Loans and Allowance for Credit Losses - Amortized Cost Basis (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 4,560,000
2019	2,348,000
2018	1,992,000
2017	1,330,000
2016	496,000
Prior	93,000
Revolving Loans	16,216,000
Loans, gross	27,035,000	$ 26,309,000
Interest income	111,000
Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	21,850,000	21,267,000
Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	5,000,000	5,008,000
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	126,000	25,000
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	35,000	9,000
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	24,000
Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	19,952,000	20,528,000
Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	7,083,000	5,781,000
Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	25,091,000	24,543,000
Commercial and Financial Segment | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	20,095,000	19,501,000
Commercial and Financial Segment | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	4,811,000	5,008,000
Commercial and Financial Segment | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	126,000	25,000
Commercial and Financial Segment | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	35,000	9,000
Commercial and Financial Segment | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	24,000
Commercial and Financial Segment | Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,597,000
2019	1,398,000
2018	941,000
2017	874,000
2016	273,000
Prior	0
Revolving Loans	11,925,000
Loans, gross	18,008,000
Commercial and Financial Segment | Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,206,000
2019	420,000
2018	5,000
2017	141,000
2016	200,000
Prior	0
Revolving Loans	11,388,000
Loans, gross	14,360,000
Commercial and Financial Segment | Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
2020	391,000
2019	943,000
2018	877,000
2017	694,000
2016	43,000
Prior	0
Revolving Loans	537,000
Loans, gross	3,485,000
Commercial and Financial Segment | Domestic | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	28,000
2018	59,000
2017	39,000
2016	0
Prior	0
Revolving Loans	0
Loans, gross	126,000
Commercial and Financial Segment | Domestic | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5,000
2018	0
2017	0
2016	30,000
Prior	0
Revolving Loans	0
Loans, gross	35,000
Commercial and Financial Segment | Domestic | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	2,000
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Loans, gross	2,000
Commercial and Financial Segment | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,785,000
2019	401,000
2018	337,000
2017	179,000
2016	26,000
Prior	64,000
Revolving Loans	4,291,000
Loans, gross	7,083,000
Commercial and Financial Segment | Non-U.S. | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,527,000
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	4,208,000
Loans, gross	5,735,000
Commercial and Financial Segment | Non-U.S. | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
2020	258,000
2019	401,000
2018	337,000
2017	157,000
2016	26,000
Prior	64,000
Revolving Loans	83,000
Loans, gross	1,326,000
Commercial and Financial Segment | Non-U.S. | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	22,000
2016	0
Prior	0
Revolving Loans	0
Loans, gross	22,000
Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,944,000	1,766,000
Commercial real estate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	1,755,000	1,766,000
Commercial real estate | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	189,000	0
Commercial real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0	0
Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, gross	0
Commercial real estate | Domestic
Financing Receivable, Credit Quality Indicator [Line Items]
2020	178,000
2019	549,000
2018	714,000
2017	277,000
2016	197,000
Prior	29,000
Revolving Loans	0
Loans, gross	1,944,000	$ 1,766,000
Commercial real estate | Domestic | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	178,000
2019	417,000
2018	657,000
2017	277,000
2016	197,000
Prior	29,000
Revolving Loans	0
Loans, gross	1,755,000
Commercial real estate | Domestic | Speculative
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	132,000
2018	57,000
2017	0
2016	0
Prior	0
Revolving Loans	0
Loans, gross	189,000
Off Balance Sheet Commitment and Guarantees
Financing Receivable, Credit Quality Indicator [Line Items]
2020	379,052,000
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	36,976,000
Loans, gross	416,028,000
Financing Receivables and Off Balance Sheet Commitments
Financing Receivable, Credit Quality Indicator [Line Items]
2020	383,612,000
2019	2,348,000
2018	1,992,000
2017	1,330,000
2016	496,000
Prior	93,000
Revolving Loans	53,192,000
Loans, gross	443,063,000
Unfunded Loan Commitment | Off Balance Sheet Commitment and Guarantees
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	33,736,000
Loans, gross	33,736,000
Indemnified Securities Financing | Off Balance Sheet Commitment and Guarantees
Financing Receivable, Credit Quality Indicator [Line Items]
2020	379,052,000
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	0
Loans, gross	379,052,000
Standby Letters of Credit | Off Balance Sheet Commitment and Guarantees
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans	3,240,000
Loans, gross	$ 3,240,000