Cash Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	$ 618,804	$ 643,833	$ 638,513
Level 3 [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	42,824	46,023	47,095
Level 3 [Member] | Loans and securities backed by commercial real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	2,969		3,389
Level 3 [Member] | Loans and securities backed by residential real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	1,738		1,619
Level 3 [Member] | Bank loans and bridge loans [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	9,997		11,235
Level 3 [Member] | Corporate Debt Securities, State and Municipal Obligations, Non-U.S. government and agency obligations, Other Debt Obligations [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	3,780		4,651
Level 3 [Member] | Equities and convertible debentures [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Total financial assets at fair value	$ 15,417		$ 14,855
Minimum [Member] | Loans and securities backed by commercial real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	3.90%		4.00%
Fair Value Unobservable Inputs, Recovery Rate	37.00%		37.00%
Fair Value Unobservable Inputs, Duration	0.5		0.1
Fair Value Unobservable Inputs, Basis	(18) points		(13) points
Minimum [Member] | Loans and securities backed by residential real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	3.00%		3.10%
Fair Value Unobservable Inputs, Cumulative Loss Rate	0.00%		0.00%
Fair Value Unobservable Inputs, Duration	0.5		1.3
Minimum [Member] | Bank loans and bridge loans [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	0.20%		0.30%
Fair Value Unobservable Inputs, Recovery Rate	30.00%		16.50%
Fair Value Unobservable Inputs, Duration	0.3		0.2
Minimum [Member] | Corporate Debt Securities, State and Municipal Obligations, Non-U.S. government and agency obligations, Other Debt Obligations [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	1.10%		0.60%
Fair Value Unobservable Inputs, Recovery Rate	0.00%		0.00%
Fair Value Unobservable Inputs, Duration	0.6		0.5
Minimum [Member] | Equities and convertible debentures [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Multiples	0.7		0.7
Fair Value Unobservable Inputs, Discount Rate/Yield	10.00%		10.00%
Fair Value Unobservable Inputs, Long-term Growth Rate And Compound Annual Growth Rate	1.20%		0.70%
Fair Value Unobservable Inputs, Capitalization Rates	4.70%		3.90%
Maximum [Member] | Loans and securities backed by commercial real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	16.80%		43.30%
Fair Value Unobservable Inputs, Recovery Rate	90.00%		96.20%
Fair Value Unobservable Inputs, Duration	5.8		7.0
Fair Value Unobservable Inputs, Basis	19 points		18 points
Maximum [Member] | Loans and securities backed by residential real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	16.80%		17.00%
Fair Value Unobservable Inputs, Cumulative Loss Rate	55.80%		61.60%
Fair Value Unobservable Inputs, Duration	11.2		5.9
Maximum [Member] | Bank loans and bridge loans [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	38.00%		34.50%
Fair Value Unobservable Inputs, Recovery Rate	85.00%		85.00%
Fair Value Unobservable Inputs, Duration	5.6		4.4
Maximum [Member] | Corporate Debt Securities, State and Municipal Obligations, Non-U.S. government and agency obligations, Other Debt Obligations [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	34.90%		33.70%
Fair Value Unobservable Inputs, Recovery Rate	70.00%		70.00%
Fair Value Unobservable Inputs, Duration	11.0		15.5
Maximum [Member] | Equities and convertible debentures [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Multiples	22.3		21.0
Fair Value Unobservable Inputs, Discount Rate/Yield	40.00%		25.00%
Fair Value Unobservable Inputs, Long-term Growth Rate And Compound Annual Growth Rate	21.00%		25.00%
Fair Value Unobservable Inputs, Capitalization Rates	11.30%		11.40%
Weighted Average [Member] | Loans and securities backed by commercial real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	8.40%		9.80%
Fair Value Unobservable Inputs, Recovery Rate	69.70%		81.70%
Fair Value Unobservable Inputs, Duration	2.3		2.6
Fair Value Unobservable Inputs, Basis	3 points		2 points
Weighted Average [Member] | Loans and securities backed by residential real estate [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	8.30%		9.70%
Fair Value Unobservable Inputs, Cumulative Loss Rate	18.90%		31.60%
Fair Value Unobservable Inputs, Duration	3.4		3.7
Weighted Average [Member] | Bank loans and bridge loans [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	9.30%		8.30%
Fair Value Unobservable Inputs, Recovery Rate	54.30%		56.00%
Fair Value Unobservable Inputs, Duration	2.4		1.9
Weighted Average [Member] | Corporate Debt Securities, State and Municipal Obligations, Non-U.S. government and agency obligations, Other Debt Obligations [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Yield	8.90%		8.60%
Fair Value Unobservable Inputs, Recovery Rate	63.20%		53.40%
Fair Value Unobservable Inputs, Duration	4.1		4.0
Weighted Average [Member] | Equities and convertible debentures [Member]
Fair Value, Cash Instruments, Unobservable Inputs
Fair Value Unobservable Inputs, Multiples	6.8		7.2
Fair Value Unobservable Inputs, Discount Rate/Yield	14.60%		14.30%
Fair Value Unobservable Inputs, Long-term Growth Rate And Compound Annual Growth Rate	10.50%		9.30%
Fair Value Unobservable Inputs, Capitalization Rates	7.30%		7.30%