Investments (excluding Consolidated Investment Entities) - Fixed Maturities and Equity Securities, Repurchase Agreements and Securities Lending (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Available-for-sale Securities, Including Securities Pledged [Line Items]
Rate required of collateral as a percent of market value of loans securities	102.00%
Securities received as collateral	$ 132	$ 308
Payables under securities loan agreement, including collateral held	2,097	1,866
Securities pledged as collateral
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fair value of loaned securities	1,809	1,854
Short-term Investments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Securities received as collateral	1,739	1,589
Cash collateral, included in Payables
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 1,739	$ 1,589
Mortgage-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Percentage collateralized of mortgage backed securities including interest-only strip or principal-only strip	40.50%	43.20%
U.S. Treasuries
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 445	$ 587
U.S. government agencies and authorities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	9	5
U.S. corporate public securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	1,016	967
Short-term Investments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	0	0
Foreign corporate public securities and foreign governments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	401	338
Payables under securities loan agreements
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 1,871	$ 1,897

The fair value of collateral received by the entity associated with securities borrowed that must be returned if the counterparty fulfills its obligations. It appears on the balance sheet as a liability and has a corresponding asset that appears on the balance sheet called Securities Received as Collateral.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Fair value of the securities pledged as collateral against securities loaned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226013-175313

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The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 10
-Section 05
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=64836671&loc=d3e93645-111703

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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- Definition

Percent Collateralized Mortgage Backed Securities including Interest-Only Strip or Principal-Only Strip

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