Investments (Securities Pledged as Collateral Related to Repurchase Reverse Repurchase Program) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	$ 1,040	$ 732
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	1,683	1,333
Obligation to Return Securities Received as Collateral	2,723	2,065
Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	399	135
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	513	553
Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	20	18
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	99	106
US States and Political Subdivisions Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	6	11
Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	24	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	318	229
Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	47	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	266	221
Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	14	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	51	52
JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	521	568
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	376	158
US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	9	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	60	14
Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Obligation to Return Securities Received as Collateral	0	0
Maturity Overnight [Member] | Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
Maturity Overnight [Member] | Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	75	88
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Obligation to Return Securities Received as Collateral	75	88
Maturity up to 30 days [Member] | Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	75	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
Maturity up to 30 days [Member] | Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	88
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	440	107
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Obligation to Return Securities Received as Collateral	440	107
Maturity 30 to 90 Days [Member] | Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	134	94
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	11	13
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
Maturity 30 to 90 Days [Member] | Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	295	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	525	537
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	1,683	1,333
Obligation to Return Securities Received as Collateral	2,208	1,870
Maturity over 90 days [Member] | Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	190	41
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	513	553
Maturity over 90 days [Member] | Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	9	5
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	99	106
Maturity over 90 days [Member] | US States and Political Subdivisions Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	6	11
Maturity over 90 days [Member] | Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	24	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	318	229
Maturity over 90 days [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	47	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	266	221
Maturity over 90 days [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	14	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	51	52
Maturity over 90 days [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	226	480
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	376	158
Maturity over 90 days [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	9	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	$ 60	$ 14