Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Variable Interest Entity [Line Items]
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0		$ 0
Affordable housing tax credits and other tax benefits	12,500,000	$ 12,500,000	38,300,000	$ 36,500,000
Leveraged Leasing Transactions
Variable Interest Entity [Line Items]
VIE carrying amounts	134,900,000		134,900,000		$ 183,500,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0		$ 0
Leveraged Leasing Transactions | Lower Limit
Variable Interest Entity [Line Items]
Funding of assets cost via equity interest	20.00%		20.00%
Funding of asset's cost via third party non recourse debt holders	70.00%		70.00%
Leveraged Leasing Transactions | Upper Limit
Variable Interest Entity [Line Items]
Funding of assets cost via equity interest	30.00%		30.00%
Funding of asset's cost via third party non recourse debt holders	80.00%		80.00%
Accounting Standards Update 2015-02
Variable Interest Entity [Line Items]
Money market mutual funds fees waived	$ 300,000	$ 200,000	$ 700,000	$ 8,100,000
Other Assets
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, assets	333,800,000		333,800,000		218,900,000
Other Assets | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
VIE carrying amounts	303,600,000		303,600,000		186,500,000
Other Liabilities
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, liabilities	164,900,000		164,900,000		82,900,000
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities	$ 140,900,000		$ 140,900,000		$ 56,700,000