Investment Securities - Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013 Y	Dec. 31, 2012
Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost	$ 39,590
Available-for-sale securities, total, fair value	40,570
Available-for-sale securities, total, weighted average maturity in years	4.4
Available-for-sale securities, total, weighted average yield	2.80%
Held-to-maturity securities, other investments, amortized cost	34,716	34,389
Held-to-maturity securities, Fair Value	35,183	34,952
Held-to-maturity securities, total, fair value	35,183	34,952
Held-to-maturity securities, total, weighted average maturity in years	3.6
Held-to-maturity securities, total, weighted average yield	1.91%
Total investment securities amortized cost	74,306	73,429
Total investment securities, percentage	100.00%	100.00%
U.S. Treasury and Agencies [Member]
Investment Securities [Line Items]
Available-for-sale, securities maturing within one year, amortized cost	1,201
Available-for-sale, securities maturing after one through five year, amortized cost	139
Available-for-sale, securities maturing after five through ten year, amortized cost	152
Available-for-sale, securities maturing after ten years, amortized cost	1
Available-for-sale securities, total, amortized cost	1,493
Available-for-sale, securities maturing within one year, fair value	1,202
Available-for-sale, securities maturing after one through five year, fair value	141
Available-for-sale, securities maturing after five through ten year, fair value	161
Available-for-sale, securities maturing after ten years, fair value	2
Available-for-sale securities, total, fair value	1,506
Available-for-sale securities, maturing in one year or less, weighted average maturity in years	0.7
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years	1.6
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years	7.3
Available-for-sale securities, maturing after ten years, weighted average maturity in years	14.4
Available-for-sale securities, total, weighted average maturity in years	1.4
Available-for-sale securities, maturing in one year or less, weighted average yield	1.47%
Available for sale securities, maturing after one year through five years weighted average yield	2.34%
Available-for-sale securities, maturing after five years through ten years, weighted average yield	3.13%
Available-for-sale securities, maturing after ten years, weighted average yield	4.15%
Available-for-sale securities, total, weighted average yield	1.72%
Held-to-maturity securities, maturities within one year, amortized cost	1,411
Held-to-maturity securities, maturities after one year through five years, amortized cost	1,034
Held-to-maturity securities, maturities after five years through ten years, amortized cost	968
Held-to-maturity securities, maturities after ten years, amortized cost	60
Held-to-maturity securities, total, amortized cost	3,473
Held-to-maturity securities, maturities within one year, fair value	1,420
Held to maturity securities, maturities after one year through five years, fair value	1,043
Held-to-maturity securities, maturities after five year through ten years, fair value	971
Held-to-maturity securities, maturities after ten years, fair value	60
Held-to-maturity securities, Fair Value	3,494
Held-to-maturity securities, maturing in one year or less, weighted average maturity years	0.7
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years	1.2
Held to maturity securities, maturing after five year through ten years, weighted average maturity in years	9.3
Held-to-maturity securities, maturing after ten years, weighted average maturity in years	11.9
Held-to-maturity securities, total, weighted average maturity in years	3.5
Held-to-maturity securities, maturing in one year or less, weighted average yield	0.97%
Held-to-maturity securities, maturing after one year through five years, weighted average yield	1.03%
Held-to-maturity securities, maturing after five year through ten years, weighted average yield	1.86%
Held-to-maturity securities, maturing after ten years, weighted average yield	1.81%
Held-to-maturity securities, total, weighted average yield	1.25%
Total investment securities amortized cost	4,966	4,365
Total investment securities, percentage	6.70%	5.90%
Mortgage-Backed Securities [Member]
Investment Securities [Line Items]
Available-for-sale, securities maturing within one year, amortized cost	1,767
Available-for-sale, securities maturing after one through five year, amortized cost	21,662
Available-for-sale, securities maturing after five through ten year, amortized cost	6,139
Available-for-sale, securities maturing after ten years, amortized cost	403
Available-for-sale securities, total, amortized cost	29,971
Available-for-sale, securities maturing within one year, fair value	1,776
Available-for-sale, securities maturing after one through five year, fair value	22,212
Available-for-sale, securities maturing after five through ten year, fair value	6,200
Available-for-sale, securities maturing after ten years, fair value	409
Available-for-sale securities, total, fair value	30,597
Available-for-sale securities, maturing in one year or less, weighted average maturity in years	0.6
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years	3.5
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years	6.1
Available-for-sale securities, maturing after ten years, weighted average maturity in years	12.2
Available-for-sale securities, total, weighted average maturity in years	3.9
Available-for-sale securities, maturing in one year or less, weighted average yield	1.70%
Available for sale securities, maturing after one year through five years weighted average yield	2.27%
Available-for-sale securities, maturing after five years through ten years, weighted average yield	1.85%
Available-for-sale securities, maturing after ten years, weighted average yield	1.62%
Available-for-sale securities, total, weighted average yield	2.14%
Held-to-maturity securities, maturities within one year, amortized cost	194
