Financial Instruments Subject to Off-Balance Sheet Credit Risk (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Resale agreements
Gross Assets	$ 14,904	$ 9,028
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts Presented in the Consolidated Balance Sheets	14,904	9,028
Counterparty Offsetting	0	0
Collateral	(14,904)	(9,028)
Net Amount	0	0
Securities borrowed
Gross Assets	873	735
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts Presented in the Consolidated Balance Sheets	873	735
Counterparty Offsetting	(673)	(730)
Collateral	(195)	(5)
Net Amount	5	0
Total Gross Assets	15,777	9,763
Total Assets, Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Total Assets, Net Amounts Presented in the Condensed Consolidated Balance Sheets	15,777	9,763
Total Assets, Gross Amounts Not Offset in the Consolidated Balance Sheet, Counterparty Offsetting	(673)	(730)
Total Assets, Gross Amounts Not Offset in the Consolidated Balance Sheet, Collateral	(15,099)	(9,033)
Total Assets, Net Amount	5	0
Securities loaned
Gross Liabilities	7,549	1,251
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts Presented in the Consolidated Balance Sheets	7,549	1,251
Counterparty Offsetting	(673)	(730)
Collateral	(6,049)	(445)
Net Amount	827	76
Total Gross Liabilities	7,549	1,251
Total Liabilities, Net Amounts Presented in the Consolidated Balance Sheet	7,549	1,251
Total Liabilities, Gross Amounts Not Offset in the Consolidated Balance Sheet, Counterparty Offsetting	(673)	(730)
Total Liabilities, Gross Amounts Not Offset in the Consolidated Balance Sheet, Collateral	(6,049)	(445)
Total Liabilities, Net Amount	827	76
Offsetting Assets [Line Items]
Fair value of client securities available to be pledged	84,006	26,685
Resale And Repurchase Agreements [Member]
Offsetting Assets [Line Items]
Fair value of client securities available to be pledged	$ 15,200	$ 9,200