Variable Interest Entities (Variable Interest Entity, Consolidated, Carrying Amount, Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Assets	$ 32,994,443	$ 30,389,344
Liabilities	29,774,753	27,181,574
Other Assets [Member] | Tax Credit - Finance Investments | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets	38,500	42,500
Accounts Payable and Accrued Liabilities [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Liabilities		15,100
Accounts Payable and Accrued Liabilities [Member] | Tax Credit - Finance Investments | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Liabilities	14,200
Other Investments [Member] | Other Non-Marketable Investments | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Assets	28,400	21,800
Unfunded Loan Commitment [Member] | Other Non-Marketable Investments | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	$ 70,500	$ 64,200