Debt (Schedule Of Debt Outstanding) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Short-term debt	$ 1,251	$ 1,300
Long-term debt	3,360	3,358
Trust preferred securities	309	309
Revolving Credit Facility [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Short-term debt		300
Reverse Repurchase Agreement [Member]
Debt Instrument [Line Items]
Short-term debt	1,251	1,000
Debt Due Date 2014 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	500	500
Debt Due Date 2015 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	449	447
Debt Due Date 2015 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	699	699
Debt Due Date 2017 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	500	500
Debt Due Date 2018 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	300	300
Debt Due Date 2019 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	500	500
Debt Due Date 2029 [Member] | Debentures [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	100	100
Debt Due Date 2036 [Member] | Senior Notes [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Long-term debt	299	299
Debt Due Date 2020 [Member] | Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt	13	13
Debt Due Date 2030 [Member] | Capital Securities [Member] | Debt Issuer ACE INA [Member]
Debt Instrument [Line Items]
Trust preferred securities	$ 309	$ 309