Securities (Details 4) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount within one year	$ 1,795
Available-for-sale yield within one year	2.08%
Available-for-sale amount after one but within five years	28,054
Available-for-sale yield after one but within five years	0.84%
Available-for-sale amount after five but within ten years	4,668
Available-for-sale yield after five but within ten years	3.45%
Available-for-sale amount after ten years	24,116
Available-for-sale yield after ten years	3.37%
Total fair value within one year	1,796
Total fair value after one but within five years	28,067
Total fair value after five but within ten years	5,262
Total fair value after ten years	25,185
Held-to-maturity amount within one year	4
Held-to-maturity yield within one year	5.73%
Held-to-maturity amount after one but within five years	27
Held-to-maturity yield after one but within five years	4.80%
Held-to-maturity amount after five but within ten years	15
Held-to-maturity yield after five but within ten years	4.81%
Held-to-maturity amount after ten years	1,798
Held-to-maturity yield after ten years	5.78%
Total fair value within one year	4
Total fair value after one but within five years	29
Total fair value after five but within ten years	15
Total fair value after ten years	2,032
U.S. Treasury [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount within one year	505
Available-for-sale yield within one year	0.20%
Available-for-sale amount after one but within five years	22,266
Available-for-sale yield after one but within five years	0.56%
Available-for-sale amount after five but within ten years	1,928
Available-for-sale yield after five but within ten years	3.17%
Available-for-sale amount after ten years	3,187
Available-for-sale yield after ten years	3.25%
U.S. Government sponsored enterprises [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount after one but within five years	155
Available-for-sale yield after one but within five years	2.32%
Available-for-sale amount after five but within ten years	2,353
Available-for-sale yield after five but within ten years	3.65%
Available-for-sale amount after ten years	656
Available-for-sale yield after ten years	3.58%
Held-to-maturity amount after one but within five years	10
Held-to-maturity yield after one but within five years	6.12%
Held-to-maturity amount after five but within ten years	1
Held-to-maturity yield after five but within ten years	9.36%
Held-to-maturity amount after ten years	1,279
Held-to-maturity yield after ten years	5.83%
U.S. Government agency issued or guaranteed [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount after one but within five years	6
Available-for-sale yield after one but within five years	4.61%
Available-for-sale amount after five but within ten years	74
Available-for-sale yield after five but within ten years	1.93%
Available-for-sale amount after ten years	19,194
Available-for-sale yield after ten years	3.38%
Held-to-maturity amount after one but within five years	1
Held-to-maturity yield after one but within five years	8.85%
Held-to-maturity amount after five but within ten years	4
Held-to-maturity yield after five but within ten years	9.18%
Held-to-maturity amount after ten years	356
Held-to-maturity yield after ten years	6.19%
Obligations of U.S. states and political subdivisions [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount after one but within five years	31
Available-for-sale yield after one but within five years	4.20%
Available-for-sale amount after five but within ten years	291
Available-for-sale yield after five but within ten years	4.24%
Available-for-sale amount after ten years	324
Available-for-sale yield after ten years	3.92%
Held-to-maturity amount within one year	4
Held-to-maturity yield within one year	5.73%
Held-to-maturity amount after one but within five years	16
Held-to-maturity yield after one but within five years	3.64%
Held-to-maturity amount after five but within ten years	10
Held-to-maturity yield after five but within ten years	2.80%
Held-to-maturity amount after ten years	17
Held-to-maturity yield after ten years	3.82%
Asset-backed Securities [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount after one but within five years	1
Available-for-sale yield after one but within five years	1.41%
Available-for-sale amount after five but within ten years	22
Available-for-sale yield after five but within ten years	0.66%
Available-for-sale amount after ten years	731
Available-for-sale yield after ten years	3.13%
Held-to-maturity amount after ten years	146
Corporate and other domestic [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount within one year	16
Available-for-sale yield within one year	0.71%
Available-for-sale amount after ten years	24
Available-for-sale yield after ten years	3.90%
Foreign debt securities [Member]
Distribution of maturities of debt securities with the approximate yield of the portfolio
Available-for-sale amount within one year	1,274
Available-for-sale yield within one year	2.84%
Available-for-sale amount after one but within five years	$ 5,595
Available-for-sale yield after one but within five years	1.90%