Derivative Instruments and Hedging Activities (Credit Derivatives and Other Credit Contracts) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Protection Sold
Credit Derivatives
Notional	$ 249,199	$ 290,021
Fair value (asset)/liability	(1,567)	(1,944)
Protection Sold | Less than 1 (Year)
Credit Derivatives
Notional	81,715	88,228
Protection Sold | 1 - 3 (Years)
Credit Derivatives
Notional	69,988	81,673
Protection Sold | 3 - 5 (Years)
Credit Derivatives
Notional	58,118	94,110
Protection Sold | Over 5 (Years)
Credit Derivatives
Notional	39,378	26,010
Protection Sold | CDSs
Credit Derivatives
Notional	249,070	289,885
Fair value (asset)/liability	(1,587)	(1,960)
Protection Sold | CDSs | Less than 1 (Year)
Credit Derivatives
Notional	81,715	88,226
Protection Sold | CDSs | 1 - 3 (Years)
Credit Derivatives
Notional	69,986	81,673
Protection Sold | CDSs | 3 - 5 (Years)
Credit Derivatives
Notional	58,118	94,110
Protection Sold | CDSs | Over 5 (Years)
Credit Derivatives
Notional	39,251	25,876
Protection Sold | Single Name CDSs
Credit Derivatives
Notional	133,209	146,948
Fair value (asset)/liability	(1,148)	(1,277)
Protection Sold | Single Name CDSs | Investment Grade
Credit Derivatives
Notional	97,538	109,341
Fair value (asset)/liability	(1,124)	(1,167)
Protection Sold | Single Name CDSs | Non-investment Grade
Credit Derivatives
Notional	35,671	37,607
Fair value (asset)/liability	(24)	(110)
Protection Sold | Single Name CDSs | Less than 1 (Year)
Credit Derivatives
Notional	46,326	53,934
Protection Sold | Single Name CDSs | Less than 1 (Year) | Investment Grade
Credit Derivatives
Notional	33,332	39,721
Protection Sold | Single Name CDSs | Less than 1 (Year) | Non-investment Grade
Credit Derivatives
Notional	12,994	14,213
Protection Sold | Single Name CDSs | 1 - 3 (Years)
Credit Derivatives
Notional	49,798	58,884
Protection Sold | Single Name CDSs | 1 - 3 (Years) | Investment Grade
Credit Derivatives
Notional	35,927	42,591
Protection Sold | Single Name CDSs | 1 - 3 (Years) | Non-investment Grade
Credit Derivatives
Notional	13,871	16,293
Protection Sold | Single Name CDSs | 3 - 5 (Years)
Credit Derivatives
Notional	24,434	24,350
Protection Sold | Single Name CDSs | 3 - 5 (Years) | Investment Grade
Credit Derivatives
Notional	17,621	18,157
Protection Sold | Single Name CDSs | 3 - 5 (Years) | Non-investment Grade
Credit Derivatives
Notional	6,813	6,193
Protection Sold | Single Name CDSs | Over 5 (Years)
Credit Derivatives
Notional	12,651	9,780
Protection Sold | Single Name CDSs | Over 5 (Years) | Investment Grade
Credit Derivatives
Notional	10,658	8,872
Protection Sold | Single Name CDSs | Over 5 (Years) | Non-investment Grade
Credit Derivatives
Notional	1,993	908
Protection Sold | Total Index and Basket CDSs
Credit Derivatives
Notional	115,861	142,937
Fair value (asset)/liability	(439)	(683)
Protection Sold | Total Index and Basket CDSs | Investment Grade
Credit Derivatives
Notional	70,402	88,614
Fair value (asset)/liability	(811)	(1,091)
Protection Sold | Total Index and Basket CDSs | Non-investment Grade
Credit Derivatives
Notional	45,459	54,323
Fair value (asset)/liability	372	408
Protection Sold | Total Index and Basket CDSs | Less than 1 (Year)
Credit Derivatives
Notional	35,389	34,292
Protection Sold | Total Index and Basket CDSs | Less than 1 (Year) | Investment Grade
Credit Derivatives
Notional	29,448	29,046
Protection Sold | Total Index and Basket CDSs | Less than 1 (Year) | Non-investment Grade
Credit Derivatives
Notional	5,941	5,246
Protection Sold | Total Index and Basket CDSs | 1 - 3 (Years)
Credit Derivatives
Notional	20,188	22,789
Protection Sold | Total Index and Basket CDSs | 1 - 3 (Years) | Investment Grade
Credit Derivatives
Notional	14,049	15,418
Protection Sold | Total Index and Basket CDSs | 1 - 3 (Years) | Non-investment Grade
Credit Derivatives
Notional	6,139	7,371
Protection Sold | Total Index and Basket CDSs | 3 - 5 (Years)
Credit Derivatives
Notional	33,684	69,760
Protection Sold | Total Index and Basket CDSs | 3 - 5 (Years) | Investment Grade
Credit Derivatives
Notional	16,003	37,343
Protection Sold | Total Index and Basket CDSs | 3 - 5 (Years) | Non-investment Grade
Credit Derivatives
Notional	17,681	32,417
Protection Sold | Total Index and Basket CDSs | Over 5 (Years)
Credit Derivatives
Notional	26,600	16,096
Protection Sold | Total Index and Basket CDSs | Over 5 (Years) | Investment Grade
Credit Derivatives
Notional	10,902	6,807
Protection Sold | Total Index and Basket CDSs | Over 5 (Years) | Non-investment Grade
Credit Derivatives
Notional	15,698	9,289
Protection Sold | Index and Basket CDSs
Credit Derivatives
Notional	103,531	131,073
Fair value (asset)/liability	(163)	(341)
Protection Sold | Tranched Index and Basket
Credit Derivatives
Notional	12,330	11,864
Fair value (asset)/liability	(276)	(342)
Protection Sold | Single Name, and Non-tranched Index and Basket With Identical Underlying Reference Obligations
Credit Derivatives
Notional	233,572	274,473
Protection Sold | Other Credit Contracts
Credit Derivatives
Notional	129	136
Fair value (asset)/liability	20	16
Protection Sold | Other Credit Contracts | Less than 1 (Year)
Credit Derivatives
Notional	0	2
Protection Sold | Other Credit Contracts | 1 - 3 (Years)
Credit Derivatives
Notional	2	0
Protection Sold | Other Credit Contracts | 3 - 5 (Years)
Credit Derivatives
Notional	0	0
Protection Sold | Other Credit Contracts | Over 5 (Years)
Credit Derivatives
Notional	127	134
Protection Purchased | CDSs
Credit Derivatives
Notional	276,774	309,619
Fair value (asset)/liability	2,102	2,483
Protection Purchased | Single Name CDSs
Credit Derivatives
Notional	152,446	164,773
Fair value (asset)/liability	1,580	1,658
Protection Purchased | Index and Basket CDSs
Credit Derivatives
Notional	98,822	120,348
Fair value (asset)/liability	5	209
Protection Purchased | Tranched Index and Basket
Credit Derivatives
Notional	25,506	24,498
Fair value (asset)/liability	517	616
Protection Purchased | Single Name, and Non-tranched Index and Basket With Identical Underlying Reference Obligations
Credit Derivatives
Notional	$ 250,376	$ 281,162