Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Variable Interest Entity [Line Items]
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0
Affordable housing tax credits and other tax benefits	16,400,000	$ 14,700,000
Fair value, investments, entities that calculate net asset value per Share, unfunded commitments	0		$ 0
Leveraged Leasing Transactions
Variable Interest Entity [Line Items]
VIE carrying amounts	56,600,000		56,800,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0
Leveraged Leasing Transactions | Lower Limit
Variable Interest Entity [Line Items]
Funding of assets cost via equity interest	20.00%
Funding of asset's cost via third party non recourse debt holders	70.00%
Leveraged Leasing Transactions | Upper Limit
Variable Interest Entity [Line Items]
Funding of assets cost via equity interest	30.00%
Funding of asset's cost via third party non recourse debt holders	80.00%
Other Assets
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, assets	$ 589,500,000		602,400,000
Alternative investment	25,000,000		29,200,000
Other Assets | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
VIE carrying amounts	537,800,000		549,800,000
Other Liabilities
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, liabilities	302,100,000		321,000,000
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Variable interest entity, nonconsolidated, carrying amount, liabilities	$ 263,600,000		$ 279,500,000