v3.8.0.1

Certain Long-Duration Contracts with Guarantees (Narrative) (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Annuity Contracts | Market Value Adjusted |  |
Net Amount at Risk by Product and Guarantee [Line Items] |  |
General Account Investment Option | $ 8,308 | $ 8,566

X
- Definition Value of the general accounts corresponding to the specified product, guarantee type and subset of the guarantee. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 80 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473 + Details
Name: | us-gaap_NetAmountAtRiskByProductAndGuaranteeGeneralAccountValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition 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. + Details
Name: | us-gaap_NetAmountAtRiskByProductAndGuaranteeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ProductOrServiceAxis=us-gaap_VariableAnnuityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_GuaranteeObligationsByNatureAxis=us-gaap_MarketValueGuaranteeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |