Securities - Distribution of maturities of debt securities with approximate yield of portfolio (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	$ 1,350
Available-for-sale yield within one year	1.06%
Available-for-sale amount after one but within five years	26,789
Available-for-sale yield after one but within five years	0.89%
Available-for-sale amount after five but within ten years	6,386
Available-for-sale yield after five but within ten years	2.88%
Available-for-sale amount after ten years	20,245
Available-for-sale yield after ten years	2.95%
Total fair value within one year	1,353
Total fair value after one but within five years	26,796
Total fair value after five but within ten years	6,648
Total fair value after ten years	19,947
Held-to-maturity amount within one year	6
Held-to-maturity yield within one year	5.85%
Held-to-maturity amount after one but within five years	12
Held-to-maturity yield after one but within five years	4.89%
Held-to-maturity amount after five but within ten years	75
Held-to-maturity yield after five but within ten years	0.98%
Held-to-maturity amount after ten years	1,265
Held-to-maturity yield after ten years	5.59%
Total fair value within one year	6
Total fair value after one but within five years	14
Total fair value after five but within ten years	76
Total fair value after ten years	1,403
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	774
Available-for-sale yield within one year	0.33%
Available-for-sale amount after one but within five years	21,777
Available-for-sale yield after one but within five years	0.62%
Available-for-sale amount after five but within ten years	3,238
Available-for-sale yield after five but within ten years	2.46%
Available-for-sale amount after ten years	1,927
Available-for-sale yield after ten years	4.22%
US Government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	50
Available-for-sale yield within one year	0.38%
Available-for-sale amount after one but within five years	822
Available-for-sale yield after one but within five years	2.28%
Available-for-sale amount after five but within ten years	2,741
Available-for-sale yield after five but within ten years	3.34%
Available-for-sale amount after ten years	702
Available-for-sale yield after ten years	4.15%
Held-to-maturity amount within one year	1
Held-to-maturity yield within one year	7.96%
Held-to-maturity amount after one but within five years	0
Held-to-maturity yield after one but within five years	0.00%
Held-to-maturity amount after five but within ten years	2
Held-to-maturity yield after five but within ten years	8.05%
Held-to-maturity amount after ten years	842
Held-to-maturity yield after ten years	6.15%
U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	0
Available-for-sale yield within one year	0.00%
Available-for-sale amount after one but within five years	14
Available-for-sale yield after one but within five years	4.22%
Available-for-sale amount after five but within ten years	81
Available-for-sale yield after five but within ten years	2.29%
Available-for-sale amount after ten years	16,793
Available-for-sale yield after ten years	2.75%
Held-to-maturity amount within one year	0
Held-to-maturity yield within one year	0.00%
Held-to-maturity amount after one but within five years	1
Held-to-maturity yield after one but within five years	7.64%
Held-to-maturity amount after five but within ten years	2
Held-to-maturity yield after five but within ten years	7.70%
Held-to-maturity amount after ten years	263
Held-to-maturity yield after ten years	6.51%
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	0
Available-for-sale yield within one year	0.00%
Available-for-sale amount after one but within five years	94
Available-for-sale yield after one but within five years	3.98%
Available-for-sale amount after five but within ten years	316
Available-for-sale yield after five but within ten years	3.40%
Available-for-sale amount after ten years	345
Available-for-sale yield after ten years	3.42%
Held-to-maturity amount within one year	5
Held-to-maturity yield within one year	5.40%
Held-to-maturity amount after one but within five years	11
Held-to-maturity yield after one but within five years	4.46%
Held-to-maturity amount after five but within ten years	6
Held-to-maturity yield after five but within ten years	3.92%
Held-to-maturity amount after ten years	7
Held-to-maturity yield after ten years	5.05%
Asset backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	0
Available-for-sale yield within one year	0.00%
Available-for-sale amount after one but within five years	1
Available-for-sale yield after one but within five years	1.82%
Available-for-sale amount after five but within ten years	10
Available-for-sale yield after five but within ten years	0.38%
Available-for-sale amount after ten years	478
Available-for-sale yield after ten years	2.62%
Held-to-maturity amount within one year	0
Held-to-maturity yield within one year	0.00%
Held-to-maturity amount after one but within five years	0
Held-to-maturity yield after one but within five years	0.00%
Held-to-maturity amount after five but within ten years	0
Held-to-maturity yield after five but within ten years	0.00%
Held-to-maturity amount after ten years	18
Held-to-maturity yield after ten years	6.19%
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	526
Available-for-sale yield within one year	2.20%
Available-for-sale amount after one but within five years	4,081
Available-for-sale yield after one but within five years	1.94%
Available-for-sale amount after five but within ten years
Available-for-sale yield after five but within ten years	0.00%
Available-for-sale amount after ten years	0
Available-for-sale yield after ten years	0.00%
Asset backed securities and other debt securities of VIE [Member]
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity amount within one year	0
Held-to-maturity yield within one year	0.00%
Held-to-maturity amount after one but within five years	0
Held-to-maturity yield after one but within five years	0.00%
Held-to-maturity amount after five but within ten years	65
Held-to-maturity yield after five but within ten years	0.28%
Held-to-maturity amount after ten years	$ 135
Held-to-maturity yield after ten years	0.28%