Variable Interest Entities (Summary) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Variable Interest Entity [Line Items]
Assets	$ 150,783.1	$ 155,036.7	$ 183,889.8
Liabilities	138,885.2	143,777.2
Other Assets
Variable Interest Entity [Line Items]
Investment Carrying Amount	889.1	904.3
Other Assets | Affordable Housing
Variable Interest Entity [Line Items]
Investment Carrying Amount	622.8	635.9
Other Assets | Other Community Development
Variable Interest Entity [Line Items]
Investment Carrying Amount	266.3	268.4
Other Liabilities
Variable Interest Entity [Line Items]
Unfunded Commitments	178.8	218.9
Other Liabilities | Affordable Housing
Variable Interest Entity [Line Items]
Unfunded Commitments	178.8	218.9
Other Liabilities | Other Community Development
Variable Interest Entity [Line Items]
Unfunded Commitments	0.0	0.0
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	857.0	867.2
Liabilities	$ 172.0	$ 210.1