Intangible Assets (Estimated Amortization Expense Over Next Five Years) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
2020, Other intangible assets	$ 290
2021, Other intangible assets	280
2022, Other intangible assets	275
2023, Other intangible assets	261
2024, Other intangible assets	239
Total, Other intangible assets	1,345
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
2020, Other intangible assets	86
2021, Other intangible assets	84
2022, Other intangible assets	93
2023, Other intangible assets	91
2024, Other intangible assets	85
Total, Other intangible assets	439
The Chubb Corporation [Member]
Finite-Lived Intangible Assets [Line Items]
2020, Other intangible assets	204
2021, Other intangible assets	196
2022, Other intangible assets	182
2023, Other intangible assets	170
2024, Other intangible assets	154
Total, Other intangible assets	906
The Chubb Corporation [Member] | Agency distribution relationships and renewal rights [Member]
Finite-Lived Intangible Assets [Line Items]
2020, Other intangible assets	239
2021, Other intangible assets	216
2022, Other intangible assets	196
2023, Other intangible assets	177
2024, Other intangible assets	159
Total, Other intangible assets	987
The Chubb Corporation [Member] | Fair Value Adjustment to Acquired Loss Reserves [Member]
Finite-Lived Intangible Assets [Line Items]
2020, Other intangible assets	(35)
2021, Other intangible assets	(20)
2022, Other intangible assets	(14)
2023, Other intangible assets	(7)
2024, Other intangible assets	(5)
Total, Other intangible assets	(81)
Balance of FV adjustment on Unpaid Losses and Loss Expenses	$ 145	$ 207
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	25 years