Investments - Investments on Deposit (Details) - USD ($) $ in Billions	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Securities deposited by insurance subsidiaries under requirements of regulatory authorities and others	$ 3.1	$ 2.8
Cash and securities deposited with financial institutions in trust accounts or as collateral for letters of credit to secure obligations	$ 0.9	$ 0.9

Cash and securities deposited in a special reserve account for the exclusive benefit of customers.

No definition available.

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