Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 172,291,100,000		$ 172,291,100,000		$ 170,003,900,000
Liabilities	160,468,100,000		160,468,100,000		158,315,600,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	0		0
Affordable housing tax credits and other tax benefits	23,100,000	$ 22,400,000	46,100,000	$ 38,700,000
Investment company, voluntary fee waived	79,200,000	$ 300,000	130,000,000.0	$ 300,000
Contractual obligation to provide financial support	0		0
Other Assets
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, assets	903,800,000		903,800,000		919,600,000
Other Assets | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	860,000,000.0		860,000,000.0		874,000,000.0
Other Liabilities
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, liabilities	266,300,000		266,300,000		351,600,000
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Liabilities	$ 250,500,000		$ 250,500,000		$ 335,900,000