Securities - Distribution of maturities of debt securities with approximate yield of portfolio (Detail) $ in Millions	Jun. 30, 2016 USD ($)
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Available-for-sale amount within one year	$ 817
Available-for-sale yield within one year	1.84%
Available-for-sale amount after one but within five years	$ 9,072
Available-for-sale yield after one but within five years	1.86%
Available-for-sale amount after five but within ten years	$ 10,451
Available-for-sale yield after five but within ten years	2.19%
Available-for-sale amount after ten years	$ 17,355
Available-for-sale yield after ten years	2.37%
Total fair value within one year	$ 821
Total fair value after one but within five years	9,319
Total fair value after five but within ten years	10,749
Total fair value after ten years	17,376
Held-to-maturity amount within one year	$ 3
Held-to-maturity yield within one year	3.70%
Held-to-maturity amount after one but within five years	$ 144
Held-to-maturity yield after one but within five years	1.68%
Held-to-maturity after five but within ten years	$ 612
Held-to-maturity yield after five but within ten years	2.74%
Held-to-maturity after ten years	$ 12,456
Held-to-maturity yield after ten years	2.52%
Total fair value within one year	$ 3
Total fair value after one but within five years	146
Total fair value after five but within ten years	643
Total fair value after ten years	12,809
U.S. Treasury [Member]
Schedule of Available-for-sale and Held-to-Maturity 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	$ 5,525
Available-for-sale yield after one but within five years	1.30%
Available-for-sale amount after five but within ten years	$ 9,317
Available-for-sale yield after five but within ten years	2.17%
Available-for-sale amount after ten years	$ 5,145
Available-for-sale yield after ten years	2.59%
US Government sponsored enterprises [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Available-for-sale amount within one year	$ 120
Available-for-sale yield within one year	3.23%
Available-for-sale amount after one but within five years	$ 3,315
Available-for-sale yield after one but within five years	2.83%
Available-for-sale amount after five but within ten years	$ 1,105
Available-for-sale yield after five but within ten years	2.32%
Available-for-sale amount after ten years	$ 4,543
Available-for-sale yield after ten years	2.06%
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	$ 130
Held-to-maturity yield after one but within five years	1.61%
Held-to-maturity after five but within ten years	$ 570
Held-to-maturity yield after five but within ten years	2.70%
Held-to-maturity after ten years	$ 3,634
Held-to-maturity yield after ten years	2.92%
US Government agency issued or guaranteed [Member]
Schedule of Available-for-sale and Held-to-Maturity 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	$ 4
Available-for-sale yield after one but within five years	3.99%
Available-for-sale amount after five but within ten years	$ 29
Available-for-sale yield after five but within ten years	3.81%
Available-for-sale amount after ten years	$ 7,467
Available-for-sale yield after ten years	2.38%
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	$ 9
Held-to-maturity yield after one but within five years	1.55%
Held-to-maturity after five but within ten years	$ 37
Held-to-maturity yield after five but within ten years	3.21%
Held-to-maturity after ten years	$ 8,812
Held-to-maturity yield after ten years	2.35%
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale and Held-to-Maturity 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	$ 13
Available-for-sale yield after one but within five years	4.26%
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%
Held-to-maturity amount within one year	$ 3
Held-to-maturity yield within one year	3.70%
Held-to-maturity amount after one but within five years	$ 5
Held-to-maturity yield after one but within five years	3.71%
Held-to-maturity after five but within ten years	$ 5
Held-to-maturity yield after five but within ten years	3.70%
Held-to-maturity after ten years	$ 4
Held-to-maturity yield after ten years	5.60%
Asset backed securities [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Available-for-sale amount within one year	$ 400
Available-for-sale yield within one year	1.88%
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	$ 200
Available-for-sale yield after ten years	3.17%
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	$ 6
Held-to-maturity yield after ten years	6.60%
Foreign debt securities [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Available-for-sale amount within one year	$ 297
Available-for-sale yield within one year	1.23%
Available-for-sale amount after one but within five years	$ 215
Available-for-sale yield after one but within five years	1.07%
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%