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 represents investments accounted for under the cost method of accounting as of the balance sheet date.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the cost method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Fair Value (Nonrecurring Fair Value Measurements) (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended				3 Months Ended				3 Months Ended				3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Non Recurring [Member] Real Estate Funds [Member]	Mar. 31, 2012 Non Recurring [Member] Real Estate Funds [Member]	Mar. 31, 2013 Non Recurring [Member] Real Estate Funds [Member] Level 3 [Member]	Mar. 31, 2012 Non Recurring [Member] Real Estate Funds [Member] Level 3 [Member]	Mar. 31, 2013 Non Recurring [Member] Held-for-investments [Member]	Mar. 31, 2012 Non Recurring [Member] Held-for-investments [Member]	Mar. 31, 2013 Non Recurring [Member] Held-for-investments [Member] Level 3 [Member]	Mar. 31, 2012 Non Recurring [Member] Held-for-investments [Member] Level 3 [Member]	Mar. 31, 2013 Non Recurring [Member] Held-for-sale [Member]	Mar. 31, 2012 Non Recurring [Member] Held-for-sale [Member]	Mar. 31, 2013 Non Recurring [Member] Held-for-sale [Member] Level 3 [Member]	Mar. 31, 2012 Non Recurring [Member] Held-for-sale [Member] Level 3 [Member]	Mar. 31, 2013 Non Recurring [Member] Other limited partnership interests [Member]	Mar. 31, 2012 Non Recurring [Member] Other limited partnership interests [Member]	Mar. 31, 2013 Non Recurring [Member] Other limited partnership interests [Member] Level 3 [Member]	Mar. 31, 2012 Non Recurring [Member] Other limited partnership interests [Member] Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value Prior to Measurement			$ 5	$ 5			$ 248	$ 166			$ 288	$ 320			$ 1	$ 10
Carrying Value After Measurement									255	167
Mortgage loans held-for-sale	2	49											267	304
Carrying Value After Measurement					3	2											1	7
Gain (Losses)							7	1			(21)	(16)
Gain (Losses)			$ (2)	$ (3)											$ 0	$ (3)