Securities-Maturity Distribution by Carrying Amount and Yield (on Tax Equivalent Basis) of Investment Securities Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Securities available-for-sale:
One year or less	$ 7,429
Over 1 through 5 years	21,293
Over 5 through 10 years	6,404
Over 10 years	4,256
Total	80,216
Securities held-to-maturity:
One year or less	4
Over 1 through 5 years	3,454
Over 5 through 10 years	1,023
Over 10 years	23
Held-to-maturity (fair value of $19,092 and $19,443)	19,226
Mortgage-backed securities
Securities available-for-sale:
Without single maturity date	35,155
Securities held-to-maturity:
Mortgage-backed securities	14,722
Asset-backed securities
Securities available-for-sale:
Without single maturity date	4,813
Equity securities
Securities available-for-sale:
Without single maturity date	866	[1]
U.S. Treasury
Securities available-for-sale:
One year or less	387
Over 1 through 5 years	7,991
Over 5 through 10 years	1,313
Over 10 years	3,881
Total	13,572
Securities held-to-maturity:
One year or less	0
Over 1 through 5 years	2,429
Over 5 through 10 years	896
Over 10 years	0
Held-to-maturity (fair value of $19,092 and $19,443)	3,325
Securities available-for-sale:
One year or less (percent)	0.47%	[2]
Over 1 through 5 years (percent)	0.68%	[2]
Over 5 through 10 years (percent)	2.85%	[2]
Over 10 years (percent)	3.12%	[2]
Total (percent)	1.58%	[2]
Securities held-to-maturity:
One year or less (percent)	0.00%	[2]
Over 1 through 5 years (percent)	1.22%	[2]
Over 5 through 10 years (percent)	2.24%	[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	171
Over 1 through 5 years	180
Over 5 through 10 years	98
Over 10 years	0
Total	449
Securities held-to-maturity:
One year or less	0
Over 1 through 5 years	308
Over 5 through 10 years	111
Over 10 years	0
Held-to-maturity (fair value of $19,092 and $19,443)	419
Securities available-for-sale:
One year or less (percent)	1.64%	[2]
Over 1 through 5 years (percent)	2.06%	[2]
Over 5 through 10 years (percent)	1.49%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	1.78%	[2]
Securities held-to-maturity:
One year or less (percent)	0.00%	[2]
Over 1 through 5 years (percent)	1.18%	[2]
Over 5 through 10 years (percent)	1.61%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	1.29%	[2]
State and political subdivisions
Securities available-for-sale:
One year or less	514
Over 1 through 5 years	3,208
Over 5 through 10 years	2,561
Over 10 years	369
Total	6,652
Securities held-to-maturity:
One year or less	1
Over 1 through 5 years	0
Over 5 through 10 years	16
Over 10 years	23
Held-to-maturity (fair value of $19,092 and $19,443)	40
Securities available-for-sale:
One year or less (percent)	1.54%	[2]
Over 1 through 5 years (percent)	1.98%	[2]
Over 5 through 10 years (percent)	3.41%	[2]
Over 10 years (percent)	3.41%	[2]
Total (percent)	2.57%	[2]
Securities held-to-maturity:
One year or less (percent)	4.00%	[2]
Over 1 through 5 years (percent)	0.00%	[2]
Over 5 through 10 years (percent)	6.82%	[2]
Over 10 years (percent)	4.86%	[2]
Total (percent)	5.61%	[2]
Other bonds, notes and debentures
Securities available-for-sale:
One year or less	6,357
Over 1 through 5 years	9,914
Over 5 through 10 years	2,432
Over 10 years	6
Total	18,709
Securities held-to-maturity:
One year or less	3
Over 1 through 5 years	717
Over 5 through 10 years	0
Over 10 years	0
Held-to-maturity (fair value of $19,092 and $19,443)	720
Securities available-for-sale:
One year or less (percent)	1.00%	[2]
Over 1 through 5 years (percent)	1.19%	[2]
Over 5 through 10 years (percent)	2.42%	[2]
Over 10 years (percent)	2.82%	[2]
Total (percent)	1.29%	[2]
Securities held-to-maturity:
One year or less (percent)	0.14%	[2]
Over 1 through 5 years (percent)	0.54%	[2]
Over 5 through 10 years (percent)	0.00%	[2]
Over 10 years (percent)	0.00%	[2]
Total (percent)	0.54%	[2]
Mortgage/ asset-backed and equity securities
Securities available-for-sale:
Total	40,834
Securities held-to-maturity:
Held-to-maturity (fair value of $19,092 and $19,443)	14,722
Securities available-for-sale:
Total (percent)	2.22%	[2]
Securities held-to-maturity:
Total (percent)	2.70%	[2]
Mortgage/ asset-backed and equity securities | Mortgage-backed securities
Securities available-for-sale:
Without single maturity date	35,155
Securities held-to-maturity:
Mortgage-backed securities	14,722
Securities available-for-sale:
Without single maturity date (percent)	2.43%	[2]
Securities held-to-maturity:
Without single maturity date (percent)	2.70%	[2]
Mortgage/ asset-backed and equity securities | Asset-backed securities
Securities available-for-sale:
Without single maturity date	4,813
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	$ 866	[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.