Securities Financing Activities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Offsetting Assets [Line Items]
Securities Purchased under Agreements to Resell	$ 986	$ 143
Securities borrowed or purchased under resale agreements	1,417	143
Securities Borrowed	431	0
Offsetting Liabilities [Line Items]
Short-term borrowings	18,218	5,178
Securities Sold under Agreements to Repurchase
Offsetting Liabilities [Line Items]
Short-term borrowings	1,969	251
Securities Sold under Agreements to Repurchase | U.S. Treasury
Offsetting Liabilities [Line Items]
Short-term borrowings	150	2
Securities Sold under Agreements to Repurchase | US Government-sponsored Enterprises Debt Securities [Member]
Offsetting Liabilities [Line Items]
Short-term borrowings	124	53
Securities Sold under Agreements to Repurchase | Residential Mortgage Backed Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	1,069	196
Securities Sold under Agreements to Repurchase | Corporate Debt Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	626	0
Securities Sold under Agreements to Repurchase | Maturity Overnight
Offsetting Liabilities [Line Items]
Short-term borrowings	1,440	130
Securities Sold under Agreements to Repurchase | Maturity Overnight | U.S. Treasury
Offsetting Liabilities [Line Items]
Short-term borrowings	115	0
Securities Sold under Agreements to Repurchase | Maturity Overnight | US Government-sponsored Enterprises Debt Securities [Member]
Offsetting Liabilities [Line Items]
Short-term borrowings	87	27
Securities Sold under Agreements to Repurchase | Maturity Overnight | Residential Mortgage Backed Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	928	103
Securities Sold under Agreements to Repurchase | Maturity Overnight | Corporate Debt Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	310	0
Securities Sold under Agreements to Repurchase | Maturity Less than 30 Days
Offsetting Liabilities [Line Items]
Short-term borrowings	429	121
Securities Sold under Agreements to Repurchase | Maturity Less than 30 Days | U.S. Treasury
Offsetting Liabilities [Line Items]
Short-term borrowings	35	2
Securities Sold under Agreements to Repurchase | Maturity Less than 30 Days | US Government-sponsored Enterprises Debt Securities [Member]
Offsetting Liabilities [Line Items]
Short-term borrowings	37	26
Securities Sold under Agreements to Repurchase | Maturity Less than 30 Days | Residential Mortgage Backed Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	41	93
Securities Sold under Agreements to Repurchase | Maturity Less than 30 Days | Corporate Debt Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	316	$ 0
Securities Sold under Agreements to Repurchase | Maturity 30 to 90 Days
Offsetting Liabilities [Line Items]
Short-term borrowings	100
Securities Sold under Agreements to Repurchase | Maturity 30 to 90 Days | U.S. Treasury
Offsetting Liabilities [Line Items]
Short-term borrowings	0
Securities Sold under Agreements to Repurchase | Maturity 30 to 90 Days | US Government-sponsored Enterprises Debt Securities [Member]
Offsetting Liabilities [Line Items]
Short-term borrowings	0
Securities Sold under Agreements to Repurchase | Maturity 30 to 90 Days | Residential Mortgage Backed Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	100
Securities Sold under Agreements to Repurchase | Maturity 30 to 90 Days | Corporate Debt Securities
Offsetting Liabilities [Line Items]
Short-term borrowings	$ 0