Held-to-maturity securities, maturities after one year through five years, amortized cost	27,931
Held-to-maturity securities, maturities after five years through ten years, amortized cost	2,834
Held-to-maturity securities, maturities after ten years, amortized cost	122
Held-to-maturity securities, total, amortized cost	31,081
Held-to-maturity securities, maturities within one year, fair value	194
Held to maturity securities, maturities after one year through five years, fair value	28,355
Held-to-maturity securities, maturities after five year through ten years, fair value	2,856
Held-to-maturity securities, maturities after ten years, fair value	125
Held-to-maturity securities, Fair Value	31,530
Held-to-maturity securities, maturing in one year or less, weighted average maturity years	0.6
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years	3.3
Held to maturity securities, maturing after five year through ten years, weighted average maturity in years	5.9
Held-to-maturity securities, maturing after ten years, weighted average maturity in years	11.0
Held-to-maturity securities, total, weighted average maturity in years	3.6
Held-to-maturity securities, maturing in one year or less, weighted average yield	1.55%
Held-to-maturity securities, maturing after one year through five years, weighted average yield	2.04%
Held-to-maturity securities, maturing after five year through ten years, weighted average yield	1.41%
Held-to-maturity securities, maturing after ten years, weighted average yield	1.29%
Held-to-maturity securities, total, weighted average yield	1.98%
Total investment securities amortized cost	61,052	61,019
Total investment securities, percentage	82.10%	83.10%
Asset-Backed Securities [Member]
Investment Securities [Line Items]
Available-for-sale, securities maturing within one year, amortized cost	0
Available-for-sale, securities maturing after one through five year, amortized cost	55
Available-for-sale, securities maturing after five through ten year, amortized cost	565
Available-for-sale, securities maturing after ten years, amortized cost	0
Available-for-sale securities, total, amortized cost	620
Available-for-sale, securities maturing within one year, fair value	0
Available-for-sale, securities maturing after one through five year, fair value	64
Available-for-sale, securities maturing after five through ten year, fair value	575
Available-for-sale, securities maturing after ten years, fair value	0
Available-for-sale securities, total, fair value	639
Available-for-sale securities, maturing in one year or less, weighted average maturity in years	0.1
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years	3.2
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years	7.2
Available-for-sale securities, maturing after ten years, weighted average maturity in years	18.3
Available-for-sale securities, total, weighted average maturity in years	6.9
Available-for-sale securities, maturing in one year or less, weighted average yield	7.66%
Available for sale securities, maturing after one year through five years weighted average yield	2.60%
Available-for-sale securities, maturing after five years through ten years, weighted average yield	2.26%
Available-for-sale securities, maturing after ten years, weighted average yield	5.39%
Available-for-sale securities, total, weighted average yield	2.29%
Held-to-maturity securities, maturities after one year through five years, amortized cost	9
Held-to-maturity securities, maturities after five years through ten years, amortized cost	8
Held-to-maturity securities, maturities after ten years, amortized cost	5
Held-to-maturity securities, total, amortized cost	22
Held-to-maturity securities, maturities within one year, fair value	0
Held to maturity securities, maturities after one year through five years, fair value	9
Held-to-maturity securities, maturities after five year through ten years, fair value	11
Held-to-maturity securities, maturities after ten years, fair value	13
Held-to-maturity securities, Fair Value	33
Held-to-maturity securities, maturing in one year or less, weighted average maturity years	0.3
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years	3.3
Held to maturity securities, maturing after five year through ten years, weighted average maturity in years	6.8
Held-to-maturity securities, maturing after ten years, weighted average maturity in years	22.0
Held-to-maturity securities, total, weighted average maturity in years	8.9
Held-to-maturity securities, maturing in one year or less, weighted average yield	0.43%
Held-to-maturity securities, maturing after one year through five years, weighted average yield	0.74%
Held-to-maturity securities, maturing after five year through ten years, weighted average yield	0.84%
Held-to-maturity securities, maturing after ten years, weighted average yield	0.75%
Held-to-maturity securities, total, weighted average yield	0.78%
Total investment securities amortized cost	642	637
Total investment securities, percentage	0.90%	0.90%
Obligations of State and Political Subdivisions [Member]
Investment Securities [Line Items]
Available-for-sale, securities maturing within one year, amortized cost	38
Available-for-sale, securities maturing after one through five year, amortized cost	5,225
Available-for-sale, securities maturing after five through ten year, amortized cost	614
Available-for-sale, securities maturing after ten years, amortized cost	50
Available-for-sale securities, total, amortized cost	5,927
Available-for-sale, securities maturing within one year, fair value	38
Available-for-sale, securities maturing after one through five year, fair value	5,552
Available-for-sale, securities maturing after five through ten year, fair value	640
Available-for-sale, securities maturing after ten years, fair value	50
Available-for-sale securities, total, fair value	6,280
Available-for-sale securities, maturing in one year or less, weighted average maturity in years	0.5
