Investments (Narrative) (Detail) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) Security	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Investment [Line Items]
Net unrealized appreciation (depreciation) included in OCI	$ 9	$ (4)
Unrealized appreciation(depreciation) portion of AOCI with OTTI included in AOCI	$ 3		$ 1
Percentage of mortgage-backed securities represented by investments in US government agency bonds	82.00%		81.00%
Company Assumed Recovery Rate	32.00%
Moodys Historical Mean Recovery Rate	42.00%
Total number of fixed maturities \| Security	30,335
Number of fixed maturities in an unrealized loss position \| Security	10,095
Largest single unrealized loss in the fixed maturities	$ 6
Restricted assets in fixed maturities and short-term investments	22,000		$ 21,000
Restricted assets in cash	122		$ 93
Corporate securities
Investment [Line Items]
Credit losses recognized in net income	6	0
Mortgage-backed securities
Investment [Line Items]
Credit losses recognized in net income	$ 0	$ 0

AOCI Portion Attributable to change of FV of investments with OTTI

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Company assumed recovery rate.

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Number of fixed maturities in an unrealized loss position.

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Largest single unrealized loss in the fixed maturities.

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Total number of fixed maturities.

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Moodys historical mean recovery rate.

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Percentage of mortgage-backed securities represented by investments in US Government Agency bonds.

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Net unrealized appreciation included in other comprehensive income relating to securities upon which a credit impairment was recorded.

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Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of increase (decrease) in the cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (loss).

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Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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