Investments (Details 45) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	$ 366,339	$ 350,271
Mortgage Loans on Real Estate, Commercial and Consumer, Net	57,201	56,915
Estimated Fair Value	6,932	7,273
MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	49	49
Cash and cash equivalents	45	59
Estimated Fair Value	3,383	3,333
Fixed maturity securities [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	366,339	350,271
U.S. corporate securities [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	110,373	105,785
U.S. corporate securities [Member] \| MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	891	833
Foreign corporate securities [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	63,345	64,018
Foreign corporate securities [Member] \| MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	125	126
RMBS [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	41,064	42,637
RMBS [Member] \| MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	483	502
CMBS [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	19,017	19,069
CMBS [Member] \| MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	300	369
ABS [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	13,892	12,979
ABS [Member] \| MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	1,456	1,356
State and political subdivision securities [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	14,614	13,235
State and political subdivision securities [Member] \| MRSC collateral financing arrangement [Member]
Variable Interest Entity [Line Items]
Available-for-sale Securities, Debt Securities	$ 34	$ 39

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-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 FASB Staff Position (FSP)

-Number FAS115-1/124-1

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-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 6: 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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 320

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

-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 FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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

+ Details

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

+ References+ Details