Unpaid losses and loss expenses (Narrative) (Details) (USD $)	12 Months Ended				12 Months Ended																																			12 Months Ended						12 Months Ended								12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2004	Dec. 31, 2013 Insurance - Overseas General	Dec. 31, 2012 Insurance - Overseas General	Dec. 31, 2011 Insurance - Overseas General	Dec. 31, 2013 Global Reinsurance	Dec. 31, 2012 Global Reinsurance	Dec. 31, 2011 Global Reinsurance	Dec. 31, 2013 Long tail Insurance - Overseas General	Dec. 31, 2012 Long tail Insurance - Overseas General	Dec. 31, 2013 Long tail Global Reinsurance	Dec. 31, 2013 Long tail Excess casualty business Insurance - Overseas General	Dec. 31, 2013 Long tail Excess casualty business 2009 and prior Insurance - Overseas General	Dec. 31, 2012 Long tail Excess casualty business 2009 and prior Insurance - Overseas General	Dec. 31, 2013 Long tail Excess casualty business 2008 and prior Insurance - Overseas General	Dec. 31, 2012 Long tail Excess casualty business 2008 and prior Insurance - Overseas General	Dec. 31, 2013 Long tail Medical risk operations 2009 and prior Global Reinsurance	Dec. 31, 2012 Long tail Medical risk operations 2008 and prior Global Reinsurance	Dec. 31, 2013 Long tail Financial solutions business Insurance - Overseas General	Dec. 31, 2013 Long tail Financial solutions business 2009 and prior Insurance - Overseas General	Dec. 31, 2013 Long tail Financial solutions business 2012 Insurance - Overseas General	Dec. 31, 2013 Long tail Non Medical Professional Liability [Member] 2008 and prior Global Reinsurance	Dec. 31, 2013 Short tail Insurance - Overseas General	Dec. 31, 2013 Short tail Other lines Insurance - North American Agriculture	Dec. 31, 2012 Short tail Other lines Insurance - North American Agriculture	Dec. 31, 2011 Short tail Other lines Insurance - North American Agriculture	Dec. 31, 2013 Short tail Property portfolios Insurance - Overseas General	Dec. 31, 2012 Short tail Property portfolios 2009 to 2010 Insurance - Overseas General	Dec. 31, 2013 Short tail Property portfolios 2008 to 2009 Insurance - Overseas General	Dec. 31, 2013 Short tail Property portfolios 2009 and prior Global Reinsurance	Dec. 31, 2012 Short tail Property portfolios 2009 and prior Global Reinsurance	Dec. 31, 2013 Short tail Property portfolios 2008 and prior Insurance - Overseas General	Dec. 31, 2013 Short tail Aviation lines [Domain] 2009 and prior Insurance - Overseas General	Dec. 31, 2013 Insurance - Overseas General	Dec. 31, 2011 Insurance - Overseas General	Dec. 31, 2011 Global Reinsurance	Dec. 31, 2013 Penn Millers	Dec. 31, 2013 Brandywine	Dec. 31, 2012 Brandywine	Dec. 31, 2013 Westchester Specialty	Dec. 31, 2012 Westchester Specialty	Dec. 31, 1998 Westchester Specialty	Dec. 31, 2013 Ace Bermuda [Member]	Dec. 31, 2013 Net of NICO Coverage Brandywine	Dec. 31, 2013 Net of NICO Coverage Westchester Specialty	Dec. 31, 2013 Run Off [Member] Insurance - North American P&C	Dec. 31, 2012 Run Off [Member] Insurance - North American P&C	Dec. 31, 2011 Run Off [Member] Insurance - North American P&C	Dec. 31, 2013 Run Off [Member] Completion of reserve review Insurance - North American P&C	Dec. 31, 2012 Run Off [Member] Completion of reserve review Insurance - North American P&C	Dec. 31, 2011 Run Off [Member] Insurance - North American	Dec. 31, 2013 Active [Member] Insurance - North American P&C	Dec. 31, 2012 Active [Member] Insurance - North American P&C	Dec. 31, 2011 Active [Member] Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Directors and Officers (D&O) Portfolio 2007 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Directors and Officers (D&O) Portfolio 2008 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Excess casualty business 2007 and prior Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Excess casualty business 2007 and prior Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Medical risk operations 2007 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Medical risk operations 2007 to 2009 Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail National accounts portfolio Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail National accounts portfolio 2007 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail National accounts portfolio 2012 Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Foreign casualty Products 2009 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Other