Collateral and Offsetting of Assets and Liabilities - Collateral in the Form of Securities Pledged (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	$ 18,922	$ 13,131
Derivatives
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	4,412	3,456
Securities Sold under Agreements to Repurchase
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	13,912	9,346
Other
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	598	329
Debt securities of consolidated trusts
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	1,197	842
Debt securities of consolidated trusts | Derivatives
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	977	562
Debt securities of consolidated trusts | Securities Sold under Agreements to Repurchase
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	0	0
Debt securities of consolidated trusts | Other
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	220	280
Available-for-sale securities
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	7
Available-for-sale securities | Derivatives
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	0
Available-for-sale securities | Securities Sold under Agreements to Repurchase
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	0
Available-for-sale securities | Other
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	7
Trading securities
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	17,718	12,289
Trading securities | Derivatives
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	3,435	2,894
Trading securities | Securities Sold under Agreements to Repurchase
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	13,912	9,346
Trading securities | Other
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	$ 371	$ 49