Available-for-sale securities, maturing after one year through five years, weighted average maturity in years	3.4
Available-for-sale securities, maturing after five years through ten years, weighted average maturity in years	7.8
Available-for-sale securities, maturing after ten years, weighted average maturity in years	21.2
Available-for-sale securities, total, weighted average maturity in years	3.9
Available-for-sale securities, maturing in one year or less, weighted average yield	7.14%
Available for sale securities, maturing after one year through five years weighted average yield	6.73%
Available-for-sale securities, maturing after five years through ten years, weighted average yield	5.76%
Available-for-sale securities, maturing after ten years, weighted average yield	8.07%
Available-for-sale securities, total, weighted average yield	6.65%
Held-to-maturity securities, maturities within one year, amortized cost	1
Held-to-maturity securities, maturities after one year through five years, amortized cost	4
Held-to-maturity securities, maturities after five years through ten years, amortized cost	2
Held-to-maturity securities, maturities after ten years, amortized cost	12
Held-to-maturity securities, total, amortized cost	19
Held-to-maturity securities, maturities within one year, fair value	1
Held to maturity securities, maturities after one year through five years, fair value	5
Held-to-maturity securities, maturities after five year through ten years, fair value	2
Held-to-maturity securities, maturities after ten years, fair value	12
Held-to-maturity securities, Fair Value	20
Held-to-maturity securities, maturing in one year or less, weighted average maturity years	0.6
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years	2.9
Held to maturity securities, maturing after five year through ten years, weighted average maturity in years	8.0
Held-to-maturity securities, maturing after ten years, weighted average maturity in years	14.5
Held-to-maturity securities, total, weighted average maturity in years	10.8
Held-to-maturity securities, maturing in one year or less, weighted average yield	6.88%
Held-to-maturity securities, maturing after one year through five years, weighted average yield	7.47%
Held-to-maturity securities, maturing after five year through ten years, weighted average yield	7.72%
Held-to-maturity securities, maturing after ten years, weighted average yield	5.36%
Held-to-maturity securities, total, weighted average yield	6.12%
Total investment securities amortized cost	5,946	6,079
Total investment securities, percentage	8.00%	8.30%
Other debt securities and obligations of foreign government [Member]
Investment Securities [Line Items]
Available-for-sale, securities maturing within one year, amortized cost	6
Available-for-sale, securities maturing after one through five year, amortized cost	0
Available-for-sale, securities maturing after five through ten year, amortized cost	0
Available-for-sale, securities maturing after ten years, amortized cost	814
Available-for-sale securities, total, amortized cost	820
Available-for-sale, securities maturing within one year, fair value	6
Available-for-sale, securities maturing after one through five year, fair value	0
Available-for-sale, securities maturing after five through ten year, fair value	0
Available-for-sale, securities maturing after ten years, fair value	740
Available-for-sale securities, total, fair value	746
Available-for-sale securities, maturing in one year or less, weighted average maturity in years	0.9
Available-for-sale securities, maturing after ten years, weighted average maturity in years	24.2
Available-for-sale securities, total, weighted average maturity in years	24.0
Available-for-sale securities, maturing in one year or less, weighted average yield	1.15%
Available-for-sale securities, maturing after ten years, weighted average yield	3.12%
Available-for-sale securities, total, weighted average yield	3.11%
Held-to-maturity securities, maturities within one year, amortized cost	1
Held-to-maturity securities, maturities after one year through five years, amortized cost	94
Held-to-maturity securities, maturities after five years through ten years, amortized cost	26
Held-to-maturity securities, maturities after ten years, amortized cost	0
Held-to-maturity securities, total, amortized cost	121
Held-to-maturity securities, maturities within one year, fair value	1
Held to maturity securities, maturities after one year through five years, fair value	93
Held-to-maturity securities, maturities after five year through ten years, fair value	12
Held-to-maturity securities, maturities after ten years, fair value	0
Held-to-maturity securities, Fair Value	106
Held-to-maturity securities, maturing in one year or less, weighted average maturity years	0.4
Held-to-maturity securities, maturing after one year through five years, weighted average maturity in years	3.0
Held to maturity securities, maturing after five year through ten years, weighted average maturity in years	7.6
Held-to-maturity securities, total, weighted average maturity in years	3.9
Held-to-maturity securities, maturing in one year or less, weighted average yield	1.00%
Held-to-maturity securities, maturing after one year through five years, weighted average yield	1.19%
Held-to-maturity securities, maturing after five year through ten years, weighted average yield	1.03%
Held-to-maturity securities, total, weighted average yield	1.16%
Total investment securities amortized cost	1,700	1,329
Total investment securities, percentage	2.30%	1.80%
Other Investments Including Perpetual Preferred Securities [Member]
Investment Securities [Line Items]
Available-for-sale securities, total, amortized cost	759
Available-for-sale securities, total, fair value	802
Available-for-sale securities, total, weighted average maturity in years	8.7
Available-for-sale securities, total, weighted average yield	1.29%
Held-to-maturity securities, other investments, amortized cost	0
Held-to-maturity securities, total, fair value	$ 0