Maturity Distribution by Carrying Amount and Yield (on Tax Equivalent Basis) of Investment Securities Portfolio (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Securities available-for-sale, amount:
One year or less	$ 3,221
Over 1 through 5 years	25,915
Over 5 through 10 years	6,016
Over 10 years	3,237
Total	83,374
Securities held-to-maturity, amount:
One year or less	4
Over 1 through 5 years	554
Over 5 through 10 years	382
Over 10 years	62
Total	4,849
Mortgage-Backed Securities
Securities available-for-sale, amount:
Without single maturity date	42,074
Securities held-to-maturity, amount:
Without single maturity date	3,847
Asset-Backed Securities
Securities available-for-sale, amount:
Without single maturity date	1,920
Equity Securities
Securities available-for-sale, amount:
Without single maturity date	991	[1]
U.S. Treasury
Securities available-for-sale, amount:
One year or less	229
Over 1 through 5 years	9,233
Over 5 through 10 years	2,263
Over 10 years	2,526
Total	14,251
Securities held-to-maturity, amount:
Over 1 through 5 years	554
Over 5 through 10 years	351
Total	905
Securities available-for-sale, yield:
One year or less	0.66%	[2]
Over 1 through 5 years	0.98%	[2]
Over 5 through 10 years	2.83%	[2]
Over 10 years	3.13%	[2]
Total	1.65%	[2]
Securities held-to-maturity, yield:
Over 1 through 5 years	1.82%	[2]
Over 5 through 10 years	2.65%	[2]
Total	2.14%	[2]
U.S. Government Agencies
Securities available-for-sale, amount:
Over 1 through 5 years	1,009
Over 5 through 10 years	99
Total	1,108
Securities available-for-sale, yield:
Over 1 through 5 years	1.61%	[2]
Over 5 through 10 years	0.02%	[2]
Total	1.65%	[2]
State And Political Subdivisions
Securities available-for-sale, amount:
One year or less	89
Over 1 through 5 years	1,784
Over 5 through 10 years	1,608
Over 10 years	492
Total	3,973
Securities held-to-maturity, amount:
One year or less	1
Over 5 through 10 years	31
Over 10 years	62
Total	94
Securities available-for-sale, yield:
One year or less	1.17%	[2]
Over 1 through 5 years	1.68%	[2]
Over 5 through 10 years	3.45%	[2]
Over 10 years	5.07%	[2]
Total	2.80%	[2]
Securities held-to-maturity, yield:
One year or less	6.87%	[2]
Over 5 through 10 years	6.65%	[2]
Over 10 years	6.57%	[2]
Total	6.60%	[2]
Other bonds, Notes and Debentures
Securities available-for-sale, amount:
One year or less	2,903
Over 1 through 5 years	13,889
Over 5 through 10 years	2,046
Over 10 years	219
Total	19,057
Securities held-to-maturity, amount:
One year or less	3
Total	3
Securities available-for-sale, yield:
One year or less	1.16%	[2]
Over 1 through 5 years	1.47%	[2]
Over 5 through 10 years	2.98%	[2]
Over 10 years	5.09%	[2]
Total	1.62%	[2]
Securities held-to-maturity, yield:
One year or less	0.11%	[2]
Total	0.11%	[2]
Mortgage/Asset-Backed and Equity Securities
Securities available-for-sale, amount:
Total	44,985
Securities held-to-maturity, amount:
Total	3,847
Securities available-for-sale, yield:
Total	3.74%	[2]
Securities held-to-maturity, yield:
Total	2.49%	[2]
Mortgage/Asset-Backed and Equity Securities | Mortgage-Backed Securities
Securities available-for-sale, amount:
Without single maturity date	42,074
Securities held-to-maturity, amount:
Without single maturity date	3,847
Securities available-for-sale, yield:
Without single maturity date	3.90%	[2]
Securities held-to-maturity, yield:
Without single maturity date	2.49%	[2]
Mortgage/Asset-Backed and Equity Securities | Asset-Backed Securities
Securities available-for-sale, amount:
Without single maturity date	1,920
Securities available-for-sale, yield:
Without single maturity date	2.02%	[2]
Mortgage/Asset-Backed and Equity Securities | Equity Securities
Securities available-for-sale, amount:
Without single maturity date	$ 991	[1]

[1] Includes money market funds.

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