Investments (Securities Pledged as Collateral Related to Repurchase Reverse Repurchase Program) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	$ 53	$ 55
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	1,187	779
Obligation to Return Securities Received as Collateral	1,240	834
Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	37	42
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	339	279
Debt Security, Government, Non-US [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	5	5
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	100	95
US States and Political Subdivisions Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	11	3
Canadian and Canadian provincial governments
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	5
Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	224	54
Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	221	63
Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	152	10
JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	138	278
US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	13
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] | Canadian and Canadian provincial governments
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]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity Overnight [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0
Maturity up to 30 days [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 up to 30 days [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 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] | Canadian and Canadian provincial governments
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]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity up to 30 days [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	0
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	120	0
Obligation to Return Securities Received as Collateral	120	0
Maturity 30 to 90 Days [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 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	0	0
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] | Canadian and Canadian provincial governments
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]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	53	0
Maturity 30 to 90 Days [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	59	0
Maturity 30 to 90 Days [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	8	0
Maturity 30 to 90 Days [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0	0
Maturity 30 to 90 Days [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	0
Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	53	55
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	1,067	779
Obligation to Return Securities Received as Collateral	1,120	834
Maturity over 90 days [Member] | Corporate Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	37	42
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	339	279
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	5	5
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	100	95
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	11	3
Maturity over 90 days [Member] | Canadian and Canadian provincial governments
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned, Fair Value of Collateral	0	5
Maturity over 90 days [Member] | Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	171	54
Maturity over 90 days [Member] | Commercial Mortgage Backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	162	63
Maturity over 90 days [Member] | Residential mortgage-backed securities
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	144	10
Maturity over 90 days [Member] | JAPAN
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	138	$ 278
Maturity over 90 days [Member] | US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
FinancialAssetsSoldUnderAgreementsToRepurchaseGrossIncludingNotSubjectToMasterNettingArrangement	$ 13