Additional Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Additional Information (Textual) [Abstract]
Total rental expense	$ 65us-gaap_OperatingLeasesRentExpenseNet	$ 57us-gaap_OperatingLeasesRentExpenseNet	$ 51us-gaap_OperatingLeasesRentExpenseNet
Operating lease future minimum payments due in next year	62
Operating lease future minimum payments due in year two	59
Operating lease future minimum payments due in year three	50
Operating lease future minimum payments due in year four	42
Operating lease future minimum payments due in year five	38
Operating lease future minimum payments due after year five	174
Commitments to fund limited partnerships	370
Retirement and employee savings plan expense	30	32	27
Allowance for reinsurance recoverables [Member]
Allowance for reinsurance recoverables [Line Items]
Aggregate allowance for losses on reinsurance recoverables	25	27
Charges for possible losses on reinsurance recoverables (are less than in 2012)	4	1	1
Reinsurance recoverable write-offs	$ 6

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Represents commitments to fund credit facilities and contribute capital to certain limited partnership investments at a future date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

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The amount of costs recognized during the period for non-pension postretirement benefits, such as medical, dental and life insurance.

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Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs.

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Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively.

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