Investments in Securities Other-than-temporary Impairments 4 (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	$ 13,280
Weighted average collateral default	67.70%	[1]
Weighted average collateral severities	77.00%	[2]
Weighted average voluntary prepayment rates	2.70%	[3]
Average credit enhancement	20.80%	[4]
Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,779
Weighted average collateral default	58.10%	[1]
Weighted average collateral severities	67.20%	[2]
Weighted average voluntary prepayment rates	4.10%	[3]
Average credit enhancement	18.50%	[4]
Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	4,690
Weighted average collateral default	22.30%	[1]
Weighted average collateral severities	58.70%	[2]
Weighted average voluntary prepayment rates	9.70%	[3]
Average credit enhancement	8.30%	[4]
Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,446
Weighted average collateral default	51.60%	[1]
Weighted average collateral severities	62.40%	[2]
Weighted average voluntary prepayment rates	4.50%	[3]
Average credit enhancement	7.70%	[4]
Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	5,954
Weighted average collateral default	31.10%	[1]
Weighted average collateral severities	53.40%	[2]
Weighted average voluntary prepayment rates	6.80%	[3]
Average credit enhancement	5.80%	[4]
2004 and Prior [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,518
Weighted average collateral default	41.00%	[1]
Weighted average collateral severities	70.20%	[2]
Weighted average voluntary prepayment rates	6.30%	[3]
Average credit enhancement	51.30%	[4]
2004 and Prior [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	460
Weighted average collateral default	39.90%	[1]
Weighted average collateral severities	60.50%	[2]
Weighted average voluntary prepayment rates	5.70%	[3]
Average credit enhancement	13.60%	[4]
2004 and Prior [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	3,101
Weighted average collateral default	13.30%	[1]
Weighted average collateral severities	54.70%	[2]
Weighted average voluntary prepayment rates	11.30%	[3]
Average credit enhancement	12.10%	[4]
2004 and Prior [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	459
Weighted average collateral default	30.30%	[1]
Weighted average collateral severities	53.50%	[2]
Weighted average voluntary prepayment rates	6.00%	[3]
Average credit enhancement	22.90%	[4]
2004 and Prior [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,107
Weighted average collateral default	17.80%	[1]
Weighted average collateral severities	47.80%	[2]
Weighted average voluntary prepayment rates	8.90%	[3]
Average credit enhancement	10.00%	[4]
2005 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	155
Weighted average collateral default	68.40%	[1]
Weighted average collateral severities	76.30%	[2]
Weighted average voluntary prepayment rates	2.30%	[3]
Average credit enhancement	65.50%	[4]
2005 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,235
Weighted average collateral default	54.80%	[1]
Weighted average collateral severities	67.80%	[2]
Weighted average voluntary prepayment rates	4.40%	[3]
Average credit enhancement	22.30%	[4]
2005 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,097
Weighted average collateral default	39.70%	[1]
Weighted average collateral severities	66.10%	[2]
Weighted average voluntary prepayment rates	6.80%	[3]
Average credit enhancement	1.00%	[4]
2005 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	499
Weighted average collateral default	52.30%	[1]
Weighted average collateral severities	64.40%	[2]
Weighted average voluntary prepayment rates	4.90%	[3]
Average credit enhancement	14.90%	[4]
2005 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	2,191
Weighted average collateral default	38.80%	[1]
Weighted average collateral severities	55.40%	[2]
Weighted average voluntary prepayment rates	5.60%	[3]
Average credit enhancement	4.90%	[4]
2006 [Member] | Subprime private-label securities [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	11,025
Weighted average collateral default	71.40%	[1]
Weighted average collateral severities	78.20%	[2]
Weighted average voluntary prepayment rates	2.20%	[3]
Average credit enhancement	15.40%	[4]
2006 [Member] | Alt-A Option ARM [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,084
Weighted average collateral default	69.60%	[1]
Weighted average collateral severities	69.20%	[2]
Weighted average voluntary prepayment rates	3.10%	[3]
Average credit enhancement	16.20%	[4]
2006 [Member] | Alt-A Fixed Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	492
Weighted average collateral default	40.50%	[1]
Weighted average collateral severities	67.50%	[2]
Weighted average voluntary prepayment rates	5.60%	[3]
Average credit enhancement	0.50%	[4]
2006 [Member] | Alt-A Variable Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,488
Weighted average collateral default	57.90%	[1]
Weighted average collateral severities	64.40%	[2]
Weighted average voluntary prepayment rates	3.80%	[3]
Average credit enhancement	0.70%	[4]
2006 [Member] | Alt-A Hybrid Rate [Member]
UPB and Modeled Attributes [Line Items]
Unpaid principal balance	1,548
Weighted average collateral default	37.40%	[1]
Weighted average collateral severities	57.90%	[2]
Weighted average voluntary prepayment rates	5.50%	[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	582
Weighted average collateral default	67.70%	[1]
Weighted average collateral severities	71.40%	[2]
Weighted average voluntary prepayment rates	1.90%	[3]
Average credit enhancement	31.30%	[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	$ 108
Weighted average collateral default	40.90%	[1]
Weighted average collateral severities	59.90%	[2]
Weighted average voluntary prepayment rates	6.50%	[3]
Average credit enhancement	24.40%	[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.