Postretirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Jan. 14, 2016
Defined Benefit Plan Disclosure [Line Items]
Contributions During Current Period	$ 24		$ 156
Expected Contribution For Remainder of Year			8
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	26	$ 2	72	$ 5
Interest Cost	34	5	104	15
Expected Return on Plan Assets	(52)	(7)	(151)	(21)
Amortization of Actuarial (Gain) Loss	0	0	2	2
Curtailments	(4)		(4)
Settlements	(1)		(1)
Net Periodic Benefit Cost	3	0	22	1
Pension Plan [Member] | The Chubb Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets						$ 2,788
Projected Benefit Obligation						(3,525)
Funded Status of Plan						(737)
Pension Plan [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	6	2	15	5
Interest Cost	8	5	24	15
Expected Return on Plan Assets	(10)	(7)	(30)	(21)
Amortization of Actuarial (Gain) Loss	0	0	2	2
Curtailments	0		0
Settlements	0		0
Net Periodic Benefit Cost	4	0	$ 11	1
Discount Rate			3.74%		3.51%
Rate of Compensation Increase			3.40%		3.09%
Expected Long-term Rate of Return on Plan Assets Assumption			4.90%		4.81%
Pension Plan [Member] | Non-US [Member] | The Chubb Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets						315
Projected Benefit Obligation						(372)
Funded Status of Plan						(57)
Pension Plan [Member] | U.S.
Defined Benefit Plan Disclosure [Line Items]
Service Cost	20	0	$ 57	0
Interest Cost	26	0	80	0
Expected Return on Plan Assets	(42)	0	(121)	0
Amortization of Actuarial (Gain) Loss	0	0	0	0
Curtailments	(4)		(4)
Settlements	(1)		(1)
Net Periodic Benefit Cost	(1)	$ 0	$ 11	$ 0
Discount Rate			4.28%
Rate of Compensation Increase			4.00%
Expected Long-term Rate of Return on Plan Assets Assumption			7.00%
Pension Plan [Member] | U.S. | The Chubb Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets						2,473
Projected Benefit Obligation						(3,153)
Funded Status of Plan						(680)
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	4		$ 9
Interest Cost	4		13
Expected Return on Plan Assets	(3)		(7)
Amortization of Actuarial (Gain) Loss			0
Curtailments	0		0
Settlements	0		0
Net Periodic Benefit Cost	5		15
Other Postretirement Benefit Plan [Member] | The Chubb Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets						138
Projected Benefit Obligation						(506)
Funded Status of Plan						(368)
Other Postretirement Benefit Plan [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0		1
Interest Cost	0		0
Expected Return on Plan Assets	0		0
Amortization of Actuarial (Gain) Loss	0		0
Curtailments	0		0
Settlements	0		0
Net Periodic Benefit Cost	0		$ 1
Discount Rate			4.30%
Other Postretirement Benefit Plan [Member] | Non-US [Member] | The Chubb Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets						0
Projected Benefit Obligation						(15)
Funded Status of Plan						(15)
Other Postretirement Benefit Plan [Member] | U.S.
Defined Benefit Plan Disclosure [Line Items]
Service Cost	4		$ 8
Interest Cost	4		13
Expected Return on Plan Assets	(3)		(7)
Amortization of Actuarial (Gain) Loss	0		0
Curtailments	0		0
Settlements	0		0
Net Periodic Benefit Cost	$ 5		$ 14
Discount Rate			4.41%
Expected Long-term Rate of Return on Plan Assets Assumption			7.00%
Other Postretirement Benefit Plan [Member] | U.S. | The Chubb Corporation [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets						138
Projected Benefit Obligation						(491)
Funded Status of Plan						$ (353)