Securities-Maturity Distribution by Carrying Amount and Yield (on Tax Equivalent Basis) of Investment Securities Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Securities available-for-sale:
One year or less	$ 10,023
Over 1 through 5 years	29,326
Over 5 through 10 years	5,413
Over 10 years	4,458
Total	95,559
Securities held-to-maturity:
One year or less	154
Over 1 through 5 years	3,830
Over 5 through 10 years	1,500
Over 10 years	18
Held-to-maturity (fair value of $20,167 and $19,443)	20,137
Mortgage-backed securities
Securities available-for-sale:
Without single maturity date	40,432
Securities held-to-maturity:
Mortgage-backed securities	14,635
Asset-backed securities
Securities available-for-sale:
Without single maturity date	5,021
Equity securities
Securities available-for-sale:
Without single maturity date	886	[1]
U.S. Treasury
Securities available-for-sale:
One year or less	2,418
Over 1 through 5 years	13,176
Over 5 through 10 years	1,358
Over 10 years	4,149
Total	21,101
Securities held-to-maturity:
One year or less	150
Over 1 through 5 years	2,858
Over 5 through 10 years	1,158
Over 10 years	0
Held-to-maturity (fair value of $20,167 and $19,443)	4,166
Securities available-for-sale:
One year or less (percent)	0.21%	[2]
Over 1 through 5 years (percent)	0.86%	[2]
Over 5 through 10 years (percent)	2.83%	[2]
Over 10 years (percent)	3.12%	[2]
Total (percent)	1.35%	[2]
Securities held-to-maturity:
One year or less (percent)	0.28%	[2]
Over 1 through 5 years (percent)	1.27%	[2]
Over 5 through 10 years (percent)	2.21%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	1.49%	[2]
U.S. Government agencies
Securities available-for-sale:
One year or less	135
Over 1 through 5 years	137
Over 5 through 10 years	89
Over 10 years	0
Total	361
Securities held-to-maturity:
One year or less	0
Over 1 through 5 years	233
Over 5 through 10 years	111
Over 10 years	0
Held-to-maturity (fair value of $20,167 and $19,443)	344
Securities available-for-sale:
One year or less (percent)	1.75%	[2]
Over 1 through 5 years (percent)	2.09%	[2]
Over 5 through 10 years (percent)	1.52%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	1.82%	[2]
Securities held-to-maturity:
One year or less (percent)	0.00%	[2]
Over 1 through 5 years (percent)	1.03%	[2]
Over 5 through 10 years (percent)	1.61%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	1.21%	[2]
State and political subdivisions
Securities available-for-sale:
One year or less	243
Over 1 through 5 years	3,079
Over 5 through 10 years	1,783
Over 10 years	299
Total	5,404
Securities held-to-maturity:
One year or less	1
Over 1 through 5 years	0
Over 5 through 10 years	10
Over 10 years	18
Held-to-maturity (fair value of $20,167 and $19,443)	29
Securities available-for-sale:
One year or less (percent)	1.30%	[2]
Over 1 through 5 years (percent)	2.15%	[2]
Over 5 through 10 years (percent)	3.51%	[2]
Over 10 years (percent)	2.76%	[2]
Total (percent)	2.59%	[2]
Securities held-to-maturity:
One year or less (percent)	3.80%	[2]
Over 1 through 5 years (percent)	0.00%	[2]
Over 5 through 10 years (percent)	6.92%	[2]
Over 10 years (percent)	4.34%	[2]
Total (percent)	5.16%	[2]
Other bonds, notes and debentures
Securities available-for-sale:
One year or less	7,227
Over 1 through 5 years	12,934
Over 5 through 10 years	2,183
Over 10 years	10
Total	22,354
Securities held-to-maturity:
One year or less	3
Over 1 through 5 years	739
Over 5 through 10 years	221
Over 10 years	0
Held-to-maturity (fair value of $20,167 and $19,443)	963
Securities available-for-sale:
One year or less (percent)	0.81%	[2]
Over 1 through 5 years (percent)	1.09%	[2]
Over 5 through 10 years (percent)	2.38%	[2]
Over 10 years (percent)	3.16%	[2]
Total (percent)	1.13%	[2]
Securities held-to-maturity:
One year or less (percent)	0.03%	[2]
Over 1 through 5 years (percent)	0.62%	[2]
Over 5 through 10 years (percent)	0.94%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	0.69%	[2]
Mortgage/ asset-backed and equity securities
Securities available-for-sale:
Total	46,339
Securities held-to-maturity:
Held-to-maturity (fair value of $20,167 and $19,443)	14,635
Securities available-for-sale:
Total (percent)	2.17%	[2]
Securities held-to-maturity:
Total (percent)	2.69%	[2]
Mortgage/ asset-backed and equity securities | Mortgage-backed securities
Securities available-for-sale:
Without single maturity date	40,432
Securities held-to-maturity:
Mortgage-backed securities	14,635
Securities available-for-sale:
Without single maturity date (percent)	2.35%	[2]
Securities held-to-maturity:
Without single maturity date (percent)	2.69%	[2]
Mortgage/ asset-backed and equity securities | Asset-backed securities
Securities available-for-sale:
Without single maturity date	5,021
Securities available-for-sale:
Without single maturity date (percent)	1.09%	[2]
Mortgage/ asset-backed and equity securities | Equity securities
Securities available-for-sale:
Without single maturity date	$ 886	[1]
Securities available-for-sale:
Without single maturity date (percent)	0.00%	[1],[2]

[1] Includes money market funds.

[2] Yields are based upon the amortized cost of securities.