Claim and Claim Adjustment Expense Reserves Net prior year claim and allocated claim adjustment expense reserve development for International segment (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (132)	$ (175)	$ (282)	$ (187)
International [Member]
Medical Professional Liability	(2)	(8)	(3)	(8)
Other Professional Liability	(1)	(11)	16	(16)
Liability	(2)	(5)	(21)	(12)
Property & Marine	(9)	(5)	(16)	(19)
Other	(1)	(5)	(10)	9
Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development, excluding Life & Group	$ (15)	$ (34)	$ (34)	$ (46)

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

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

No definition available.

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Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development, Liability

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Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development, Other Professional Liability

No definition available.

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Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development, Property & Marine

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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