Postretirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Jan. 14, 2016
Defined Benefit Plan Disclosure [Line Items]
Contributions During Current Period	$ 27
Expected Contribution For Remainder of Year	38
Service Cost		$ 2
Interest Cost		5
Expected Return on Plan Assets		(7)
Amortization of Actuarial (Gain) Loss		1
Net Periodic Benefit Cost		1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	22
Interest Cost	35
Expected Return on Plan Assets	(47)
Amortization of Actuarial (Gain) Loss	1
Net Periodic Benefit Cost	$ 11
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] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of Compensation Increase	4.00%
Expected Long-term Rate of Return on Plan Assets Assumption	7.00%
Discount Rate	4.28%
Service Cost	$ 17	0
Interest Cost	27	0
Expected Return on Plan Assets	(37)	0
Amortization of Actuarial (Gain) Loss	0	0
Net Periodic Benefit Cost	$ 7	0
Pension Plan [Member] | U.S. [Member] | 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)
Pension Plan [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of Compensation Increase	3.40%		3.09%
Expected Long-term Rate of Return on Plan Assets Assumption	4.90%		4.81%
Discount Rate	3.74%		3.51%
Service Cost	$ 5	2
Interest Cost	8	5
Expected Return on Plan Assets	(10)	(7)
Amortization of Actuarial (Gain) Loss	1	1
Net Periodic Benefit Cost	4	$ 1
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)
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	2
Interest Cost	5
Expected Return on Plan Assets	(2)
Amortization of Actuarial (Gain) Loss	0
Net Periodic Benefit Cost	$ 5
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] | U.S. [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected Long-term Rate of Return on Plan Assets Assumption	7.00%
Discount Rate	4.41%
Service Cost	$ 2
Interest Cost	5
Expected Return on Plan Assets	(2)
Amortization of Actuarial (Gain) Loss	0
Net Periodic Benefit Cost	$ 5
Other Postretirement Benefit Plan [Member] | U.S. [Member] | 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)
Other Postretirement Benefit Plan [Member] | Non-US [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.30%
Service Cost	$ 0
Interest Cost	0
Expected Return on Plan Assets	0
Amortization of Actuarial (Gain) Loss	0
Net Periodic Benefit Cost	$ 0
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)