Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for Commercial segment) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (5)	$ 24	$ (12)	$ 49
Commercial [Member]
Commercial Auto	7	19	7	39
General Liability	1	32	5	32
Workers' Compensation	24	39	23	50
Property and Other	(16)	0	(24)	(13)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 16	$ 90	$ 11	$ 108