Investments (Narrative) (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) Security	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Security	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Investment [Line Items]
Net unrealized depreciation included in OCI	$ 3	$ 21	$ 3	$ 44
Unrealized appreciation(depreciation) portion of AOCI with OTTI included in AOCI	$ 7		$ 7		$ 10
Percentage of mortgage-backed securities represented by investments in US government agency bonds	81.00%		81.00%		81.00%
Total number of fixed maturities | Security	30,953		30,953
Number of equity securities in an unrealized loss position | Security	67		67
Total number of equity securities | Security	320		320
Largest single unrealized loss in the equity securities	$ 1		$ 1
Restricted assets in fixed maturities and short-term investments	21,200		21,200		$ 20,100
Restricted assets in cash	$ 122		$ 122		$ 103
Moodys Historical Mean Recovery Rate			42.00%
Company Assumed Recovery Rate			32.00%
Number of fixed maturities in an unrealized loss position | Security	7,924		7,924
Largest single unrealized loss in the fixed maturities	$ 5		$ 5
Corporate [Member]
Investment [Line Items]
Credit losses recognized in net income	1	7	2	24
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Credit losses recognized in net income	$ 0	$ 0	$ 0	$ 0