Investments (Narrative) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) Security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Investment [Line Items]
Net unrealized appreciation (depreciation) included in OCI	$ 0	$ 23
Unrealized appreciation (depreciation) portion of AOCI with OTTI included in AOCI	$ 10		$ 10
Percentage of mortgage-backed securities represented by investments in US government agency bonds	82.00%		81.00%
Total number of fixed maturities | Security	31,098
Number of equity securities in an unrealized loss position | Security	70
Total number of equity securities | Security	325
Largest single unrealized loss in the equity securities	$ 1
Restricted assets in fixed maturities and short-term investments	20,600		$ 20,100
Restricted assets in cash	$ 97		$ 103
Moodys Historical Mean Recovery Rate	42.00%
Company Assumed Recovery Rate	32.00%
Number of fixed maturities in an unrealized loss position | Security	9,408
Largest single unrealized loss in the fixed maturities	$ 6
Corporate [Member]
Investment [Line Items]
Credit losses recognized in net income	1	17
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Credit losses recognized in net income	$ 0	$ 0