accident years reserve development
Prior years	(2)	78	171
Workers Compensation NY Section 25A [Member]
Prior accident years reserve development
Prior years	80	0	0
General liability [Member]
Prior accident years reserve development
Prior years	(75)	(87)	(40)
Fidelity and Surety [Member]
Prior accident years reserve development
Prior years	(8)	(9)	(7)
Commercial property [Member]
Prior accident years reserve development
Prior years	(7)	(8)	(4)
Net asbestos reserves [Member]
Prior accident years reserve development
Prior years	130	48	294
Net environmental reserves [Member]
Prior accident years reserve development
Prior years	12	10	26
Uncollectible reinsurance [Member]
Prior accident years reserve development
Prior years	(25)	0	0
Change in workers compensation discount, including accretion [Member]
Prior accident years reserve development
Prior years	30	52	38
Catastrophes [Member]
Prior accident years reserve development
Prior years	(63)	(66)	37
Other reserve re-estimates [Member]
Prior accident years reserve development
Prior years	$ 9	$ 15	$ (3)