Share-based compensation (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended								12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Stock options	Dec. 31, 2012 Restricted stock	Dec. 31, 2011 Restricted stock	Dec. 31, 2010 Restricted stock	Dec. 31, 2009 Restricted stock	Dec. 31, 2012 Restricted Stock Units (RSUs)	Dec. 31, 2011 Restricted Stock Units (RSUs)	Dec. 31, 2010 Restricted Stock Units (RSUs)	Dec. 31, 2012 ACE Limited 2004 Long-Term Incentive Plan Restricted stock	Dec. 31, 2012 Common shares ACE Limited 2004 Long-Term Incentive Plan	May 31, 2012 Common shares ACE Limited 2004 Long-Term Incentive Plan	Dec. 31, 2004 Common shares ACE Limited 2004 Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares authorized for issuance under plan															30,600,000
Common shares available for future issuance under plan													6,593,991
Vesting period of award				3 years								4 years
Cmmon shares authorized for issuance under the ESPP														1,500,000
Common shares remaining as available for issuance under the ESPP													1,491,053
Unrecognized compensation expense related to the unvested share-based awards	$ 119
Weighted-average expected recognition period for the unrecognized compensation expense	1 year
Stock option term in years				10 years
Weighted average remaining contractual term for stock options outstanding	6 years 2 months 6 days
Weighted-average remaining contractual term for stock options exercisable	4 years 9 months 12 days
Cash received from exercise of stock options	95
Restricted stock awards granted to non-management directors	25,669	32,660	36,248
Restricted stock units awarded to employees and officers of ACE and subsidiaries during period					1,589,178	1,808,745	2,461,076		262,549	261,214	326,091
Weighted average grant-day fair value of restricted stock units granted to employees and officers of the company (US$ per share)					$ 73.46	$ 60.01	$ 51.09		$ 73.41	$ 62.85	$ 50.36
Number of unvested restricted stock units outstanding					4,254,847	4,851,490	5,305,732	4,873,429	637,085
Number of deferred restricted stock units									196,431
Amounts paid during period by employees for the purchase of shares under the ESPP	$ 13	$ 12	$ 10
Number of shares purchased during period by employees pursuant to the provisions of the ESPP	198,244	205,812	240,979