Claim and Claim Adjustment Expense Reserves (Net prior year claim and allocated claim adjustment expense reserve development for Commercial segment) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (210)	$ (21)	$ (118)
Commercial [Member]
Commercial Auto	(22)	31	18
General Liability	(33)	45	64
Workers' Compensation	80	139	91
Property and Other	(40)	(39)	(51)
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (15)	$ 176	$ 122

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

No definition available.

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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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