Postretirement benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jan. 14, 2016
Defined Benefit Plan Disclosure [Line Items]
Contributions During Current Period	$ 105		$ 132
Expected Contribution For Remainder of Year			19
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	24	$ 1	46	$ 3
Interest Cost	35	5	70	10
Expected Return on Plan Assets	(52)	(7)	(99)	(14)
Amortization of Actuarial (Gain) Loss	1	1	2	2
Net Periodic Benefit Cost	8	0	$ 19	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] | 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	20	0	$ 37	0
Interest Cost	27	0	54	0
Expected Return on Plan Assets	(42)	0	(79)	0
Amortization of Actuarial (Gain) Loss	0	0	0	0
Net Periodic Benefit Cost	5	0	$ 12	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	4	1	$ 9	3
Interest Cost	8	5	16	10
Expected Return on Plan Assets	(10)	(7)	(20)	(14)
Amortization of Actuarial (Gain) Loss	1	1	2	2
Net Periodic Benefit Cost	3	$ 0	7	$ 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	3		5
Interest Cost	4		9
Expected Return on Plan Assets	(2)		(4)
Amortization of Actuarial (Gain) Loss	0		0
Net Periodic Benefit Cost	5		$ 10
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		$ 4
Interest Cost	4		9
Expected Return on Plan Assets	(2)		(4)
Amortization of Actuarial (Gain) Loss	0		0
Net Periodic Benefit Cost	4		$ 9
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	1		$ 1
Interest Cost	0		0
Expected Return on Plan Assets	0		0
Amortization of Actuarial (Gain) Loss	0		0
Net Periodic Benefit Cost	$ 1		$ 1
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)