Income Taxes - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Operating Loss Carryforwards [Line Items]
Net federal income tax liability, current	$ 23	$ 21
US Treasury Securities
Operating Loss Carryforwards [Line Items]
Debt securities	$ 870	$ 750

Amount, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity), and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Name:	us-gaap_DebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant