Investments (Schedule Of Sources Of Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Investment Income [Line Items]
Gross investment income									$ 3,289	$ 3,006	$ 2,308
Investment expenses									(164)	(141)	(114)
Net investment income	$ 797	$ 813	$ 770	$ 745	$ 744	$ 739	$ 708	$ 674	3,125	2,865	2,194
Amortization of Debt Issuance Costs and Discounts									694	737	158
The Chubb Corporation [Member]
Net Investment Income [Line Items]
Amortization of Debt Issuance Costs and Discounts									(332)	(393)
Fixed Maturities [Member]
Net Investment Income [Line Items]
Gross investment income									2,987	2,779	2,157
Short-term investments
Net Investment Income [Line Items]
Gross investment income									131	93	49
Equity securities
Net Investment Income [Line Items]
Gross investment income									38	36	16
Other Investments [Member]
Net Investment Income [Line Items]
Gross investment income									$ 133	$ 98	$ 86