Intangible Assets (Estimated Amortization Expense Over Next Five Years) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
2019, Other intangible assets	$ 298
2020, Other intangible assets	280
2021, Other intangible assets	266
2022, Other intangible assets	246
2023, Other intangible assets	232
Total, Other intangible assets	1,322
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
2019, Other intangible assets	80
2020, Other intangible assets	76
2021, Other intangible assets	70
2022, Other intangible assets	64
2023, Other intangible assets	62
Total, Other intangible assets	352
The Chubb Corporation [Member]
Finite-Lived Intangible Assets [Line Items]
2019, Other intangible assets	218
2020, Other intangible assets	204
2021, Other intangible assets	196
2022, Other intangible assets	182
2023, Other intangible assets	170
Total, Other intangible assets	970
The Chubb Corporation [Member] | Agency distribution relationships and renewal rights [Member]
Finite-Lived Intangible Assets [Line Items]
2019, Other intangible assets	280
2020, Other intangible assets	239
2021, Other intangible assets	216
2022, Other intangible assets	196
2023, Other intangible assets	177
Total, Other intangible assets	1,108
The Chubb Corporation [Member] | Fair Value Adjustment to Acquired Loss Reserves [Member]
Finite-Lived Intangible Assets [Line Items]
2019, Other intangible assets	(62)
2020, Other intangible assets	(35)
2021, Other intangible assets	(20)
2022, Other intangible assets	(14)
2023, Other intangible assets	(7)
Total, Other intangible assets	(138)
Balance of FV adjustment on Unpaid Losses and Loss Expenses	$ 207	$ 309
Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	30 years