Variable Interest Entities (Summary) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Variable Interest Entity [Line Items]
Assets	$ 146,330.6	$ 155,036.7
Liabilities	134,483.4	143,777.2
Other Assets
Variable Interest Entity [Line Items]
Total investment carrying amount	894.5	904.3
Other Assets | Affordable Housing
Variable Interest Entity [Line Items]
Total investment carrying amount	640.1	635.9
Other Assets | Other Community Development
Variable Interest Entity [Line Items]
Total investment carrying amount	254.4	268.4
Other Liabilities
Variable Interest Entity [Line Items]
Total unfunded commitments	205.5	218.9
Other Liabilities | Affordable Housing
Variable Interest Entity [Line Items]
Total unfunded commitments	205.5	218.9
Other Liabilities | Other Community Development
Variable Interest Entity [Line Items]
Total unfunded commitments	0.0	0.0
Variable Interest Entity, Not Primary Beneficiary | Other Assets
Variable Interest Entity [Line Items]
Assets	861.2	867.2
Variable Interest Entity, Not Primary Beneficiary | Other Liabilities
Variable Interest Entity [Line Items]
Liabilities	$ 198.5	$ 210.1