Investments (Schedule Of Amortized Cost And Fair Value Of HTM Fixed Maturities And Related OTTI Recognized In Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investment [Line Items]
Held to maturity, Amortized Cost	$ 13,136	$ 13,435
Held to maturity, Gross Unrealized Appreciation	158	51
Held to maturity, Gross Unrealized Depreciation	(54)	(227)
Held to maturity, at Fair Value	13,240	13,259
Held to maturity, OTTI recognized in AOCI	0	0
U.S. Treasury and agency
Investment [Line Items]
Held to maturity, Amortized Cost	1,144	1,185
Held to maturity, Gross Unrealized Appreciation	11	8
Held to maturity, Gross Unrealized Depreciation	(3)	(11)
Held to maturity, at Fair Value	1,152	1,182
Held to maturity, OTTI recognized in AOCI	0	0
Foreign
Investment [Line Items]
Held to maturity, Amortized Cost	1,503	1,549
Held to maturity, Gross Unrealized Appreciation	34	11
Held to maturity, Gross Unrealized Depreciation	(3)	(18)
Held to maturity, at Fair Value	1,534	1,542
Held to maturity, OTTI recognized in AOCI	0	0
Corporate securities
Investment [Line Items]
Held to maturity, Amortized Cost	2,543	2,601
Held to maturity, Gross Unrealized Appreciation	30	11
Held to maturity, Gross Unrealized Depreciation	(34)	(104)
Held to maturity, at Fair Value	2,539	2,508
Held to maturity, OTTI recognized in AOCI	0	0
Mortgage-backed securities
Investment [Line Items]
Held to maturity, Amortized Cost	2,484	2,524
Held to maturity, Gross Unrealized Appreciation	16	5
Held to maturity, Gross Unrealized Depreciation	(6)	(43)
Held to maturity, at Fair Value	2,494	2,486
Held to maturity, OTTI recognized in AOCI	0	0
States, municipalities, and political subdivisions
Investment [Line Items]
Held to maturity, Amortized Cost	5,462	5,576
Held to maturity, Gross Unrealized Appreciation	67	16
Held to maturity, Gross Unrealized Depreciation	(8)	(51)
Held to maturity, at Fair Value	5,521	5,541
Held to maturity, OTTI recognized in AOCI	$ 0	$ 0

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 12
-Sentence Column A

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Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as held-to-maturity that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

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-SubTopic 10
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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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