Allowance for Credit Losses (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Time period used for projecting future conditions to estimate credit losses	2 years
Credit loss, excluding accrued interest, expense (reversal)	$ 10,700,000	$ (81,500,000)	$ 125,000,000.0
Credit loss expense (reversal) and available-for-sale, allowance for credit loss	12,000,000.0	(81,500,000)	125,000,000.0
Financing receivable, excluding accrued interest, allowance for credit loss, writeoff (recovery)	(4,200,000)	(6,300,000)	3,200,000
Other financial assets, allowance for credit loss, excluding accrued interest	800,000	1,000,000	$ 800,000	$ 0
Corporate Debt
Financing Receivable, Allowance for Credit Loss [Line Items]
Credit loss, excluding accrued interest, expense (reversal)	1,300,000	0
Other Financial Assets
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, accrued interest, writeoff	$ 0	$ 0