Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior Notes	Dec. 31, 2011 Senior Notes	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2014	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2014	Jun. 30, 2004 Senior Notes ACE INA senior notes due 2014	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2015	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2015	May 31, 2008 Senior Notes ACE INA senior notes due 2015	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2015	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2015	Nov. 30, 2010 Senior Notes ACE INA senior notes due 2015	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2017	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2017	Feb. 28, 2007 Senior Notes ACE INA senior notes due 2017	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2018	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2018	Feb. 29, 2008 Senior Notes ACE INA senior notes due 2018	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2019	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2019	Jun. 30, 2009 Senior Notes ACE INA senior notes due 2019	Dec. 31, 2012 Senior Notes ACE INA senior notes due 2036	Dec. 31, 2011 Senior Notes ACE INA senior notes due 2036	May 31, 2006 Senior Notes ACE INA senior notes due 2036	Dec. 31, 2012 Senior Notes Pennsylvania Industrial Development Authority (PIDA)	Aug. 30, 2005 Senior Notes Pennsylvania Industrial Development Authority (PIDA)	Dec. 31, 2012 Senior Notes City Of Philadelphia Urban Development Action Grant	Dec. 30, 1999 Senior Notes City Of Philadelphia Urban Development Action Grant	Dec. 31, 2012 Senior secured debentures ACE INA debentures due 2029	Dec. 31, 2011 Senior secured debentures ACE INA debentures due 2029	Aug. 31, 1999 Senior secured debentures ACE INA debentures due 2029	Dec. 31, 2012 Trust Preferred Securities ACE INA capital securities due 2030	Mar. 31, 2000 Trust Preferred Securities ACE INA capital securities due 2030	Dec. 31, 2012 Reverse repurchase agreements	Dec. 31, 2011 Reverse repurchase agreements
Debt Instrument [Line Items]
Short-term debt	$ 1,401	$ 1,251																																	$ 1,401	$ 1,251
Weighted average interest rate on short-term debt																																			0.40%
Debt issued							500			450			700			500			300			500			300		10		8			100	309	300
Long-term debt stated interest rate							5.875%			5.60%			2.60%			5.70%			5.80%			5.90%			6.70%		2.75%		7.10%			8.875%	9.70%	9.70%
Additional percentage on 'make-whole' premium							0.20%			0.35%			0.20%			0.20%			0.35%			0.40%			0.20%
Current amount of long-term debt outstanding	3,360	3,360	3,360	3,360	500	500		449	449		699	699		500	500		300	300		500	500		299	299		6		7		100	100
ACE Capital Trust II common securities purchased																																		$ 9.2
Percent of principal amount of Subordinated Debentures																																	100.00%