Variable Interest Entities (Summary) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Assets	$ 156,111.0	$ 150,783.1
Liabilities	144,009.2	138,885.2
Other Assets
Variable Interest Entity [Line Items]
Investment Carrying Amount	866.4	889.1
Other Assets | Affordable Housing
Variable Interest Entity [Line Items]
Investment Carrying Amount	603.3	622.8
Other Assets | New Markets
Variable Interest Entity [Line Items]
Investment Carrying Amount	263.1	266.3
Other Liabilities
Variable Interest Entity [Line Items]
Unfunded Commitments	163.3	178.8
Other Liabilities | Affordable Housing
Variable Interest Entity [Line Items]
Unfunded Commitments	163.3	178.8
Other Liabilities | New Markets
Variable Interest Entity [Line Items]
Unfunded Commitments	0.0	0.0
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	835.7	857.0
Liabilities	$ 156.6	$ 172.0