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	Sep. 30, 2017	Dec. 31, 2016
Investment [Line Items]
Held to maturity, Amortized Cost	$ 10,160	$ 10,644
Held to maturity, Gross Unrealized Appreciation	216	148
Held to maturity, Gross Unrealized Depreciation	(11)	(122)
Held to maturity, at Fair Value	10,365	10,670
Held to maturity, OTTI recognized in AOCI		0
U.S. Treasury And Agency [Member]
Investment [Line Items]
Held to maturity, Amortized Cost	611	655
Held to maturity, Gross Unrealized Appreciation	13	9
Held to maturity, Gross Unrealized Depreciation	(3)	(3)
Held to maturity, at Fair Value	621	661
Held to maturity, OTTI recognized in AOCI	0	0
Foreign [Member]
Investment [Line Items]
Held to maturity, Amortized Cost	616	640
Held to maturity, Gross Unrealized Appreciation	28	28
Held to maturity, Gross Unrealized Depreciation	0	(1)
Held to maturity, at Fair Value	644	667
Held to maturity, OTTI recognized in AOCI	0	0
Corporate [Member]
Investment [Line Items]
Held to maturity, Amortized Cost	2,531	2,771
Held to maturity, Gross Unrealized Appreciation	63	50
Held to maturity, Gross Unrealized Depreciation	(5)	(26)
Held to maturity, at Fair Value	2,589	2,795
Held to maturity, OTTI recognized in AOCI	0	0
Collateralized Mortgage Backed Securities [Member]
Investment [Line Items]
Held to maturity, Amortized Cost	1,223	1,393
Held to maturity, Gross Unrealized Appreciation	35	35
Held to maturity, Gross Unrealized Depreciation	0	0
Held to maturity, at Fair Value	1,258	1,428
Held to maturity, OTTI recognized in AOCI	0	0
States, Municipalities, And Political Subdivisions [Member]
Investment [Line Items]
Held to maturity, Amortized Cost	5,179	5,185
Held to maturity, Gross Unrealized Appreciation	77	26
Held to maturity, Gross Unrealized Depreciation	(3)	(92)
Held to maturity, at Fair Value	5,253	5,119
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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 9A
-URI http://asc.fasb.org/extlink&oid=82896770&loc=SL6284427-111562

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Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 944
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-Paragraph 1
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Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity.

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Fair value of investments in debt securities classified as held-to-maturity.

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