Investments (Details 6) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	$ 170,097	$ 159,660
% of Total	100.00%	100.00%
RMBS [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	41,893	44,733
% of Total	100.00%	100.00%
RMBS [Member] \| Pass-through securities [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	18,990	22,430
% of Total	45.30%	50.10%
RMBS [Member] \| Collateralized mortgage obligations [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	22,903	22,303
% of Total	54.70%	49.90%
RMBS [Member] \| Agency [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	31,386	34,254
% of Total	74.90%	76.60%
RMBS [Member] \| Residential, Prime, Financing Receivable [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	5,935	6,258
% of Total	14.20%	14.00%
RMBS [Member] \| Alternative residential mortgage loans [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	4,572	4,221
% of Total	10.90%	9.40%
RMBS [Member] \| Aaa [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	32,452	36,085
% of Total	77.50%	80.70%
RMBS [Member] \| NAIC 1 [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	36,543	38,984
% of Total	87.20%	87.10%
Alternative residential mortgage loans [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Estimated fair value	$ 4,572	$ 4,221
% of Total	100.00%	100.00%
Alternative residential mortgage loans [Member] \| NAIC 1 [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
% of Total	47.10%	39.50%

This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 15A

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 15C

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 107

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 1

-Subparagraph a, f, g

+ Details