Commitments, Contingencies and Other Items (Narrative) (Details) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Commitments and Contingencies [Line Items]
Initial commitments	$ 2,700,000,000
Fulfilled commitments	1,300,000,000
Unfunded commitments	$ 1,400,000,000
Operating lease, weighted average lease term	4 years 8 months 12 days
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Other liabilities	Other liabilities
Operating lease, expense	$ 8,400,000	$ 9,800,000
Lessee, finance lease, term of contract	20 years
Lessee, finance lease, renewal term	30 years
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
Finance Lease, Liability, Statement of Financial Position [Extensible List]	Other liabilities	Other liabilities
Letter of Credit
Commitments and Contingencies [Line Items]
Letters of credit outstanding	$ 1,100,000,000
Letter of Credit \| Top Layer Reinsurance Ltd.
Commitments and Contingencies [Line Items]
Collateral pledged to support letter of credit	37,500,000
Letter of Credit \| Capital Support Agreement \| Top Layer Reinsurance Ltd.
Commitments and Contingencies [Line Items]
Maximum mandatory capital contribution in the event of loss that reduced capital and surplus below specified level	50,000,000
Other assets
Commitments and Contingencies [Line Items]
Operating lease, right-of-use asset	22,900,000	$ 29,800,000
Finance lease, right-of-use asset	28,000,000	18,000,000
Other liabilities
Commitments and Contingencies [Line Items]
Operating lease, liability	23,100,000	29,900,000
Finance lease, liability	22,500,000	22,900,000
Interest Expense
Commitments and Contingencies [Line Items]
Finance lease, interest expense	2,300,000	2,300,000
Other income (loss)
Commitments and Contingencies [Line Items]
Finance lease, right-of-use asset, amortization	$ 500,000	$ 500,000

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Private Equity Investments and Other Entities, Commitments Fulfilled

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Private Equity Investments and Other Entities, Initial Commitments

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Private Equity Investments and Other Entities, Unfunded Commitments

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Amount of interest expense on finance lease liability.

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Present value of lessee's discounted obligation for lease payments from finance lease.

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Term of lessee's finance lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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Amount of lessee's right to use underlying asset under operating lease.

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Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The carrying amount, as of the date of the latest financial statement presented, of all assets that are pledged as collateral for the payment of the related debt obligation primarily arising from secured borrowings, repurchase agreements or other current or potential obligations, where the secured party does not have the right by contract or custom to sell or re-pledge the collateral and therefore are not reclassified and separately reported in the statement of financial position.

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