Bank Loans and Related Allowance for Credit Losses (Nonperforming Assets and Troubled Debt Restructuring) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	$ 28,908	$ 23,843
Troubled debt restructurings	0	1
Total nonperforming assets and troubled debt restructurings	54	91
Nonperforming Financial Instruments [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	54	90
Nonperforming Financial Instruments [Member] | Nonaccrual Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	53	89
Nonperforming Financial Instruments [Member] | Other Real Estate Owned [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total nonperforming assets	$ 1	$ 1