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Reinsurance Reinsurance (Net Amount at Risk and 100 Percent Mortality) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Guaranteed Minimum Benefits [Line Items] |  |
Average attained age of all policyholders under all benefits reinsured, years | 70 years |
GLB |  |
Guaranteed Minimum Benefits [Line Items] |  |
Net Amount at Risk | $ 691 | $ 800
GMDB |  |
Guaranteed Minimum Benefits [Line Items] |  |
Net Amount at Risk | $ 279 | 341
Mortality percentage according to Annuity 2000 mortality table | 100.00% |
GMDB with Both Risk(GMDB and GLB) [Member] |  |
Guaranteed Minimum Benefits [Line Items] |  |
Net Amount at Risk | $ 81 | 88
GLB with Both Risk(GLB and GMDB) [Member] |  |
Guaranteed Minimum Benefits [Line Items] |  |
Net Amount at Risk | $ 392 | $ 464
Minimum | GLB |  |
Guaranteed Minimum Benefits [Line Items] |  |
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate | 4.25% |
Minimum | GMDB |  |
Guaranteed Minimum Benefits [Line Items] |  |
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate | 4.00% |
Minimum | GLB with Both Risk(GLB and GMDB) [Member] |  |
Guaranteed Minimum Benefits [Line Items] |  |
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate | 4.25% |
Maximum | GLB |  |
Guaranteed Minimum Benefits [Line Items] |  |
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate | 4.75% |
Maximum | GMDB |  |
Guaranteed Minimum Benefits [Line Items] |  |
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate | 4.50% |
Maximum | GLB with Both Risk(GLB and GMDB) [Member] |  |
Guaranteed Minimum Benefits [Line Items] |  |
Long-Duration Contracts, Assumptions by Product and Guarantee, Discount Rate | 4.75% |

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- Definition Percentage discount rate used to calculate present value of an expected stream of future payments, which is included in the calculation of the amount of the specified guaranteed benefit obligation as of the balance sheet date. + 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 (c) -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6482852&loc=d3e14931-158439 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 55 -Paragraph 15 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389 + Details
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- Definition Actuarially determined death rate of policyholders, which is included in determining the amount of the specified guaranteed benefit obligation as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 55 -Paragraph 15 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 80 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6482852&loc=d3e14931-158439 + Details
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- Definition Net amount at risk, representing the guaranteed benefit in excess of the current account balance 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)(3),(5) -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389 + Details
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- Definition Weighted average attained age of policyholders or contract holders in the specified guarantee type and subset of guarantee class, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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)(5)) -URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389 + Details
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