Investments in Securities Other-than-temporary Impairments 4 (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 7,431
Weighted average collateral default	52.70%	[1]
Weighted average collateral severities	59.50%	[2]
Weighted average voluntary prepayment rates	2.50%	[3]
Average credit enhancement	10.90%	[4]
Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,204
Weighted average collateral default	36.10%	[1]
Weighted average collateral severities	49.60%	[2]
Weighted average voluntary prepayment rates	7.10%	[3]
Average credit enhancement	4.70%	[4]
Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,060
Weighted average collateral default	17.30%	[1]
Weighted average collateral severities	54.10%	[2]
Weighted average voluntary prepayment rates	11.10%	[3]
Average credit enhancement	5.00%	[4]
Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,306
Weighted average collateral default	33.70%	[1]
Weighted average collateral severities	46.50%	[2]
Weighted average voluntary prepayment rates	8.10%	[3]
Average credit enhancement	5.60%	[4]
Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,742
Weighted average collateral default	21.20%	[1]
Weighted average collateral severities	43.60%	[2]
Weighted average voluntary prepayment rates	9.60%	[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	114
Weighted average collateral default	26.50%	[1]
Weighted average collateral severities	55.20%	[2]
Weighted average voluntary prepayment rates	9.50%	[3]
Average credit enhancement	38.20%	[4]
2004 and Prior [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	113
Weighted average collateral default	23.90%	[1]
Weighted average collateral severities	54.70%	[2]
Weighted average voluntary prepayment rates	9.80%	[3]
Average credit enhancement	3.90%	[4]
2004 and Prior [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	879
Weighted average collateral default	9.50%	[1]
Weighted average collateral severities	52.80%	[2]
Weighted average voluntary prepayment rates	13.10%	[3]
Average credit enhancement	11.00%	[4]
2004 and Prior [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	126
Weighted average collateral default	21.40%	[1]
Weighted average collateral severities	40.50%	[2]
Weighted average voluntary prepayment rates	9.60%	[3]
Average credit enhancement	22.40%	[4]
2004 and Prior [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	316
Weighted average collateral default	14.10%	[1]
Weighted average collateral severities	38.50%	[2]
Weighted average voluntary prepayment rates	10.20%	[3]
Average credit enhancement	9.40%	[4]
2005 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	10
Weighted average collateral default	49.20%	[1]
Weighted average collateral severities	63.30%	[2]
Weighted average voluntary prepayment rates	4.10%	[3]
Average credit enhancement	58.80%	[4]
2005 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	460
Weighted average collateral default	31.20%	[1]
Weighted average collateral severities	53.10%	[2]
Weighted average voluntary prepayment rates	7.70%	[3]
Average credit enhancement	8.10%	[4]
2005 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	797
Weighted average collateral default	22.40%	[1]
Weighted average collateral severities	53.90%	[2]
Weighted average voluntary prepayment rates	10.30%	[3]
Average credit enhancement	0.70%	[4]
2005 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	285
Weighted average collateral default	33.40%	[1]
Weighted average collateral severities	48.20%	[2]
Weighted average voluntary prepayment rates	8.40%	[3]
Average credit enhancement	12.80%	[4]
2005 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,272
Weighted average collateral default	26.40%	[1]
Weighted average collateral severities	44.00%	[2]
Weighted average voluntary prepayment rates	9.00%	[3]
Average credit enhancement	2.80%	[4]
2006 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	6,973
Weighted average collateral default	53.20%	[1]
Weighted average collateral severities	61.00%	[2]
Weighted average voluntary prepayment rates	2.40%	[3]
Average credit enhancement	9.90%	[4]
2006 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	631
Weighted average collateral default	41.80%	[1]
Weighted average collateral severities	47.10%	[2]
Weighted average voluntary prepayment rates	6.20%	[3]
Average credit enhancement	2.20%	[4]
2006 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	384
Weighted average collateral default	24.40%	[1]
Weighted average collateral severities	55.60%	[2]
Weighted average voluntary prepayment rates	8.20%	[3]
Average credit enhancement	0.10%	[4]
2006 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	895
Weighted average collateral default	35.50%	[1]
Weighted average collateral severities	46.50%	[2]
Weighted average voluntary prepayment rates	7.70%	[3]
Average credit enhancement	0.90%	[4]
2006 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,074
Weighted average collateral default	17.00%	[1]
Weighted average collateral severities	44.40%	[2]
Weighted average voluntary prepayment rates	10.20%	[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	334
Weighted average collateral default	50.30%	[1]
Weighted average collateral severities	27.50%	[2]
Weighted average voluntary prepayment rates	1.40%	[3]
Average credit enhancement	19.90%	[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	$ 80
Weighted average collateral default	22.10%	[1]
Weighted average collateral severities	39.60%	[2]
Weighted average voluntary prepayment rates	9.60%	[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.