Intangible Assets (Estimated Amortization Expense Over Next Five Years) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
2021, Other intangible assets	$ 286
2022, Other intangible assets	284
2023, Other intangible assets	267
2024, Other intangible assets	244
2025, Other intangible assets	228
Total, Other intangible assets	1,309
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
2021, Other intangible assets	89
2022, Other intangible assets	101
2023, Other intangible assets	96
2024, Other intangible assets	90
2025, Other intangible assets	89
Total, Other intangible assets	465
The Chubb Corporation [Member]
Finite-Lived Intangible Assets [Line Items]
2021, Other intangible assets	197
2022, Other intangible assets	183
2023, Other intangible assets	171
2024, Other intangible assets	154
2025, Other intangible assets	139
Total, Other intangible assets	844
The Chubb Corporation [Member] | Agency distribution relationships and renewal rights [Member]
Finite-Lived Intangible Assets [Line Items]
2021, Other intangible assets	217
2022, Other intangible assets	197
2023, Other intangible assets	178
2024, Other intangible assets	160
2025, Other intangible assets	145
Total, Other intangible assets	897
The Chubb Corporation [Member] | Fair Value Adjustment to Acquired Loss Reserves [Member]
Finite-Lived Intangible Assets [Line Items]
2021, Other intangible assets	(20)
2022, Other intangible assets	(14)
2023, Other intangible assets	(7)
2024, Other intangible assets	(6)
2025, Other intangible assets	(6)
Total, Other intangible assets	(53)
Balance of FV adjustment on Unpaid Losses and Loss Expenses	$ 110	$ 145
Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	25 years