Employee Benefit Plans - Investments Measured at NAV (Details) - NAV - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Investments measured at NAV
Fair value of investment measured at NAV	$ 9,854	$ 9,136
Hedge funds and hedge fund-related strategies
Investments measured at NAV
Fair value of investment measured at NAV	5,588	$ 5,264
Unfunded commitments	$ 76
Hedge funds and hedge fund-related strategies \| Minimum
Investments measured at NAV
Redemption notice period	2 days	2 days
Hedge funds and hedge fund-related strategies \| Maximum
Investments measured at NAV
Redemption notice period	180 days	180 days
Commingled funds, private equity and private equity-related instruments
Investments measured at NAV
Fair value of investment measured at NAV	$ 1,834	$ 1,591
Unfunded commitments	$ 393
Commingled funds, private equity and private equity-related instruments \| Minimum
Investments measured at NAV
Redemption notice period	2 days	2 days
Commingled funds, private equity and private equity-related instruments \| Maximum
Investments measured at NAV
Redemption notice period	30 days	30 days
Fixed income and fixed income-related instruments
Investments measured at NAV
Fair value of investment measured at NAV	$ 958	$ 769
Unfunded commitments	$ 254
Fixed income and fixed income-related instruments \| Minimum
Investments measured at NAV
Redemption notice period	15 days	15 days
Fixed income and fixed income-related instruments \| Maximum
Investments measured at NAV
Redemption notice period	90 days	90 days
Real assets
Investments measured at NAV
Fair value of investment measured at NAV	$ 758	$ 807
Unfunded commitments	203
Other
Investments measured at NAV
Fair value of investment measured at NAV	$ 716	$ 705
Other \| Minimum
Investments measured at NAV
Redemption notice period	2 days	2 days
Other \| Maximum
Investments measured at NAV
Redemption notice period	90 days	90 days

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 35
-Paragraph 54B
-URI http://asc.fasb.org/extlink&oid=117332851&loc=SL7495116-110257

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- Definition

Notice period the entity is required to deliver before it can redeem an investment calculated using net asset value per share, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Includes, but is not limited to, investments calculated by per unit, per membership interest, other equity or ownership interest and alternative investments.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
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-URI http://asc.fasb.org/extlink&oid=117815213&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.

+ References

No definition available.

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- Definition

The amount of unfunded commitments for which the entity is obligated, to 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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=SL6742756-110258

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