lines Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Completion of reserve review 2012 Insurance - North American P&C	Dec. 31, 2013 Active [Member] Long tail Workers Compensation [Domain] 2006 and prior Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Workers Compensation [Domain] 2006 and prior Insurance - North American P&C	Dec. 31, 2012 Active [Member] Long tail Workers Compensation [Domain] 2007 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Short tail Insurance - North American P&C	Dec. 31, 2012 Active [Member] Short tail Insurance - North American P&C	Dec. 31, 2012 Active [Member] Short tail Property and inland marine lines 2008 to 2010 Insurance - North American P&C	Dec. 31, 2013 Active [Member] Short tail Property and inland marine lines 2009 and prior Insurance - North American P&C	Dec. 31, 2013 Active [Member] Short tail Political risk lines [Domain] 2009 to 2010 Insurance - North American P&C	Dec. 31, 2012 Active [Member] Short tail Aviation lines [Domain] 2009 and prior Insurance - North American P&C	Dec. 31, 2011 Active [Member] Insurance - North American
Unpaid Losses and Loss Expenses [Line Items]
Net losses and loss expenses incurred in prior years	$ 530,000,000	$ 479,000,000	$ 556,000,000		$ 299,000,000	$ 226,000,000	$ 290,000,000	$ 84,000,000	$ 61,000,000	$ 71,000,000	$ 127,000,000	$ 121,000,000	$ 53,000,000	$ 92,000,000	$ 135,000,000	$ (29,000,000)	$ (43,000,000)	$ 150,000,000	$ 20,000,000	$ 54,000,000	$ 35,000,000	$ 63,000,000	$ (28,000,000)	$ 25,000,000	$ 172,000,000	$ 13,000,000	$ 12,000,000	$ 8,000,000	$ 104,000,000	$ 105,000,000	$ 69,000,000	$ 31,000,000	$ 29,000,000	$ 35,000,000	$ 29,000,000													$ (193,000,000)	$ (168,000,000)	$ (102,000,000)	$ (161,000,000)	$ (150,000,000)		$ 327,000,000	$ 348,000,000	$ (289,000,000)	$ 221,000,000	$ 245,000,000	$ 67,000,000	$ 72,000,000	$ 50,000,000	$ 73,000,000	$ 57,000,000	$ 63,000,000	$ 28,000,000	$ 39,000,000	$ 40,000,000	$ 25,000,000	$ 28,000,000	$ 41,000,000	$ (40,000,000)	$ (36,000,000)	$ 34,000,000	$ 106,000,000	$ 103,000,000	$ 88,000,000	$ 45,000,000	$ 29,000,000	$ 27,000,000
Prior period net unpaid reserves represented by prior period development (percent)																																					(4.20%)	(3.10%)															(0.60%)																											(1.80%)
Unallocated loss adjustment expenses due to operating expenses paid and reserved	(9,878,000,000)	(10,132,000,000)	(10,076,000,000)
A & E - change in net loss reserves																																								166,000,000	146,000,000	5,000,000	4,000,000
A & E - change in gross loss reserves																																								277,000,000	275,000,000	3,000,000	(17,000,000)
A & E - loss reserves, net - closing	1,051,000,000	1,106,000,000																																		79,000,000			3,000,000	816,000,000		146,000,000			7,000,000
A & E - incurred activity, net	171,000,000																																							158,000,000		14,000,000
NICO reinsurance protection on losses and loss expenses																																								2,500,000,000
Incurred activity	9,348,000,000	9,653,000,000	9,520,000,000																																											167,000,000	1,000,000
NICO pro-rata share of reinsurance protection (percent)																																												75.00%
NICO reinsurance protection on losses and loss expenses incurred on or before 12/31/1996, net of retenion																																												1,000,000,000
NICO retention for losses and loss expenses incurred on or before 12/31/1996																																												721,000,000
NICO remaining unused limit under the 1998 agreement																																												490,000,000
Dividend retention fund established by INA Financial Corporation	50,000,000
Required minimum balance under the dividend retention fund	50,000,000
Minimum contribution from the dividend retention fund to Century not required for XOL agreement	200,000,000
Reinsurance coverage to Century provided by ACE INA under XOL	800,000,000
Statutory surplus of century	25,000,000
Century Statutory Basis Losses Cede To X O L	232,000,000
INA Holdings contibutions to Century in exchange for a surplus note				100,000,000
Aggregate reinsurance balances ceded by active ACE companies to Century	929,000,000	958,000,000
Century's carried gross reserves (including reserves ceded by active ACE companies)	$ 2,300,000,000	$ 2,100,000,000