Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 163,924,100,000		$ 170,003,900,000
Liabilities	152,466,200,000		158,315,600,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	0
Affordable housing tax credits and other tax benefits	23,000,000.0	$ 16,300,000
Investment company, voluntary fee waived	50,200,000	$ 0
Contractual obligation to provide financial support	0
Other Assets
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, assets	908,100,000		919,600,000
Other Assets | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	863,600,000		874,000,000.0
Other Liabilities
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, liabilities	313,700,000		351,600,000
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Liabilities	$ 298,300,000		$ 335,900,000