Investments (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2022 USD ($) loan security item	Dec. 31, 2021 USD ($) loan security item
Investments [Line Items]
Increase (decrease) in gross AFS securities unrealized losses	$ 2,500.0
Number of partnerships in alternative investment portfolio \| item	318	311
Alternative investments as a percentage of overall invested assets	2.00%	2.00%
Amortized cost	$ 107,622.0	$ 105,177.0
Fair Value	110,695.0	118,746.0
Fair value of collateral received that we are permitted to sell or re-pledge	22.0
Investment commitments	3,100.0
Investment commitments for limited partnerships	1,500.0
Investment commitments for mortgage loans on real estate	740.0
Investment commitments for private placements	$ 854.0
Minimum [Member]
Investments [Line Items]
Percentage of the fair value of securities obtained as collateral under reverse repurchase agreements	80.00%
Maximum [Member]
Investments [Line Items]
Percentage of the fair value of securities obtained as collateral under reverse repurchase agreements	95.00%
Federal Home Loan Mortgage Corporation [Member] \| Investments [Member]
Investments [Line Items]
Fair value	$ 857,000.0	$ 953,000.0
Federal National Mortgage Association [Member] \| Investments [Member]
Investments [Line Items]
Fair value	$ 854.0
Corporate Bonds [Member]
Investments [Line Items]
Percentage of fair value rated as investment grade	96.00%	96.00%
Corporate Bonds [Member] \| External Credit Rating, Non Investment Grade [Member]
Investments [Line Items]
Amortized cost		$ 3,700.0
Fair Value	$ 3,600.0	3,800.0
Federal National Mortgage Association [Member] \| Investments [Member]
Investments [Line Items]
Fair value		$ 926.0
Federal National Mortgage Association [Member] \| Federal Home Loan Mortgage Corporation [Member] \| Investments [Member]
Investments [Line Items]
Concentration risk, percentage	1.00%	1.00%
Federal National Mortgage Association [Member] \| Federal National Mortgage Association [Member] \| Investments [Member]
Investments [Line Items]
Concentration risk, percentage	1.00%	1.00%
Federal National Mortgage Association [Member] \| Consumer Non-Cyclical Industry [Member] \| Investments [Member]
Investments [Line Items]
Fair value	$ 17,800.0	$ 19,600.0
Concentration risk, percentage	12.00%	13.00%
Federal National Mortgage Association [Member] \| Financial Service [Member]
Investments [Line Items]
Fair value	$ 18.1	$ 19.2
Federal National Mortgage Association [Member] \| Financial Service [Member] \| Investments [Member]
Investments [Line Items]
Concentration risk, percentage	13.00%	12.00%
Commercial [Member]
Investments [Line Items]
Number of impaired loans \| security	4	4
Impaired financing receivable, principal balance	$ 1.0	$ 1.0
Commercial [Member] \| Federal National Mortgage Association [Member] \| Geographic Concentration Risk [Member] \| Mortgage Loans On Real Estate [Member] \| California [Member]
Investments [Line Items]
Concentration risk, percentage	26.00%	26.00%
Commercial [Member] \| Federal National Mortgage Association [Member] \| Geographic Concentration Risk [Member] \| Mortgage Loans On Real Estate [Member] \| Texas [Member]
Investments [Line Items]
Concentration risk, percentage	9.00%	9.00%
Residential [Member]
Investments [Line Items]
Number of loans past due \| loan	63	65
Number of impaired loans \| loan	46	50
Impaired financing receivable, principal balance	$ 18.0	$ 22.0
Number Of Loans In Foreclosure \| loan	38	34
Mortgage Loans in Process of Foreclosure, Amount	$ 17.0	$ 15.0
Residential [Member] \| Federal National Mortgage Association [Member] \| Geographic Concentration Risk [Member] \| Mortgage Loans On Real Estate [Member] \| California [Member]
Investments [Line Items]
Concentration risk, percentage	21.00%	22.00%
Residential [Member] \| Federal National Mortgage Association [Member] \| Geographic Concentration Risk [Member] \| Mortgage Loans On Real Estate [Member] \| Florida [Member]
Investments [Line Items]
Concentration risk, percentage	12.00%	14.00%

Alternative investments as a percentage of overall invested assets.

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This item represents the change in gross unrealized holding gain or loss on available-for-sale securities that has been included in accumulated other comprehensive income, a separate component of shareholders' equity, during the period.

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Percentage of the fair value of portfolio that was rated investment grade as of balance sheet date.

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This item represents the percentage of the fair value of securities obtained as collateral under reverse repurchase agreements

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Financing receivable, Number of loans past due

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Impaired financing receivable, number of impaired loans

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This item represents total investment commitments as of the balance sheet date for fixed maturity available-for-sale securities, limited partnerships, real estate and mortgage loans on real estate.

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Investments [Line Items]

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Number Of Loans In Foreclosure

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No definition available.

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Number of partnerships represented in alternative investment portfolio.

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- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

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Fair value of collateral permitted, by contact or custom, to be sold or re-pledged.

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Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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