Investments in Securities Other-than-temporary Impairments 4 (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 10,642
Weighted average collateral default	56.70%	[1]
Weighted average collateral severities	62.50%	[2]
Weighted average voluntary prepayment rates	2.40%	[3]
Average credit enhancement	14.00%	[4]
Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,896
Weighted average collateral default	40.80%	[1]
Weighted average collateral severities	52.90%	[2]
Weighted average voluntary prepayment rates	6.20%	[3]
Average credit enhancement	7.00%	[4]
Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,378
Weighted average collateral default	18.90%	[1]
Weighted average collateral severities	54.30%	[2]
Weighted average voluntary prepayment rates	10.10%	[3]
Average credit enhancement	5.20%	[4]
Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,774
Weighted average collateral default	39.30%	[1]
Weighted average collateral severities	48.80%	[2]
Weighted average voluntary prepayment rates	7.20%	[3]
Average credit enhancement	5.30%	[4]
Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	3,419
Weighted average collateral default	24.40%	[1]
Weighted average collateral severities	43.50%	[2]
Weighted average voluntary prepayment rates	8.60%	[3]
Average credit enhancement	3.00%	[4]
2004 and Prior [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	452
Weighted average collateral default	30.70%	[1]
Weighted average collateral severities	55.80%	[2]
Weighted average voluntary prepayment rates	7.30%	[3]
Average credit enhancement	47.20%	[4]
2004 and Prior [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	215
Weighted average collateral default	25.30%	[1]
Weighted average collateral severities	52.40%	[2]
Weighted average voluntary prepayment rates	8.10%	[3]
Average credit enhancement	5.50%	[4]
2004 and Prior [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,048
Weighted average collateral default	10.10%	[1]
Weighted average collateral severities	51.40%	[2]
Weighted average voluntary prepayment rates	11.80%	[3]
Average credit enhancement	11.20%	[4]
2004 and Prior [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	178
Weighted average collateral default	22.00%	[1]
Weighted average collateral severities	41.10%	[2]
Weighted average voluntary prepayment rates	8.60%	[3]
Average credit enhancement	20.10%	[4]
2004 and Prior [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	592
Weighted average collateral default	15.40%	[1]
Weighted average collateral severities	37.30%	[2]
Weighted average voluntary prepayment rates	8.70%	[3]
Average credit enhancement	6.70%	[4]
2005 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	51
Weighted average collateral default	54.10%	[1]
Weighted average collateral severities	61.60%	[2]
Weighted average voluntary prepayment rates	2.70%	[3]
Average credit enhancement	49.30%	[4]
2005 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	827
Weighted average collateral default	38.00%	[1]
Weighted average collateral severities	55.90%	[2]
Weighted average voluntary prepayment rates	6.60%	[3]
Average credit enhancement	8.70%	[4]
2005 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	906
Weighted average collateral default	25.20%	[1]
Weighted average collateral severities	54.70%	[2]
Weighted average voluntary prepayment rates	9.50%	[3]
Average credit enhancement	0.50%	[4]
2005 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	425
Weighted average collateral default	37.80%	[1]
Weighted average collateral severities	47.30%	[2]
Weighted average voluntary prepayment rates	7.60%	[3]
Average credit enhancement	12.10%	[4]
2005 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,448
Weighted average collateral default	30.40%	[1]
Weighted average collateral severities	44.80%	[2]
Weighted average voluntary prepayment rates	8.20%	[3]
Average credit enhancement	3.10%	[4]
2006 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	9,656
Weighted average collateral default	58.10%	[1]
Weighted average collateral severities	63.40%	[2]
Weighted average voluntary prepayment rates	2.30%	[3]
Average credit enhancement	11.80%	[4]
2006 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	854
Weighted average collateral default	47.40%	[1]
Weighted average collateral severities	50.70%	[2]
Weighted average voluntary prepayment rates	5.30%	[3]
Average credit enhancement	5.70%	[4]
2006 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	424
Weighted average collateral default	27.30%	[1]
Weighted average collateral severities	56.40%	[2]
Weighted average voluntary prepayment rates	7.20%	[3]
Average credit enhancement	0.10%	[4]
2006 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,171
Weighted average collateral default	42.50%	[1]
Weighted average collateral severities	49.90%	[2]
Weighted average voluntary prepayment rates	6.90%	[3]
Average credit enhancement	0.70%	[4]
2006 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,288
Weighted average collateral default	21.80%	[1]
Weighted average collateral severities	43.40%	[2]
Weighted average voluntary prepayment rates	8.90%	[3]
Average credit enhancement	0.00%	[4]
2007 and After [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	483
Weighted average collateral default	53.80%	[1]
Weighted average collateral severities	47.70%	[2]
Weighted average voluntary prepayment rates	1.60%	[3]
Average credit enhancement	24.00%	[4]
2007 and After [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	0
2007 and After [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	0
2007 and After [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	0
2007 and After [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 91
Weighted average collateral default	24.60%	[1]
Weighted average collateral severities	44.30%	[2]
Weighted average voluntary prepayment rates	8.30%	[3]
Average credit enhancement	20.50%	[4]

[1] The expected remaining cumulative default rate of the collateral pool backing the securities, as a percentage of the current collateral unpaid principal balance, weighted by security unpaid principal balance.

[2] The expected remaining loss given default of the collateral pool backing the securities, calculated as the ratio of remaining cumulative loss divided by cumulative defaults, weighted by security unpaid principal balance.

[3] The average monthly voluntary prepayment rate, weighted by security unpaid principal balance.

[4] The average percent current credit enhancement provided by subordination of other securities. Excludes excess interest projections and monoline bond insurance.