Investments (Mortgage Loans - Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) Contracts	Dec. 31, 2018 USD ($) Contracts	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	$ 867	$ 944
Financing Receivable, Purchase	4,800	3,500	$ 3,100
Impaired Financing Receivable, Average Recorded Investment	$ 607	$ 481
Percentage of Mortgage Loans Classified as Performing	99.00%	99.00%
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 0	$ 0	5
Financing Receivable, Modifications, Number of Contracts \| Contracts	0	0
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 406	$ 358	285
Financing Receivable, Modifications, Number of Contracts \| Contracts	396	440
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 97	$ 96
Financing Receivable, Troubled Debt Restructuring, Postmodification	87	92
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 201	$ 123	$ 32
Financing Receivable, Modifications, Number of Contracts \| Contracts	3
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 111
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 111

The percentage of all mortgage loans that are classified as performing.

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+ References

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

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Amount, after troubled debt restructuring, of modified financing receivable.

+ References

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- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

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- Definition

Amount of increase from purchase of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 11
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919244-210447

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-Publisher FASB
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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

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