Fair Values - Breakdown of Loans and Lending Commitments at Fair Value and Unsettled Fair Value of Futures Contracts (Details) - Recurring - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Loans and lending commitments
Fair Value Measurements
Trading assets	$ 10,024	$ 10,925
Futures Contracts | Accounts Receivable and Other Receivables, Net
Fair Value Measurements
Derivative assets, unsettled fair value	501	615
Corporate | Loans and lending commitments
Fair Value Measurements
Trading assets	7,387	9,171
Residential real estate | Loans and lending commitments
Fair Value Measurements
Trading assets	1,206	1,153
Commercial real estate | Loans and lending commitments
Fair Value Measurements
Trading assets	$ 1,431	$ 601