Variable Interest Entities (Variable Interest Entity, Consolidated, Carrying Amount, Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 31,654,874	$ 30,389,344
Liabilities	28,564,632	27,181,574
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Assets [Member] | Tax Credit - Finance Investments
Variable Interest Entity [Line Items]
Assets	41,200	42,500
Variable Interest Entity, Not Primary Beneficiary [Member] | Accounts Payable and Accrued Liabilities [Member] | Tax Credit - Finance Investments
Variable Interest Entity [Line Items]
Liabilities	15,100
Variable Interest Entity, Not Primary Beneficiary [Member] | Other Investments [Member] | Other Non-Marketable Investments
Variable Interest Entity [Line Items]
Assets	23,700	21,800
Unfunded Loan Commitment [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Other Non-Marketable Investments
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 70,200	$ 64,200