Fair Value Measurements - Fair Value of Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	$ 811	$ 750	$ 965
Securities available for sale	14,376	13,360	12,245
Derivative asset netting adjustments	(945)	(1,034)	(613)
Total derivative assets	793	609	413
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liability netting adjustments	(566)	(542)	(393)
Total derivative liabilities	676	784	384
Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	12,003	11,270	10,009
States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	15	23	27
Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	28	32	32
Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	2,330	2,035	2,177
Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Commercial loans	9	2	1
Total trading account assets	811	750	965
Securities available for sale	14,376	13,360	12,245
Total other investments	350	420	485
Derivative assets	1,738	1,643	1,026
Derivative asset netting adjustments	(945)	(1,034)	(613)
Total derivative assets	793	609	413
Accrued income and other assets	2
Total assets at fair value	16,332	15,139	14,108
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	1,242	1,326	777
Derivative liability netting adjustments	(566)	(542)	(393)
Total derivative liabilities	676	784	384
Accrued expense and other liabilities	2
Total liabilities on a recurring basis at fair value	1,355	1,207	880
Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	12,003	11,270	10,009
Recurring [Member] | Trading Account Assets [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	802	748	964
Recurring [Member] | U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	694	555	596
Recurring [Member] | States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	35	38	24
Securities available for sale	15	23	27
Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	27	31	158
Securities available for sale	28	32	32
Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	66	104	115
Recurring [Member] | Principal Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	271	302	353
Recurring [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	4	4	4
Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	337	406	468
Recurring [Member] | Equity and Mezzanine Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	9	10	13
Recurring [Member] | Private Equity and Mezzanine Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	9	10	13
Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	46	124	186
Securities available for sale	2,330	2,035	2,177
Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	677	423	496
Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1,119	937	846
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	656	644	616
Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	130	93	81
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	112	81	64
Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	482	608	95
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	469	594	90
Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	7	5	4
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	5	7	7
Level 1 [Member] | Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account assets	4	2	13
Securities available for sale	11	22	22
Total other investments		2
Derivative assets	120	91	73
Total derivative assets	120	91	73
Total assets at fair value	135	117	108
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	102	77	55
Total derivative liabilities	102	77	55
Total liabilities on a recurring basis at fair value	102	77	61
Level 1 [Member] | Recurring [Member] | Trading Account Assets [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	4	2	13
Level 1 [Member] | Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	4	2	13
Securities available for sale	11	22	22
Level 1 [Member] | Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments		2
Level 1 [Member] | Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments		2
Level 1 [Member] | Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities			6
Level 1 [Member] | Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	120	91	73
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	102	77	55
Level 2 [Member] | Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Commercial loans	9	2	1
Total trading account assets	807	748	952
Securities available for sale	14,348	13,328	12,213
Derivative assets	1,593	1,536	931
Total derivative assets	1,593	1,536	931
Accrued income and other assets	2
Total assets at fair value	16,750	15,612	14,096
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	1,140	1,248	721
Total derivative liabilities	1,140	1,248	721
Accrued expense and other liabilities	2
Total liabilities on a recurring basis at fair value	1,819	1,671	1,211
Level 2 [Member] | Recurring [Member] | Collateralized Mortgage Obligations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	12,003	11,270	10,009
Level 2 [Member] | Recurring [Member] | Trading Account Assets [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	798	746	951
Level 2 [Member] | Recurring [Member] | U.S. Treasury, Agencies and Corporations [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	694	555	596
Level 2 [Member] | Recurring [Member] | States and Political Subdivisions [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	35	38	24
Securities available for sale	15	23	27
Level 2 [Member] | Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	23	29	145
Level 2 [Member] | Recurring [Member] | Other Mortgage-Backed Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total trading account securities	46	124	186
Securities available for sale	2,330	2,035	2,177
Level 2 [Member] | Recurring [Member] | Short Positions [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	677	423	490
Level 2 [Member] | Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	1,097	924	827
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	656	644	616
Level 2 [Member] | Recurring [Member] | Foreign Exchange [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	10	2	8
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	10	4	9
Level 2 [Member] | Recurring [Member] | Commodity [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	482	608	95
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	469	594	89
Level 2 [Member] | Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	4	2	1
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities	5	6	7
Level 3 [Member] | Recurring [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	17	10	10
Total other investments	350	418	485
Derivative assets	25	16	22
Total derivative assets	25	16	22
Total assets at fair value	392	444	517
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities		1	1
Total derivative liabilities		1	1
Total liabilities on a recurring basis at fair value		1	1
Level 3 [Member] | Recurring [Member] | Other Securities [Member]
ASSETS MEASURED ON A RECURRING BASIS
Securities available for sale	17	10	10
Level 3 [Member] | Recurring [Member] | Principal Investments Direct [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	66	102	115
Level 3 [Member] | Recurring [Member] | Principal Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	271	302	353
Level 3 [Member] | Recurring [Member] | Other [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	4	4	4
Level 3 [Member] | Recurring [Member] | Principal Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	337	404	468
Level 3 [Member] | Recurring [Member] | Equity and Mezzanine Investments Indirect [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	9	10	13
Level 3 [Member] | Recurring [Member] | Private Equity and Mezzanine Investments [Member]
ASSETS MEASURED ON A RECURRING BASIS
Total other investments	9	10	13
Level 3 [Member] | Recurring [Member] | Interest Rate [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	22	13	19
Level 3 [Member] | Recurring [Member] | Commodity [Member]
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities			1
Level 3 [Member] | Recurring [Member] | Credit [Member]
ASSETS MEASURED ON A RECURRING BASIS
Derivative assets	$ 3	3	$ 3
LIABILITIES MEASURED ON A RECURRING BASIS
Derivative liabilities		$ 1