Securities - Distribution of maturities of debt securities with approximate yield of portfolio (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	$ 8,368
Available-for-sale yield within one year	0.52%
Available-for-sale amount after one but within five years	15,275
Available-for-sale yield after one but within five years	1.07%
Available-for-sale amount after five but within ten years	6,055
Available-for-sale yield after five but within ten years	2.84%
Available-for-sale amount after ten years	22,570
Available-for-sale yield after ten years	2.77%
Total fair value within one year	8,376
Total fair value after one but within five years	15,270
Total fair value after five but within ten years	6,451
Total fair value after ten years	22,596
Held-to-maturity amount within one year	7
Held-to-maturity yield within one year	5.85%
Held-to-maturity amount after one but within five years	15
Held-to-maturity yield after one but within five years	5.61%
Held-to-maturity amount after five but within ten years	79
Held-to-maturity yield after five but within ten years	0.99%
Held-to-maturity amount after ten years	1,437
Held-to-maturity yield after ten years	5.63%
Total fair value within one year	7
Total fair value after one but within five years	16
Total fair value after five but within ten years	81
Total fair value after ten years	1,610
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	7,597
Available-for-sale yield within one year	0.30%
Available-for-sale amount after one but within five years	10,424
Available-for-sale yield after one but within five years	0.62%
Available-for-sale amount after five but within ten years	2,821
Available-for-sale yield after five but within ten years	2.42%
Available-for-sale amount after ten years	1,965
Available-for-sale yield after ten years	3.92%
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	0.39%
Available-for-sale amount after one but within five years	515
Available-for-sale yield after one but within five years	2.49%
Available-for-sale amount after five but within ten years	2,798
Available-for-sale yield after five but within ten years	3.19%
Available-for-sale amount after ten years	767
Available-for-sale yield after ten years	3.91%
Held-to-maturity amount within one year	2
Held-to-maturity yield within one year	7.98%
Held-to-maturity amount after one but within five years	2
Held-to-maturity yield after one but within five years	7.45%
Held-to-maturity amount after five but within ten years	1
Held-to-maturity yield after five but within ten years	7.91%
Held-to-maturity amount after ten years	951
Held-to-maturity yield after ten years	6.16%
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	6
Available-for-sale yield after one but within five years	5.09%
Available-for-sale amount after five but within ten years	102
Available-for-sale yield after five but within ten years	2.43%
Available-for-sale amount after ten years	18,800
Available-for-sale yield after ten years	2.59%
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	7.61%
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	298
Held-to-maturity yield after ten years	6.51%
Obligations of U.S. states and political subdivisions [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	74
Available-for-sale yield after one but within five years	3.90%
Available-for-sale amount after five but within ten years	323
Available-for-sale yield after five but within ten years	3.72%
Available-for-sale amount after ten years	477
Available-for-sale yield after ten years	3.49%
Held-to-maturity amount within one year	5
Held-to-maturity yield within one year	5.10%
Held-to-maturity amount after one but within five years	12
Held-to-maturity yield after one but within five years	5.06%
Held-to-maturity amount after five but within ten years	7
Held-to-maturity yield after five but within ten years	4.03%
Held-to-maturity amount after ten years	9
Held-to-maturity yield after ten years	5.02%
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	1.99%
Available-for-sale amount after five but within ten years	11
Available-for-sale yield after five but within ten years	0.40%
Available-for-sale amount after ten years	538
Available-for-sale yield after ten years	2.74%
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	30
Held-to-maturity yield after ten years	6.37%
Corporate and other domestic [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	0
Available-for-sale yield after one but within five years	0.00%
Available-for-sale amount after five but within ten years	0
Available-for-sale yield after five but within ten years	0.00%
Available-for-sale amount after ten years	23
Available-for-sale yield after ten years	3.90%
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	721
Available-for-sale yield within one year	2.85%
Available-for-sale amount after one but within five years	4,255
Available-for-sale yield after one but within five years	1.95%
Available-for-sale amount after five but within ten years	0
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	69
Held-to-maturity yield after five but within ten years	0.30%
Held-to-maturity amount after ten years	$ 149
Held-to-maturity yield after ten years	0.36%