Investments, Investments on Deposit (Details) - USD ($) $ in Billions	Dec. 31, 2020	Dec. 31, 2019
Investments [Abstract]
Securities deposited by insurance subsidiaries under requirements of regulatory authorities and others	$ 3.0	$ 2.7
Cash and securities deposited with financial institutions in trust accounts or as collateral for letters of credit to secure obligations	$ 1.1	$ 1.1

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