Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Other assets	$ 700.0	$ 597.0
Other liabilities	435.0	457.0
Related Party
Related Party Transaction [Line Items]
Management fee expense	1.9	2.0	$ 2.4
Accounts payable	$ 1.0	$ 1.0
Wellington Management Company LLP
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners	5.00%	5.00%
BlackRock Financial Management Inc.
Related Party Transaction [Line Items]
Ownership percentage by noncontrolling owners	5.00%	5.00%

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business.

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