Derivative Financial Instruments and Off-balance sheet Financial Instruments (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 entity	Dec. 31, 2013
Derivative Financial Instruments and Off-balance sheet Financial Instruments
Term of credit default swaps (in years)	5 years
Credit Derivatives
Notional amount	$ 3,649invest_DerivativeNotionalAmount	$ 12,409invest_DerivativeNotionalAmount
The number of reference entities generally included in a CDX index	125
Credit default swaps
Credit Derivatives
Notional amount	180	185
Fair value	(7)	(13)
Credit default swaps \| Single name \| Investment grade corporate debt
Credit Derivatives
Notional amount	0	5
Fair value	0	0
Credit default swaps \| First-to-default Basket \| Municipal
Credit Derivatives
Notional amount	100	100
Fair value	(9)	(15)
Credit default swaps \| Index \| Investment grade corporate debt
Credit Derivatives
Notional amount	80	80
Fair value	2	2
AA \| Credit default swaps
Credit Derivatives
Notional amount	0	1
AA \| Credit default swaps \| Single name \| Investment grade corporate debt
Credit Derivatives
Notional amount	0	0
AA \| Credit default swaps \| First-to-default Basket \| Municipal
Credit Derivatives
Notional amount	0	0
AA \| Credit default swaps \| Index \| Investment grade corporate debt
Credit Derivatives
Notional amount	0	1
A \| Credit default swaps
Credit Derivatives
Notional amount	122	125
A \| Credit default swaps \| Single name \| Investment grade corporate debt
Credit Derivatives
Notional amount	0	5
A \| Credit default swaps \| First-to-default Basket \| Municipal
Credit Derivatives
Notional amount	100	100
A \| Credit default swaps \| Index \| Investment grade corporate debt
Credit Derivatives
Notional amount	22	20
BBB \| Credit default swaps
Credit Derivatives
Notional amount	52	55
BBB \| Credit default swaps \| Single name \| Investment grade corporate debt
Credit Derivatives
Notional amount	0	0
BBB \| Credit default swaps \| First-to-default Basket \| Municipal
Credit Derivatives
Notional amount	0	0
BBB \| Credit default swaps \| Index \| Investment grade corporate debt
Credit Derivatives
Notional amount	52	55
BB and lower \| Credit default swaps
Credit Derivatives
Notional amount	6	4
BB and lower \| Credit default swaps \| Single name \| Investment grade corporate debt
Credit Derivatives
Notional amount	0	0
BB and lower \| Credit default swaps \| First-to-default Basket \| Municipal
Credit Derivatives
Notional amount	0	0
BB and lower \| Credit default swaps \| Index \| Investment grade corporate debt
Credit Derivatives
Notional amount	$ 6	$ 4

The general number of entities included in a credit derivative index group.

No definition available.

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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- Definition

Term of the credit risk derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4K

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5708775-113959

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- Definition

Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4K

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5708775-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611

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