Investments (excluding Consolidated Investment Entities) - Fixed Maturities and Equity Securities, Repurchase Agreements and Securities Lending (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Including Securities Pledged [Line Items]
Securities received as collateral	$ 308	$ 743
Payables under securities loan agreement, including collateral held	1,866	969
Securities pledged
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fair value of loaned securities	1,854	1,133
Short-term investments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Securities received as collateral	1,589	425
Payables under securities loan agreement, including collateral held
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 1,589	$ 425
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	43.20%	46.40%
U.S. Treasuries
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 587	$ 701
U.S. government agencies and authorities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	5	4
U.S. corporate public securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	967	294
Short-term investments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	0	1
Foreign corporate public securities and foreign governments
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	338	168
Payables Under Securities Loan Agreements
Available-for-sale Securities, Including Securities Pledged [Line Items]
Payables under securities loan agreement, including collateral held	$ 1,897	$ 1,168

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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