Share-based compensation (Rollforward Of Company's Restricted Stock) (Details) - $ / shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted stock
Number of Restricted Stock [Roll Forward]
Number of unvested restricted stock, beginning of period	3,294,010	3,294,849	4,709,442
Number of restricted stock, granted	1,425,667	1,492,900	1,326,979
Number of restricted stock, vested and issued	(1,304,308)	(1,292,864)	(2,545,090)
Number of restricted stock, forfeited	(152,074)	(200,875)	(196,482)
Number of unvested restricted stock, end of period	3,263,295	3,294,010	3,294,849
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)	$ 136.20	$ 134.17	$ 121.16
Weighted average grant-day fair value of restricted stock, granted (US$ per share)	148.56	134.38	142.76
Weighted average grant-day fair value of restricted stock, vested and issued (US$ per share)	134.02	129.18	114.83
Weighted average grant-day fair value of restricted stock, forfeited (US$ per share)	140.72	135.98	131.06
Weighted average grant-day fair value of unvested restricted stock outstanding, end of period (US$ per share)	$ 142.32	$ 136.20	$ 134.17
Performance Shares
Number of Restricted Stock [Roll Forward]
Number of unvested restricted stock, beginning of period	876,212	911,230	975,497
Number of restricted stock, granted	186,291	212,059	180,065
Number of restricted stock, vested and issued	(490,185)	(196,640)	(244,332)
Number of restricted stock, forfeited	0	(50,437)	0
Number of unvested restricted stock, end of period	572,318	876,212	911,230
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)	$ 131.16	$ 127.27	$ 118.28
Weighted average grant-day fair value of restricted stock, granted (US$ per share)	151.14	133.90	143.07
Weighted average grant-day fair value of restricted stock, vested and issued (US$ per share)	125.66	115.62	103.03
Weighted average grant-day fair value of restricted stock, forfeited (US$ per share)	0	132.36	0
Weighted average grant-day fair value of unvested restricted stock outstanding, end of period (US$ per share)	$ 142.38	$ 131.16	$ 127.27

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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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.

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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).

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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).

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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.

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

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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

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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.

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