Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for Commercial 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)
Commercial [Member]
Commercial Auto	31	18	25
General Liability	45	64	(66)
Workers' Compensation	139	91	15
Property and Other	(39)	(51)	1
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ 176	$ 122	$ (25)