Debt (Schedule of debt instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Long term debt	$ 2,559us-gaap_LongTermDebtNoncurrent	$ 2,011us-gaap_LongTermDebtNoncurrent
Total debt	2,559us-gaap_LongTermDebt
Debt, Long-term and Short-term, Combined Amount		2,560
Senior notes 6.500%, face amount of $350, due August 15, 2016
Long term debt	349	349
Senior notes 6.950%, face amount $150, due January 15, 2018
Long term debt	150	149
Senior notes 7.350%, face amount $350, due November 15, 2019
Long term debt	348	348
Senior notes 5.875%, face amount $500, due August 15, 2020
Long term debt	497	497
Senior notes 5.750%, face amount $400, due August 15, 2021
Long term debt	397	397
Senior Notes, 3.950%, face amount of $550, due May 15, 2024
Long term debt	547
Debenture of CNAF, 7.250%, face amount of $243, due November 15, 2023
Long term debt	241	241
Subordinated variable rate debt of Hardy, face amount of $30, due September 15, 2036
Long term debt	30	30
Senior notes 5.850%, face amount $549, due December 15, 2014
Short term debt		$ 549

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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