Debt (Schedule of debt instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Short term debt
8.375%, face amount of $70, due August 15, 2012		$ 70
Other debt	13	13
Total short term debt	13	83
Long term debt
Total long term debt	2,557	2,525
Total debt	2,570	2,608
Senior notes 5.850%, face amount $549, due December 15, 2014
Long term debt
Senior notes, noncurrent	548	548
Senior notes 6.500%, face amount of $350, due August 15, 2016
Long term debt
Senior notes, noncurrent	348	348
Senior notes 6.950%, face amount $150, due January 15, 2018
Long term debt
Senior notes, noncurrent	149	149
Senior notes 7.350%, face amount $350, due November 15, 2019
Long term debt
Senior notes, noncurrent	348	348
Senior notes 5.875%, face amount $500, due August 15, 2020
Long term debt
Senior notes, noncurrent	496	495
Senior notes 5.750%, face amount $400, due August 15, 2021
Long term debt
Senior notes, noncurrent	397	396
Debenture of CNAF
Long term debt
Debenture of CNAF, 7.250%, face amount of $243, due November 15, 2023	241	241
Subordinated variable rate debt
Long term debt
Subordinated variable rate debt of Hardy, face amount of $30, due September 15, 2036	$ 30

Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments, excluding current portion.

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