Bank Loans and Related Allowance for Credit Losses (Nonperforming Assets and Troubled Debt Restructuring) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	$ 19,550	$ 18,230
Troubled debt restructurings	2	2
Total nonperforming assets and troubled debt restructurings	26	25
Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	24	23
Nonperforming Financial Instruments [Member] | Nonaccrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	23	22
Nonperforming Financial Instruments [Member] | Other Real Estate Owned [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	$ 1	$ 1