Investments in Securities Other-than-temporary Impairments 4 (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 10,201
Weighted average collateral default	53.20%	[1]
Weighted average collateral severities	61.00%	[2]
Weighted average voluntary prepayment rates	2.50%	[3]
Average credit enhancement	12.00%	[4]
Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,817
Weighted average collateral default	38.00%	[1]
Weighted average collateral severities	51.50%	[2]
Weighted average voluntary prepayment rates	6.60%	[3]
Average credit enhancement	5.10%	[4]
Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,229
Weighted average collateral default	18.20%	[1]
Weighted average collateral severities	54.00%	[2]
Weighted average voluntary prepayment rates	10.40%	[3]
Average credit enhancement	5.10%	[4]
Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,683
Weighted average collateral default	35.90%	[1]
Weighted average collateral severities	47.80%	[2]
Weighted average voluntary prepayment rates	7.60%	[3]
Average credit enhancement	5.50%	[4]
Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	3,246
Weighted average collateral default	22.30%	[1]
Weighted average collateral severities	43.40%	[2]
Weighted average voluntary prepayment rates	9.00%	[3]
Average credit enhancement	2.80%	[4]
2004 and Prior [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	437
Weighted average collateral default	29.60%	[1]
Weighted average collateral severities	55.70%	[2]
Weighted average voluntary prepayment rates	7.30%	[3]
Average credit enhancement	46.40%	[4]
2004 and Prior [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	207
Weighted average collateral default	24.20%	[1]
Weighted average collateral severities	52.70%	[2]
Weighted average voluntary prepayment rates	8.30%	[3]
Average credit enhancement	4.40%	[4]
2004 and Prior [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	967
Weighted average collateral default	10.10%	[1]
Weighted average collateral severities	51.90%	[2]
Weighted average voluntary prepayment rates	12.10%	[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	163
Weighted average collateral default	20.00%	[1]
Weighted average collateral severities	40.70%	[2]
Weighted average voluntary prepayment rates	8.60%	[3]
Average credit enhancement	21.60%	[4]
2004 and Prior [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	552
Weighted average collateral default	14.20%	[1]
Weighted average collateral severities	36.70%	[2]
Weighted average voluntary prepayment rates	9.00%	[3]
Average credit enhancement	6.50%	[4]
2005 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	44
Weighted average collateral default	50.50%	[1]
Weighted average collateral severities	60.70%	[2]
Weighted average voluntary prepayment rates	2.80%	[3]
Average credit enhancement	48.40%	[4]
2005 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	800
Weighted average collateral default	35.70%	[1]
Weighted average collateral severities	54.60%	[2]
Weighted average voluntary prepayment rates	7.10%	[3]
Average credit enhancement	6.90%	[4]
2005 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	858
Weighted average collateral default	23.90%	[1]
Weighted average collateral severities	54.00%	[2]
Weighted average voluntary prepayment rates	9.70%	[3]
Average credit enhancement	0.60%	[4]
2005 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	405
Weighted average collateral default	34.70%	[1]
Weighted average collateral severities	47.40%	[2]
Weighted average voluntary prepayment rates	7.90%	[3]
Average credit enhancement	12.40%	[4]
2005 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,382
Weighted average collateral default	27.90%	[1]
Weighted average collateral severities	44.50%	[2]
Weighted average voluntary prepayment rates	8.60%	[3]
Average credit enhancement	2.90%	[4]
2006 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	9,252
Weighted average collateral default	54.50%	[1]
Weighted average collateral severities	62.30%	[2]
Weighted average voluntary prepayment rates	2.30%	[3]
Average credit enhancement	9.60%	[4]
2006 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	810
Weighted average collateral default	43.80%	[1]
Weighted average collateral severities	48.80%	[2]
Weighted average voluntary prepayment rates	5.60%	[3]
Average credit enhancement	3.50%	[4]
2006 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	404
Weighted average collateral default	25.20%	[1]
Weighted average collateral severities	55.80%	[2]
Weighted average voluntary prepayment rates	7.80%	[3]
Average credit enhancement	0.10%	[4]
2006 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,115
Weighted average collateral default	38.70%	[1]
Weighted average collateral severities	48.40%	[2]
Weighted average voluntary prepayment rates	7.40%	[3]
Average credit enhancement	0.60%	[4]
2006 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,227
Weighted average collateral default	19.60%	[1]
Weighted average collateral severities	44.00%	[2]
Weighted average voluntary prepayment rates	9.50%	[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	468
Weighted average collateral default	51.10%	[1]
Weighted average collateral severities	38.20%	[2]
Weighted average voluntary prepayment rates	1.60%	[3]
Average credit enhancement	22.80%	[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	$ 85
Weighted average collateral default	23.00%	[1]
Weighted average collateral severities	41.40%	[2]
Weighted average voluntary prepayment rates	8.90%	[3]
Average credit enhancement	20.20%	[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.