Share-based compensation (Rollforward Of Company's Restricted Stock) (Details) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock
Number of Restricted Stock [Roll Forward]
Number of unvested restricted stock, beginning of period	5,805,126	3,489,169	3,837,097
Number of restricted stock, granted	1,707,094	1,622,065	1,417,965
Number of restricted stock, vested and issued	(2,646,084)	(2,592,622)	(1,341,358)
Number of restricted stock, forfeited	(156,694)	(420,125)	(424,535)
Number of unvested restricted stock, end of period	4,709,422	5,805,126	3,489,169
Weighted-Average Grant-Day Fair Value [Roll Forward]
Weighted average grant-day fair value of unvested restricted stock outstanding, beginning of period (US$ per share)	$ 109.39	$ 97.01	$ 83.60
Weighted average grant-day fair value of restricted stock, granted (US$ per share)	139.18	118.70	114.37
Weighted average grant-day fair value of restricted stock, vested and issued (US$ per share)	107.73	100.87	80.05
Weighted average grant-day fair value of restricted stock, forfeited (US$ per share)	114.54	109.42	87.36
Weighted average grant-day fair value of unvested restricted stock outstanding, end of period (US$ per share)	$ 121.16	$ 109.39	$ 97.01
Performance Shares
Number of Restricted Stock [Roll Forward]
Number of unvested restricted stock, beginning of period	931,169	595,210	378,690
Number of restricted stock, granted	267,282	517,507	326,860
Number of restricted stock, vested and issued	(222,954)	(181,548)	(110,340)
Number of restricted stock, forfeited	0	0	0
Number of unvested restricted stock, end of period	975,497	931,169	595,210
Weighted-Average Grant-Day Fair Value [Roll Forward]
Weighted average grant-day fair value of unvested restricted stock outstanding, beginning of period (US$ per share)	$ 111.17	$ 101.73	$ 90.87
Weighted average grant-day fair value of restricted stock, granted (US$ per share)	138.90	118.96	113.29
Weighted average grant-day fair value of restricted stock, vested and issued (US$ per share)	113.30	102.43	98.70
Weighted average grant-day fair value of restricted stock, forfeited (US$ per share)	0.00	0.00	0.00
Weighted average grant-day fair value of unvested restricted stock outstanding, end of period (US$ per share)	$ 118.28	$ 111.17	$ 101.73
The Chubb Corporation [Member] \| Restricted stock
Number of Restricted Stock [Roll Forward]
Number of restricted stock, granted		3,706,639
Weighted-Average Grant-Day Fair Value [Roll Forward]
Weighted average grant-day fair value of restricted stock, granted (US$ per share)		$ 111.02
The Chubb Corporation [Member] \| Performance Shares
Number of Restricted Stock [Roll Forward]
Number of restricted stock, granted		0
Weighted-Average Grant-Day Fair Value [Roll Forward]
Weighted average grant-day fair value of restricted stock, granted (US$ per share)		$ 0.00

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(3)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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+ References

No definition available.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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