Reserves for Future Policy Benefits and Unpaid Losses and Loss Adjustment Expenses Level 4 Prior Accident Years Reserve Development (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	$ 228	$ 192	$ (4)
Auto liability [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	25	144	(25)
Homeowners [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	(7)	(6)	(32)
Professional Liability [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	(17)	(29)	40
Package Business [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	3	2	(20)
Workers Compensation [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	(7)	(2)	78
Workers Compensation NY Section 25A [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	0	80	0
General liability [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	(25)	(75)	(87)
Fidelity and Surety [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	8	(8)	(9)
Commercial property [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	2	(7)	(8)
Net asbestos reserves [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	212	130	48
Net environmental reserves [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	30	12	10
Uncollectible reinsurance [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	0	(25)	0
Change in workers compensation discount, including accretion [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	30	30	52
Catastrophes [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	(45)	(63)	(66)
Other reserve re-estimates [Member]
Prior accident years reserve development
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease)	$ 19	$ 9	$ 15