Fair Value Measurement - Transfers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nontrading loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, assets	$ 2,571	$ 188	$ 194
Transfers from Level 3 into level 2, assets	684	153	159
Total debt and equity instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	136	16	14
Transfers from level 3 into level 2, liabilities	8	47	36
Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	265	12	2
Transfers from level 3 into level 2, liabilities	943	1,209	540
Long-term debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	1,250	651	1,143
Transfers from level 3 into level 2, liabilities	1,282	1,448	831
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized/unrealized gains (losses), assets	10	(2,100)
Realized/unrealized gains (losses), liabilities	102	(3,300)	1,600
Recurring | Derivative receivables | Equity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, assets	2,600		1,000
Transfers from Level 3 into level 2, assets	2,400	1,100	1,200
Recurring | Nontrading loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, assets	2,600
Recurring | Total debt and equity instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	1,800	993	1,400
Transfers from level 3 into level 2, liabilities	2,000	1,500	1,500
Recurring | Derivative payables | Equity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	3,500	904	1,600
Transfers from level 3 into level 2, liabilities	2,400	1,300	1,500
Recurring | Derivative payables | Commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities		962
Recurring | Derivative payables | Interest rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	880
Recurring | Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities	943	1,200
Recurring | Long-term debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 2 into level 3, liabilities	1,200		$ 1,100
Transfers from level 3 into level 2, liabilities	$ 1,300	$ 1,400