Financial Instruments Subject to Off-Balance Sheet Credit Risk (Offsetting Assets and Liabilities) (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Resale agreements
Gross Assets	$ 13,625,000,000	$ 14,904,000,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Net Amounts Presented in the Condensed Consolidated Balance Sheets	13,625,000,000	14,904,000,000
Counterparty Offsetting	0	0
Collateral	(13,625,000,000)	(14,904,000,000)
Net Amount	0	0
Securities borrowed
Gross Assets	900,000,000	873,000,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Net Amounts Presented in the Condensed Consolidated Balance Sheets	900,000,000	873,000,000
Counterparty Offsetting	(459,000,000)	(673,000,000)
Collateral	(425,000,000)	(195,000,000)
Net Amount	16,000,000	5,000,000
Total Gross Assets	14,525,000,000	15,777,000,000
Total Assets, Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Total Assets, Net Amounts Presented in the Condensed Consolidated Balance Sheets	14,525,000,000	15,777,000,000
Total Assets, Gross Amounts Not Offset in the Consolidated Balance Sheet, Counterparty Offsetting	(459,000,000)	(673,000,000)
Total Assets, Gross Amounts Not Offset in the Consolidated Balance Sheet, Collateral	(14,050,000,000)	(15,099,000,000)
Total Assets, Net Amount	16,000,000	5,000,000
Securities loaned
Gross Liabilities	9,253,000,000	7,549,000,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Net Amounts Presented in the Condensed Consolidated Balance Sheets	9,253,000,000	7,549,000,000
Counterparty Offsetting	(459,000,000)	(673,000,000)
Collateral	(8,108,000,000)	(6,049,000,000)
Net Amount	686,000,000	827,000,000
Secured short-term borrowings
Gross Liabilities	1,500,000,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0
Net Amounts Presented in the Condensed Consolidated Balance Sheets	1,500,000,000
Counterparty Offsetting	0
Collateral	(1,500,000,000)
Net Amount	0
Total Gross Liabilities	10,753,000,000	7,549,000,000
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Total Liabilities, Net Amounts Presented in the Consolidated Balance Sheet	10,753,000,000	7,549,000,000
Total Liabilities, Gross Amounts Not Offset in the Consolidated Balance Sheet, Counterparty Offsetting	(459,000,000)	(673,000,000)
Total Liabilities, Gross Amounts Not Offset in the Consolidated Balance Sheet, Collateral	(9,608,000,000)	(6,049,000,000)
Total Liabilities, Net Amount	686,000,000	827,000,000
Offsetting Assets [Line Items]
Fair value of client securities available to be pledged	114,171,000,000	84,006,000,000
Resale And Repurchase Agreements [Member]
Offsetting Assets [Line Items]
Fair value of client securities available to be pledged	$ 13,900,000,000	$ 15,200,000,000