Investments (Narrative) (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) Security	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Security	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Investment [Line Items]
Net unrealized appreciation (depreciation) included in OCI	$ 0	$ 3	$ 4	$ 3
Unrealized appreciation(depreciation) portion of AOCI with OTTI included in AOCI	$ 3		$ 3		$ 7
Percentage of mortgage-backed securities represented by investments in US government agency bonds	81.00%		81.00%		83.00%
Moodys Historical Mean Recovery Rate			42.00%
Company Assumed Recovery Rate			32.00%
Operating Lease, Impairment Loss	$ 22		$ 22
Available-for-sale Equity Securities, Amortized Cost Basis	933		933		$ 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 (cost – $933 and $737)	$ 933		$ 933		937
Total number of fixed maturities | Security	31,062		31,062
Number of fixed maturities in an unrealized loss position | Security	17,926		17,926
Largest single unrealized loss in the fixed maturities	$ 11		$ 11
Restricted assets in fixed maturities and short-term investments	21,200		21,200		23,300
Restricted assets in cash	101		101		$ 123
Corporate [Member]
Investment [Line Items]
Credit losses recognized in net income	1	1	1	2
Collateralized Mortgage Backed Securities [Member]
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)		$ (36)