Cash Instruments (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Commercial paper, certificates of deposit, time deposits and other money market instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance		$ 8		$ 0
Net Realized Gains / (Losses)		0		0
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End		0		0
Purchases		0		8
Sales		(1)		(1)
Settlements		0		0
Transfers Into Level 3		0		0
Transfers Out Of Level 3		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance		7		7
Non-U.S. government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	47	105	26	148
Net Realized Gains / (Losses)	2	(4)	3	(56)
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	3	(1)	6	1
Purchases	42	0	64	0
Sales	(95)	(20)	(9)	(16)
Settlements	0	(70)	(2)	(70)
Transfers Into Level 3	92	0	5	5
Transfers Out Of Level 3	(1)	(2)	(3)	(4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	90	8	90	8
Loans and securities backed by commercial real estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	3,164	3,156	3,389	3,346
Net Realized Gains / (Losses)	44	70	60	121
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	75	46	132	116
Purchases	216	502	391	829
Sales	(431)	(494)	(569)	(1,007)
Settlements	(258)	(274)	(624)	(517)
Transfers Into Level 3	305	233	385	359
Transfers Out Of Level 3	(146)	(73)	(195)	(81)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	2,969	3,166	2,969	3,166
Loans and securities backed by residential real estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	1,683	1,610	1,619	1,709
Net Realized Gains / (Losses)	30	79	65	109
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	61	28	79	63
Purchases	223	301	475	514
Sales	(163)	(237)	(365)	(406)
Settlements	(156)	(254)	(182)	(390)
Transfers Into Level 3	106	119	124	59
Transfers Out Of Level 3	(46)	(14)	(77)	(26)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	1,738	1,632	1,738	1,632
Bank loans and bridge loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	11,688	11,051	11,235	11,285
Net Realized Gains / (Losses)	160	122	289	334
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	180	20	220	77
Purchases	1,530	1,685	2,669	2,153
Sales	(1,217)	(1,113)	(1,163)	(2,235)
Settlements	(1,780)	(1,035)	(3,007)	(1,409)
Transfers Into Level 3	518	691	969	1,297
Transfers Out Of Level 3	(1,082)	(960)	(1,215)	(1,041)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	9,997	10,461	9,997	10,461
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	2,442	2,512	2,821	2,480
Net Realized Gains / (Losses)	63	83	187	175
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	58	(28)	347	89
Purchases	365	453	502	658
Sales	(364)	(397)	(1,183)	(662)
Settlements	(90)	(177)	(290)	(325)
Transfers Into Level 3	187	135	268	267
Transfers Out Of Level 3	(169)	(214)	(160)	(315)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	2,492	2,367	2,492	2,367
State and municipal obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	334	612	619	599
Net Realized Gains / (Losses)	2	4	6	10
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	3	5	4	5
Purchases	58	13	118	20
Sales	(162)	(67)	(421)	(65)
Settlements	0	(3)	(2)	(10)
Transfers Into Level 3	93	5	6	6
Transfers Out Of Level 3	(6)	(22)	(8)	(18)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	322	547	322	547
Other debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	855	1,549	1,185	1,451
Net Realized Gains / (Losses)	9	13	22	69
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	(3)	18	18	30
Purchases	183	423	423	445
Sales	(92)	(214)	(390)	(283)
Settlements	(132)	(43)	(104)	(78)
Transfers Into Level 3	260	17	160	127
Transfers Out Of Level 3	(204)	(6)	(438)	(4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	876	1,757	876	1,757
Equities and convertible debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	15,224	14,874	14,855	13,667
Net Realized Gains / (Losses)	42	(4)	86	27
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	346	357	920	644
Purchases	740	792	968	1,410
Sales	(178)	(182)	(491)	(219)
Settlements	(330)	(408)	(916)	(587)
Transfers Into Level 3	349	272	1,097	842
Transfers Out Of Level 3	(776)	(1,281)	(1,102)	(1,364)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	15,417	14,420	15,417	14,420
Cash Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	35,437	35,477	35,749	34,685
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	441	747	642	905
Net Realized Gains / (Losses)	352	363	718	789
Net Realized (Gains) / Losses	14	5	47	(22)
Net Unrealized Gains / (Losses) Relating to Instruments Still Held at Period-End	723	445	1,726	1,025
Net Unrealized (Gains) / Losses Relating to Instruments Still Held at Period-End	0	37	0	(2)
Purchases	3,357	4,169	5,610	6,037
Sales	(2,702)	(2,725)	(4,591)	(4,894)
Settlements	(2,746)	(2,264)	(5,127)	(3,386)
Purchases	(210)	(151)	(423)	(311)
Sales	89	51	172	100
Settlements	3	103	7	141
Transfers Into Level 3	1,910	1,472	3,014	2,962
Transfers Into Level 3	75	46	64	118
Transfers Out Of Level 3	(2,430)	(2,572)	(3,198)	(2,853)
Transfers Out Of Level 3	(27)	(99)	(124)	(190)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	33,901	34,365	33,901	34,365
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	$ 385	$ 739	$ 385	$ 739