Debt (Schedule of Debt Outstanding) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Short-term debt	$ 1,401	$ 1,251
Long-term debt	3,360	3,360
Trust preferred securities	309	309
Senior Notes
Debt Instrument [Line Items]
Long-term debt	3,360	3,360
Senior Notes | ACE INA senior notes due 2014
Debt Instrument [Line Items]
Long-term debt	500	500
Senior Notes | ACE INA senior notes due 2015
Debt Instrument [Line Items]
Long-term debt	449	449
Senior Notes | ACE INA senior notes due 2015
Debt Instrument [Line Items]
Long-term debt	699	699
Senior Notes | ACE INA senior notes due 2017
Debt Instrument [Line Items]
Long-term debt	500	500
Senior Notes | ACE INA senior notes due 2018
Debt Instrument [Line Items]
Long-term debt	300	300
Senior Notes | ACE INA senior notes due 2019
Debt Instrument [Line Items]
Long-term debt	500	500
Senior Notes | ACE INA senior notes due 2036
Debt Instrument [Line Items]
Long-term debt	299	299
Senior Notes | Other
Debt Instrument [Line Items]
Long-term debt	13	13
Senior secured debentures | ACE INA debentures due 2029
Debt Instrument [Line Items]
Long-term debt	100	100
Trust Preferred Securities | ACE INA capital securities due 2030
Debt Instrument [Line Items]
Trust preferred securities	309	309
Reverse repurchase agreements
Debt Instrument [Line Items]
Short-term debt	$ 1,401	$ 1,251