Intangible Assets (Estimated Amortization Expense Over Next Five Years) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
2018, Other intangible assets	$ 338
2019, Other intangible assets	294
2020, Other intangible assets	272
2021, Other intangible assets	259
2022, Other intangible assets	241
Total, Other intangible assets	1,404
Developed Technology Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
2018, Other intangible assets	83
2019, Other intangible assets	75
2020, Other intangible assets	67
2021, Other intangible assets	61
2022, Other intangible assets	57
Total, Other intangible assets	343
The Chubb Corporation [Member]
Finite-Lived Intangible Assets [Line Items]
2018, Other intangible assets	255
2019, Other intangible assets	219
2020, Other intangible assets	205
2021, Other intangible assets	198
2022, Other intangible assets	184
Total, Other intangible assets	1,061
The Chubb Corporation [Member] | Agency distribution relationships and renewal rights [Member]
Finite-Lived Intangible Assets [Line Items]
2018, Other intangible assets	325
2019, Other intangible assets	282
2020, Other intangible assets	241
2021, Other intangible assets	218
2022, Other intangible assets	198
Total, Other intangible assets	1,264
The Chubb Corporation [Member] | Developed Technology Rights [Member]
Finite-Lived Intangible Assets [Line Items]
2018, Other intangible assets	32
2019, Other intangible assets	0
2020, Other intangible assets	0
2021, Other intangible assets	0
2022, Other intangible assets	0
Total, Other intangible assets	32
The Chubb Corporation [Member] | Fair Value Adjustment to Acquired Loss Reserves [Member]
Finite-Lived Intangible Assets [Line Items]
2018, Other intangible assets	(102)
2019, Other intangible assets	(63)
2020, Other intangible assets	(36)
2021, Other intangible assets	(20)
2022, Other intangible assets	(14)
Total, Other intangible assets	(235)
Increase Decrease on Acquired Unpaid Losses and Loss Expenses	$ 309
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Minimum | The Chubb Corporation [Member] | Fair Value Adjustment to Acquired Loss Reserves [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	5 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	30 years
Maximum | The Chubb Corporation [Member] | Fair Value Adjustment to Acquired Loss Reserves [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	17 years