Long-Term Debt and Shareholders' Equity (Long-term Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt And Equity [Abstract]
Subordinated notes	$ 540	$ 538
Finance lease obligations	4	4
Total	$ 544	$ 542

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant