Investments (Narrative) (Details) $ in Thousands	3 Months Ended
Mar. 31, 2019 USD ($) securities	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) securities
Investment Narrative [Line Items]
Proceeds From Sale Of Available For Sale Securities Sold At Loss	$ 1,246,600	$ 1,263,600
Sales of fixed maturity securities available-for-sale	3,139,794	1,898,722
Securities Sold under Agreements to Repurchase, Collateral, Right to Reclaim Cash	28,700		$ 28,600
Net Amount Assets Liabilities From Repurchase Reverse Repurchase Agreements	400
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held	$ 3,700
Policy Loans Percent Of Total Investments	2.30%		2.50%
Mortgage Loan Percent Of Cash And Invested Assets			9.10%
Available-for-sale Securities, Realized Losses, Excluding Other than Temporary Impairments	$ 18,723	20,380
ProceedsFromSaleOfAvailableForSaleEquitySecuritiesSoldAtLoss		28,400
Available-for-sale Equity Securities, Gross Unrealized Loss	1	950
Available-for-sale Securities, Gross Realized Gains	$ 28,045	10,966
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions \| securities	1,585		3,109
Securities As Percentage Of Consolidated Stockholder Equity	10.00%
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%		100.00%
Funds Withheld At Interest Percent Of Total Investments	10.20%		10.60%
Funds withheld at interest	$ 5,729,838		$ 5,761,471
Funds Held Under Reinsurance Agreements Asset Specific Client	3,700,000
Gain (Loss) on Sale of Equity Investments	$ 3,744	$ (4,137)
Other Invested Assets Percent Of Invested Assets	3.60%		3.50%
CALIFORNIA
Investment Narrative [Line Items]
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	17.70%
TEXAS
Investment Narrative [Line Items]
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	11.80%
GEORGIA
Investment Narrative [Line Items]
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	7.10%
CANADA
Investment Narrative [Line Items]
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	2.90%
UNITED KINGDOM
Investment Narrative [Line Items]
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	0.50%

Funds Withheld At Interest concentrated with one client.

No definition available.

Name:	rga_FundsHeldUnderReinsuranceAgreementsAssetSpecificClient
Namespace Prefix:	rga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Funds Withheld At Interest As A Percentage Of Total Investments

+ References

No definition available.

+ Details

Name:	rga_FundsWithheldAtInterestPercentOfTotalInvestments
Namespace Prefix:	rga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

Name:	rga_InvestmentNarrativeLineItems
Namespace Prefix:	rga_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Mortgage Loans as a Percent Of total Cash And Invested Assets

+ References

No definition available.

+ Details

Name:	rga_MortgageLoanPercentOfCashAndInvestedAssets
Namespace Prefix:	rga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount represents the total percentage of each property type in comparison to the total of mortgage loans whose balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

No definition available.

+ Details

Name:	rga_MortgageLoansOnRealEstateCommercialAndConsumerNetPercentageOfTotal
Namespace Prefix:	rga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Net amount, after affects of netting, from repurchase and reverse repurchase agreements presented on the Balance sheet.

+ References

No definition available.

+ Details

Name:	rga_NetAmountAssetsLiabilitiesFromRepurchaseReverseRepurchaseAgreements
Namespace Prefix:	rga_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other Invested Assets Percent Of Invested Assets

+ References

No definition available.

+ Details

Name:	rga_OtherInvestedAssetsPercentOfInvestedAssets
Namespace Prefix:	rga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Policy Loans as a percentage of total investments.

+ References

No definition available.

+ Details

Name:	rga_PolicyLoansPercentOfTotalInvestments
Namespace Prefix:	rga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Proceeds From Sale Of Available For Sale Equity Securities Sold At Loss

+ References

No definition available.

+ Details

Name:	rga_ProceedsFromSaleOfAvailableForSaleEquitySecuritiesSoldAtLoss
Namespace Prefix:	rga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

No definition available.

+ Details

Name:	rga_ProceedsFromSaleOfAvailableForSaleSecuritiesSoldAtLoss
Namespace Prefix:	rga_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Securities as percentage of consolidated stockholder equity.

+ References

No definition available.

+ Details

Name:	rga_SecuritiesAsPercentageOfConsolidatedStockholderEquity
Namespace Prefix:	rga_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale equity securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleEquitySecuritiesGrossUnrealizedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of loss realized on the sale of debt or equity securities classified as available-for-sale. Excludes other than temporary impairments (OTTI).

+ References

No definition available.

+ Details

Name:	us-gaap_AvailableforsaleSecuritiesGrossRealizedLossesExcludingOtherThanTemporaryImpairments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

+ Details

Name:	us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of the reinsurer's funds held on its behalf by the ceding insurer, including funds held in trust, under reinsurance treaties or contracts with the assuming insurer as security for the payment of the obligations thereunder.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.2,10)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_FundsHeldUnderReinsuranceAgreementsAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The difference between the carrying value and the sale price of equity securities, not separately or otherwise categorized as trading or available-for-sale. This element includes investments in which the entity holds a small ownership stake (generally, less than 20% of the shares outstanding) and cannot exert significant influence.

+ References

No definition available.

+ Details

Name:	us-gaap_GainLossOnSaleOfEquityInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of right to receive cash collateral under master netting arrangements that have not been offset against securities sold under agreement to repurchase.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_SecuritiesSoldUnderAgreementsToRepurchaseCollateralRightToReclaimCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	invest_InvestmentGeographicRegionAxis=stpr_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentGeographicRegionAxis=stpr_TX
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentGeographicRegionAxis=stpr_GA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentGeographicRegionAxis=country_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentGeographicRegionAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: