Securities - Distribution of maturities of debt securities with approximate yield of portfolio (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	$ 1,779
Available-for-sale yield within one year	1.20%
Available-for-sale amount after one but within five years	19,196
Available-for-sale yield after one but within five years	1.24%
Available-for-sale amount after five but within ten years	5,295
Available-for-sale yield after five but within ten years	3.09%
Available-for-sale amount after ten years	17,872
Available-for-sale yield after ten years	2.61%
Total fair value within one year	1,781
Total fair value after one but within five years	19,299
Total fair value after five but within ten years	5,587
Total fair value after ten years	17,945
Held-to-maturity amount within one year	5
Held-to-maturity yield within one year	5.28%
Held-to-maturity amount after one but within five years	9
Held-to-maturity yield after one but within five years	4.79%
Held-to-maturity after five but within ten years	74
Held-to-maturity yield after five but within ten years	1.05%
Held-to-maturity after ten years	1,117
Held-to-maturity yield after ten years	5.72%
Total fair value within one year	5
Total fair value after one but within five years	11
Total fair value after five but within ten years	78
Total fair value after ten years	1,278
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	1,225
Available-for-sale yield within one year	0.34%
Available-for-sale amount after one but within five years	14,017
Available-for-sale yield after one but within five years	0.91%
Available-for-sale amount after five but within ten years	2,429
Available-for-sale yield after five but within ten years	2.90%
Available-for-sale amount after ten years	1,835
Available-for-sale yield after ten years	3.80%
US Government sponsored enterprises [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	1,108
Available-for-sale yield after one but within five years	2.62%
Available-for-sale amount after five but within ten years	2,450
Available-for-sale yield after five but within ten years	3.27%
Available-for-sale amount after ten years	777
Available-for-sale yield after ten years	3.74%
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 after five but within ten years	2
Held-to-maturity yield after five but within ten years	7.77%
Held-to-maturity after ten years	761
Held-to-maturity yield after ten years	6.14%
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	12
Available-for-sale yield after one but within five years	4.23%
Available-for-sale amount after five but within ten years	107
Available-for-sale yield after five but within ten years	2.65%
Available-for-sale amount after ten years	14,656
Available-for-sale yield after ten years	2.36%
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	7.62%
Held-to-maturity after five but within ten years	2
Held-to-maturity yield after five but within ten years	7.75%
Held-to-maturity after ten years	238
Held-to-maturity yield after ten years	6.49%
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	110
Available-for-sale yield after one but within five years	3.66%
Available-for-sale amount after five but within ten years	302
Available-for-sale yield after five but within ten years	3.32%
Available-for-sale amount after ten years	316
Available-for-sale yield after ten years	3.52%
Held-to-maturity amount within one year	5
Held-to-maturity yield within one year	5.28%
Held-to-maturity amount after one but within five years	8
Held-to-maturity yield after one but within five years	4.40%
Held-to-maturity after five but within ten years	6
Held-to-maturity yield after five but within ten years	3.94%
Held-to-maturity after ten years	7
Held-to-maturity yield after ten years	5.04%
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	0
Available-for-sale yield after one but within five years	0.00%
Available-for-sale amount after five but within ten years	7
Available-for-sale yield after five but within ten years	0.39%
Available-for-sale amount after ten years	288
Available-for-sale yield after ten years	3.56%
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 after five but within ten years	0
Held-to-maturity yield after five but within ten years	0.00%
Held-to-maturity after ten years	18
Held-to-maturity yield after ten years	6.21%
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale amount within one year	554
Available-for-sale yield within one year	3.10%
Available-for-sale amount after one but within five years	3,949
Available-for-sale yield after one but within five years	1.94%
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 issued by consolidated 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 after five but within ten years	64
Held-to-maturity yield after five but within ten years	0.33%
Held-to-maturity after ten years	$ 93
Held-to-maturity yield after ten years	0.33%