Derivative Instruments and Hedging Activities - Maximum Potential Payout/Notional of Credit Protection Sold (Details) - Credit Protection Sold - USD ($) $ in Billions	Sep. 30, 2019	Dec. 31, 2018
Credit Derivatives
Maximum potential payout/notional	$ 229	$ 224
Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	34	42
1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	40	51
3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	95	102
Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	60	29
CDS
Credit Derivatives
Maximum potential payout/notional	229	224
CDS protection sold with identical protection purchased	219	210
CDS | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	34	42
CDS | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	40	51
CDS | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	95	102
CDS | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	60	29
Single-name CDS
Credit Derivatives
Maximum potential payout/notional	110	104
Single-name CDS | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	24	32
Single-name CDS | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	27	35
Single-name CDS | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	38	28
Single-name CDS | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	21	9
Single-name CDS | Investment grade
Credit Derivatives
Maximum potential payout/notional	76	73
Single-name CDS | Investment grade | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	16	22
Single-name CDS | Investment grade | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	18	24
Single-name CDS | Investment grade | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	26	19
Single-name CDS | Investment grade | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	16	8
Single-name CDS | Non-investment grade
Credit Derivatives
Maximum potential payout/notional	34	31
Single-name CDS | Non-investment grade | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	8	10
Single-name CDS | Non-investment grade | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	9	11
Single-name CDS | Non-investment grade | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	12	9
Single-name CDS | Non-investment grade | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	5	1
Index and basket CDS
Credit Derivatives
Maximum potential payout/notional	119	120
Index and basket CDS | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	10	10
Index and basket CDS | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	13	16
Index and basket CDS | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	57	74
Index and basket CDS | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	39	20
Index and basket CDS | Investment grade
Credit Derivatives
Maximum potential payout/notional	77	83
Index and basket CDS | Investment grade | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	5	5
Index and basket CDS | Investment grade | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	10	10
Index and basket CDS | Investment grade | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	40	61
Index and basket CDS | Investment grade | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	22	7
Index and basket CDS | Non-investment grade
Credit Derivatives
Maximum potential payout/notional	42	37
Index and basket CDS | Non-investment grade | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	5	5
Index and basket CDS | Non-investment grade | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	3	6
Index and basket CDS | Non-investment grade | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	17	13
Index and basket CDS | Non-investment grade | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	17	13
Other credit contracts
Credit Derivatives
Maximum potential payout/notional	0	0
Other credit contracts | Less Than 1 (Year)
Credit Derivatives
Maximum potential payout/notional	0	0
Other credit contracts | 1 - 3 (Years)
Credit Derivatives
Maximum potential payout/notional	0	0
Other credit contracts | 3 - 5 (Years)
Credit Derivatives
Maximum potential payout/notional	0	0
Other credit contracts | Over 5 (Years)
Credit Derivatives
Maximum potential payout/notional	$ 0	$ 0