Share-based compensation (Rollforward Of Company's Stock Options) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Options, Weighted-Average Fair Value and Total Intrinsic Value [Abstract]
Weighted-average fair value of stock options granted (US$ per share)	$ 22.97	$ 21.52	$ 18.49
Total intrinsic value of options exercised	$ 111	$ 99	$ 72
Total intrinsic value of options outstanding	490
Total intrinsic value of options exercisable, December 31, 2015	$ 424
Number of Options [Roll Forward]
Number of option outstanding, beginning of period	10,180,720	9,853,496	9,623,986
Number of options granted	2,079,522	1,929,616	1,892,641
Number of options exercised	(1,632,629)	(1,728,949)	(1,457,580)
Number of options forfeited	(194,297)	(213,339)	(205,551)
Number of option outstanding, end of period	10,433,316	10,180,720	9,853,496
Number of options exercisable, December 31, 2015	6,675,491
Weighted-Average Exercise Price [Roll Forward]
Weighted-average exercise price of options outstanding, beginning of period (US$ oer share)	$ 87.29	$ 78.40	$ 69.06
Weighted-average exercise price of options granted (US$ per share)	139.00	118.39	114.78
Weighted-average exercise price of options exercised (US$ per share)	73.53	66.65	60.88
Weighted average exercise price of options forfeited (US$ per share)	119.44	110.01	100.25
Weighted-average exercise price of options outstanding, end of period (US$ oer share	99.20	87.29	$ 78.40
Weighted average exercise price of options exercisable, December 31, 2015 (US$ per share)	$ 82.59
The Chubb Corporation [Member]
Options, Weighted-Average Fair Value and Total Intrinsic Value [Abstract]
Weighted-average fair value of stock options granted (US$ per share)		$ 36.07
Number of Options [Roll Forward]
Number of options granted		339,896
Weighted-Average Exercise Price [Roll Forward]
Weighted-average exercise price of options granted (US$ per share)		$ 77.83