Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5%) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Available For Sale Securities [Abstract]
Available-For-Sale Securities Amortized Cost	$ 6,647	$ 6,122
Available-For-Sale Securities Fair Value	6,572	6,221
Held To Maturity Securities [Abstract]
Held-To-Maturity Securities Fair Value	2,690	2,674
> 5% To 15% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	5.00%
Percentage Of Fair Value Below Book Value Maximum	15.00%
> 5% To 15% [Member] \| Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of Available-For-Sale Securities in unrealized loss position	13
Available-For-Sale Securities Amortized Cost	114
Available-For-Sale Securities Fair Value	104
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	0
Held-To-Maturity Securities Amortized Cost	0
Held-To-Maturity Securities Fair Value	0
> 15% To 25% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	15.00%
Percentage Of Fair Value Below Book Value Maximum	25.00%
> 15% To 25% [Member] \| Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of Available-For-Sale Securities in unrealized loss position	10
Available-For-Sale Securities Amortized Cost	118
Available-For-Sale Securities Fair Value	94
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	1
Held-To-Maturity Securities Amortized Cost	575
Held-To-Maturity Securities Fair Value	478
> 25% To 50% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	25.00%
Percentage Of Fair Value Below Book Value Maximum	50.00%
> 25% To 50% [Member] \| Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of Available-For-Sale Securities in unrealized loss position	5
Available-For-Sale Securities Amortized Cost	10
Available-For-Sale Securities Fair Value	6
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	0
Held-To-Maturity Securities Amortized Cost	0
Held-To-Maturity Securities Fair Value	0
> 50% [Member]
Held To Maturity Securities [Abstract]
Percentage Of Fair Value Below Book Value Minimum	50.00%
> 50% [Member] \| Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of Available-For-Sale Securities in unrealized loss position	11
Available-For-Sale Securities Amortized Cost	78
Available-For-Sale Securities Fair Value	17
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	0
Held-To-Maturity Securities Amortized Cost	0
Held-To-Maturity Securities Fair Value	0
Greater Than 5% [Member] \| Unrealized loss position > 12 months
Available For Sale Securities [Abstract]
Number of Available-For-Sale Securities in unrealized loss position	39
Available-For-Sale Securities Amortized Cost	320
Available-For-Sale Securities Fair Value	221
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position	1
Held-To-Maturity Securities Amortized Cost	575
Held-To-Maturity Securities Fair Value	$ 478

Percentage Of Fair Value Below Book Value Maximum

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Percentage Of Fair Value Below Book Value Minimum

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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-Name FASB Staff Position (FSP)

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-Paragraph 7

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

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Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (b)(3)

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-Name Emerging Issues Task Force (EITF)

-Number 03-1

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-Subparagraph b(3)

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- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 43

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-Chapter 3

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-Number 115

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-Number 115

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-Name Accounting Standards Codification

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-Name Accounting Research Bulletin (ARB)

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This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

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Disclosure regarding factors used to determine that the impairment of securities categorized as held-to-maturity where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the held-to-maturity investments determined to be temporarily impaired.

+ References

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