Investments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2014	Dec. 31, 2013
Decrease in gross AFS securities unrealized losses	$ (607)
Number of partnerships in alternative investment portfolio	126	121
Investment commitments	1,000
Investment commitments for limited partnerships	586
Investment commitments for private placements	223
Investment commitments for mortgage loans on real estate	207
Mortgage loans on real estate [Member]
Largest mortgage loan concentration in geographic region	32.00%	32.00%
Federal Home Loan Mortgage Corporation
Fair value	2,600	2,600
Concentration risk, percentage	3.00%	3.00%
Fannie Mae
Fair value	1,600	1,700
Concentration risk, percentage	2.00%	2.00%
Electric Industry [Member]
Fair value	9,300	8,700
Concentration risk, percentage	9.00%	9.00%
Banking Industry [Member]
Fair value	5,000	5,000
Concentration risk, percentage	5.00%	5.00%
Corporate bonds [Member]
Percentage of fair value rated as investment grade	96.00%	96.00%
Amortized cost of portfolio rated below investment grade	3,100	3,000
Fair value of portfolio rated below investment grade	3,100	2,900
CDOs [Member]
Percentage of fair value rated as investment grade	95.00%	94.00%
Amortized cost of portfolio rated below investment grade	15	16
Fair value of portfolio rated below investment grade	$ 13	$ 13
Mortgage-backed securities [Member]
Projected default rate on existing delinquencies on MBS (low end of range)	10.00%
Projected default rate on existing delinquencies on MBS (high end of range)	100.00%
Severity of second lien loans	100.00%
Severity of first lien loans	30.00%

Amortized cost of portfolio rated below investment grade.

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This item represents the change in gross unrealized holding gain or loss on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

+ References

No definition available.

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Percentage of the fair value of portfolio that was rated investment grade as of balance sheet date.

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Fair value of portfolio rated below investment grade.

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This item represents total investment commitments as of the balance sheet date for fixed maturity available-for-sale securities, limited partnerships, real estate and mortgage loans on real estate.

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No definition available.

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This item represents investment commitments as of the balance sheet date for limited partnerships.

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This item represents investment commitments as of the balance sheet date for private placements.

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This item represents investment commitments as of the balance sheet date for mortgage loans.

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Largest concentration percentage of mortgage loans on commercial real estate throughout the U.S.

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Number of partnerships represented in alternative investment portfolio.

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- Definition

This item represents the default rate (as a percentage) of the underlying assets in the security that was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings (high end of range).

+ References

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- Definition

This item represents the loss severity as a percentage of first lien loans that was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings.

+ References

No definition available.

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This item represents the loss severity as a percentage of defaulted second lien loans that was considered as one of the potential factors in reaching a conclusion that the available-for-sale investments are other than temporarily impaired and the amount of such impairment determined to be related to credit loss recognized in earnings.

+ References

No definition available.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

+ References

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

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-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Subparagraph a, f, g

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