Collateral and Offsetting of Assets and Liabilities - Collateral in the Form of Securities Pledged (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	$ 7,450	$ 13,131
Derivatives
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	2,609	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	2,665	9,346
Other
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	2,176	329
Cash and Cash Equivalents
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	550
Cash and Cash Equivalents | Derivatives
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	0
Cash and Cash Equivalents | 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	550
Cash and Cash Equivalents | Other
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	0
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	782	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	602	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	180	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	613
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	613
Trading securities
Collateral in the Form of Securities Pledged [Line Items]
Securities pledged with the ability for the secured party to repledge	5,505	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	2,007	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	2,115	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	$ 1,383	$ 49