Fair Value Measurement - Transfers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total realized/unrealized gains/(losses)	$ 338	$ (615)	$ 130
Equity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total realized/unrealized gains/(losses)	198	(417)	(145)
Trading loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 3 into level 2, assets	765	1,491	787
Transfers from level 2 into level 3, assets	813	806	1,044
Total debt and equity instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities	36	9	7
Transfers from level 2 into level 3, liabilities	14	3	13
Long-term debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities	831	925	1,389
Transfers from level 2 into level 3, liabilities	1,143	1,660	315
Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 3 into level 2, assets	2,100
Recurring | Derivative receivables | Equity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 3 into level 2, assets	1,200
Transfers from level 2 into level 3, assets	1,000	1,000	1,100
Recurring | Trading loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 3 into level 2, assets	1,000
Transfers from level 2 into level 3, assets	1,100	1,700	1,000
Recurring | Total debt and equity instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities	1,500
Transfers from level 2 into level 3, liabilities	1,400
Recurring | Derivative payables | Equity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities	1,500	1,200
Transfers from level 2 into level 3, liabilities	1,600	2,500	1,000
Recurring | Long-term debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from level 3 into level 2, liabilities		1,500	$ 1,400
Recurring | Liability | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total realized/unrealized gains/(losses)	$ 1,600	$ (1,300)