Investments (Narrative) (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Security	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Security	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Investment [Line Items]
Net unrealized appreciation (depreciation) included in OCI	$ (2)	$ 1	$ (6)	$ (2)
Unrealized appreciation(depreciation) portion of AOCI with OTTI included in AOCI	$ 1		$ 1		$ 7
Percentage of mortgage-backed securities represented by investments in US government agency bonds	82.00%		82.00%		83.00%
Moodys Historical Mean Recovery Rate			42.00%
Company Assumed Recovery Rate			32.00%
Operating Lease, Impairment Loss			$ 22
Available-for-sale Equity Securities, Amortized Cost Basis	$ 843		843		$ 737
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax					212
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax					12
Equity securities, at fair value	$ 843		$ 843		937
Total number of fixed maturities | Security	31,196		31,196
Number of fixed maturities in an unrealized loss position | Security	17,978		17,978
Largest single unrealized loss in the fixed maturities	$ 13		$ 13
Restricted assets in fixed maturities and short-term investments	21,000		21,000		23,300
Restricted assets in cash	104		104		$ 123
Corporate securities
Investment [Line Items]
Credit losses recognized in net income	8	3	9	5
Mortgage-backed securities
Investment [Line Items]
Credit losses recognized in net income	$ 0	$ 0	0	$ 0
Junior Subordinated Debt [Member] | Chubb INA Senior Notes Due 2037 [Member]
Investment [Line Items]
Gain (Loss) on Extinguishment of Debt			$ (36)