Investments (Details 43) (USD $) In Millions	6 Months Ended	12 Months Ended
Jun. 30, 2011	Dec. 31, 2010
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	$ 341,744	$ 324,797
Fixed maturity securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	341,744	324,797
MRSC collateral financing arrangement [Member] \| U.S. corporate securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	745	893
U.S. corporate securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	96,797	91,772
MRSC collateral financing arrangement [Member] \| RMBS [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	547	547
RMBS [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	43,550	44,733
MRSC collateral financing arrangement [Member] \| U.S. Treasury, agency and government guaranteed securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	0	0
U.S. Treasury, agency and government guaranteed securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	35,565	33,304
MRSC collateral financing arrangement [Member] \| ABS [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	1,447	1,333
ABS [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	14,857	14,287
MRSC collateral financing arrangement [Member] \| State and political subdivision securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	40	30
State and political subdivision securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	11,669	10,129
MRSC collateral financing arrangement [Member] \| Foreign government debt securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	0	5
MRSC collateral financing arrangement [Member] \| Foreign corporate securities [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	166	139
MRSC collateral financing arrangement [Member] \| Cash and cash equivalents (including cash held in trust of less than $0 million and $1 million, respectively) [Member]
Variable Interest Entity Primary Beneficiary
Cash and cash equivalents	24	3
MRSC collateral financing arrangement [Member] \| CMBS [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	412	383
CMBS [Member]
Variable Interest Entity Primary Beneficiary
Available-for-sale Securities, Debt Securities	19,518	20,675
MRSC collateral financing arrangement [Member]
Variable Interest Entity Primary Beneficiary
Estimated Fair Value	$ 3,381	$ 3,333

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading. Such securities are reported at fair value; unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income, a separate component of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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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.

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- Definition

The carrying amount of the variable interest entity's assets consolidated into the statement of financial position. In general, a VIE is a corporation, partnership, trust, or any other legal structure used for business purposes that either (a) does not have equity investors with voting rights or (b) has equity investors that do not provide sufficient financial resources for the entity to support its activities. A VIE often holds financial assets, including loans or receivables, real estate or other property. A VIE may be essentially passive or it may engage in research and development or other activities on behalf of another company.

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