Fair Value Disclosures (Fair Value of Equity Fund and Hedge Fund) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Fair Value of Investments that Calculate Net Asset Value
Fair Value, Investments	$ 3,388	$ 3,843
Private Equity Funds
Fair Value of Investments that Calculate Net Asset Value
Fair value of investment to be liquidated (less than 5 years)	141
Fair value of investment to be liquidated (5-10 years)	926
Fair value of investment to be liquidated (Over 10 years)	701
Fair Value, Investments	1,768	1,917
Real Estate Funds
Fair Value of Investments that Calculate Net Asset Value
Fair value of investment to be liquidated (less than 5 years)	97
Fair value of investment to be liquidated (5-10 years)	708
Fair value of investment to be liquidated (Over 10 years)	469
Fair Value, Investments	1,274	1,337
Long-short Equity Hedge Funds
Fair Value of Investments that Calculate Net Asset Value
Fair Value, Investments	$ 193	$ 422
Percent of investments redeemable at least quarterly	34.00%	34.00%
Percent of investments redeemable every six months	33.00%	51.00%
Percent of investments redeemable greater than six months	33.00%	15.00%
Long-short Equity Hedge Funds \| Gate restriction
Fair Value of Investments that Calculate Net Asset Value
Percent of investments that cannot be redeemed currently	26.00%
Fixed Income Funds
Fair Value of Investments that Calculate Net Asset Value
Fair Value, Investments	$ 52	$ 71
Redemption restriction period	90 days	90 days
Redemption frequency	three-month period basis	three-month period basis
Fixed Income Funds \| Gate restriction
Fair Value of Investments that Calculate Net Asset Value
Percent of investments that cannot be redeemed currently	73.00%
Event Driven Hedge Funds
Fair Value of Investments that Calculate Net Asset Value
Fair Value, Investments	$ 2	$ 2
Redemption restriction period	90 days	90 days
Redemption frequency	three-month period basis	three-month period basis
Multi-strategy Hedge Funds
Fair Value of Investments that Calculate Net Asset Value
Fair Value, Investments	$ 99	$ 94
Redemption restriction period	90 days	90 days
Redemption frequency	three-month period basis	three-month period basis
Multi-strategy Hedge Funds \| Lock up restrictions
Fair Value of Investments that Calculate Net Asset Value
Percent of investments that cannot be redeemed currently	21.00%
Multi-strategy Hedge Funds \| Lock up restrictions \| Minimum
Fair Value of Investments that Calculate Net Asset Value
Redemption restriction period	3 years

Fair value of investments that will be liquidated after ten years.

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Fair value of investments that will be liquidated within five to ten years.

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Fair value of investments that will be liquidated in the next five years.

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Percent of investments redeemable at least quarterly.

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Percent of investments redeemable every six months.

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Percent of investments redeemable greater than six months.

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Fair value of investments in certain entities that calculate net asset value per share, including, but not limited to, by unit, membership interest, or other ownership interest. Investments include, but are not limited to, investments in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=SL6742756-110258

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States the frequency (for example, annually, semi-annually, quarterly) with which the entity can redeem its investment, or portion thereof, for each of those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments), by major category.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=SL6742756-110258

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Line items represent financial 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.

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The percentage of the total value of investments that cannot be redeemed because of a redemption restriction as of the statement of financial position date.

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Remaining period of a redemption restriction related to investments for which net asset value per share is calculated, 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 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=SL6742756-110258

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