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	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (175)	$ (26)	$ (187)	$ 23
Commercial [Member]
Commercial Auto	0	13	7	52
General Liability	3	44	8	76
Workers' Compensation	(1)	25	22	75
Property and Other	(13)	(11)	(37)	(24)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (11)	$ 71	$ 0	$ 179

Net prior year claim and allocated claim adjustment expense reserve development, Commercial Auto

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Net prior year claim and allocated claim adjustment expense reserve development, General Liability

No definition available.

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Net prior year claim and allocated claim adjustment expense reserve development, Property and Other

No definition available.

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Net prior year claim and allocated claim adjustment expense reserve development, Workers' Compensation

No definition available.

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Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group

No definition available.

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