Cash Instruments - Fair Value, Cash Instruments, Measurement Inputs, Disclosure (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	$ 503,915	$ 526,687	$ 509,779
Loans and Securities Backed by Commercial Real Estate [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	2.80%	3.50%
Fair Value Unobservable Inputs, Recovery Rate	9.30%	19.60%
Fair Value Unobservable Inputs, Duration	9 months 18 days	3 months 18 days
Fair Value Unobservable Inputs, Basis (points)		(0.11%)
Loans and Securities Backed by Commercial Real Estate [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	23.00%	22.00%
Fair Value Unobservable Inputs, Recovery Rate	95.00%	96.50%
Fair Value Unobservable Inputs, Duration	6 years 3 months 18 days	5 years 3 months 18 days
Fair Value Unobservable Inputs, Basis (points)		0.04%
Loans and Securities Backed by Commercial Real Estate [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	12.10%	11.80%
Fair Value Unobservable Inputs, Recovery Rate	55.90%	59.40%
Fair Value Unobservable Inputs, Duration	2 years 6 months	2 years 3 months 18 days
Fair Value Unobservable Inputs, Basis (points)		(0.02%)
Loans and Securities Backed by Residential Real Estate [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	1.30%	3.20%
Fair Value Unobservable Inputs, Cumulative Loss Rate	14.70%	4.60%
Fair Value Unobservable Inputs, Duration	1 year 3 months 18 days	1 year 6 months
Loans and Securities Backed by Residential Real Estate [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	15.00%	17.00%
Fair Value Unobservable Inputs, Cumulative Loss Rate	50.40%	44.20%
Fair Value Unobservable Inputs, Duration	16 years 7 months 6 days	13 years 9 months 18 days
Loans and Securities Backed by Residential Real Estate [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	8.30%	7.90%
Fair Value Unobservable Inputs, Cumulative Loss Rate	28.80%	27.30%
Fair Value Unobservable Inputs, Duration	7 years 3 months 18 days	7 years
Bank Loans and Bridge Loans [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	2.10%	1.90%
Fair Value Unobservable Inputs, Recovery Rate	6.70%	14.50%
Fair Value Unobservable Inputs, Duration	9 months 18 days	8 months 12 days
Bank Loans and Bridge Loans [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	20.60%	36.60%
Fair Value Unobservable Inputs, Recovery Rate	85.30%	85.60%
Fair Value Unobservable Inputs, Duration	5 years 3 months 18 days	6 years 1 month 6 days
Bank Loans and Bridge Loans [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	9.10%	10.20%
Fair Value Unobservable Inputs, Recovery Rate	44.40%	51.20%
Fair Value Unobservable Inputs, Duration	2 years 6 months	2 years 2 months 12 days
Equities and Convertible Debentures [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Multiples	0.6	0.7
Fair Value Unobservable Inputs, Discount Rate/Yield	6.50%	7.10%
Fair Value Unobservable Inputs, Growth Rate		3.00%
Fair Value Unobservable Inputs, Capitalization Rates	5.00%	5.50%
Equities and Convertible Debentures [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Multiples	18.0	21.4
Fair Value Unobservable Inputs, Discount Rate/Yield	25.00%	20.00%
Fair Value Unobservable Inputs, Growth Rate		5.20%
Fair Value Unobservable Inputs, Capitalization Rates	12.00%	12.50%
Equities and Convertible Debentures [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Multiples	6.4	6.4
Fair Value Unobservable Inputs, Discount Rate/Yield	14.90%	14.80%
Fair Value Unobservable Inputs, Growth Rate		4.50%
Fair Value Unobservable Inputs, Capitalization Rates	7.10%	7.60%
Commercial Paper Certificates of Deposit Time Deposits and Other Money Market Instruments Corporate Debt Securities State and Municipal Foreign Government Debt Securities Other Debt Securities [Member] | Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	1.50%	0.90%
Fair Value Unobservable Inputs, Recovery Rate	0.00%	0.00%
Fair Value Unobservable Inputs, Duration	3 months 18 days	1 year 1 month 6 days
Commercial Paper Certificates of Deposit Time Deposits and Other Money Market Instruments Corporate Debt Securities State and Municipal Foreign Government Debt Securities Other Debt Securities [Member] | Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	18.00%	25.60%
Fair Value Unobservable Inputs, Recovery Rate	91.60%	70.00%
Fair Value Unobservable Inputs, Duration	13 years 4 months 24 days	11 years 4 months 24 days
Commercial Paper Certificates of Deposit Time Deposits and Other Money Market Instruments Corporate Debt Securities State and Municipal Foreign Government Debt Securities Other Debt Securities [Member] | Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value Unobservable Inputs, Yield	10.60%	10.90%
Fair Value Unobservable Inputs, Recovery Rate	63.10%	59.70%
Fair Value Unobservable Inputs, Duration	3 years 10 months 24 days	4 years 6 months
Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	$ 24,289	$ 24,046	$ 24,732
Level 3 [Member] | Loans and Securities Backed by Commercial Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	1,991	1,924
Level 3 [Member] | Loans and Securities Backed by Residential Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	995	1,765
Level 3 [Member] | Bank Loans and Bridge Loans [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	2,705	3,150
Level 3 [Member] | Equities and Convertible Debentures [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	9,377	8,549
Level 3 [Member] | Commercial Paper Certificates of Deposit Time Deposits and Other Money Market Instruments Corporate Debt Securities State and Municipal Foreign Government Debt Securities Other Debt Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total financial assets at fair value	$ 3,073	$ 2,743