Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5% For A Continuous Twelve Month Period Or Longer) (Detail) $ in Millions	Sep. 30, 2015 USD ($) security	Dec. 31, 2014 USD ($)
Available For Sale Securities [Abstract]
Fixed-maturity securities held as available-for-sale, amortized cost	$ 6,265	$ 6,509
Available For Sale Securities	6,283	6,571
Held To Maturity Securities [Abstract]
Held-To-Maturity Securities Amortized Cost	2,707	2,757
Held-To-Maturity Securities Fair Value	$ 2,442	$ 2,632
> 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 \| security	7
Fixed-maturity securities held as available-for-sale, amortized cost	$ 13
Available For Sale Securities	$ 13
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position \| security	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 \| security	8
Fixed-maturity securities held as available-for-sale, amortized cost	$ 82
Available For Sale Securities	$ 65
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position \| security	0
Held-To-Maturity Securities Amortized Cost	$ 0
Held-To-Maturity Securities Fair Value	$ 0
> 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 \| security	5
Fixed-maturity securities held as available-for-sale, amortized cost	$ 5
Available For Sale Securities	$ 3
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position \| security	1
Held-To-Maturity Securities Amortized Cost	$ 575
Held-To-Maturity Securities Fair Value	$ 321
> 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 \| security	2
Fixed-maturity securities held as available-for-sale, amortized cost	$ 122
Available For Sale Securities	$ 17
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position \| security	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 \| security	22
Fixed-maturity securities held as available-for-sale, amortized cost	$ 222
Available For Sale Securities	$ 98
Held To Maturity Securities [Abstract]
Number of Held-To-Maturity Securities in unrealized loss position \| security	1
Held-To-Maturity Securities Amortized Cost	$ 575
Held-To-Maturity Securities Fair Value	$ 321

Percentage Of Fair Value Below Book Value Maximum

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Percentage Of Fair Value Below Book Value Minimum

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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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.

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-Publisher FASB

-Name Accounting Standards Codification

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Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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

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

-Publisher FASB

-Name Accounting Standards Codification

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

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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.

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