Debt Notes and Debentures (Details) (USD $)							0 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Aug. 31, 2012 Corporate Debt Securities Three Point Zero Five Percent Debentures Due September 1, 2022 [Member]	Aug. 31, 2012 Corporate Debt Securities Four Point Three Seven Five Percent Debentures Due September 1, 2042 [Member]	Mar. 31, 2012 Corporate Debt Securities Three Point Zero Five Percent Debentures Due March 15, 2022	Mar. 31, 2012 Corporate Debt Securities Four Point Four Zero Percent Debentures Due March 15, 2042	Jul. 31, 2012 SEC Debt Shelf Registration	Jan. 31, 2012 SEC Debt Shelf Registration	Sep. 30, 2012 SEC Debt Shelf Registration	Sep. 30, 2012 Junior Subordinated Debt
Debt Instrument [Line Items]
Debentures issued amount			$ 600,000,000	$ 650,000,000	$ 625,000,000	$ 625,000,000
Debentures interest rate			3.05%	4.375%	3.05%	4.40%
Additional debt securities authorized for issuance by the Board of Managers							1,000,000,000	1,500,000,000
Remaining amount of debt securities that may be issued									750,000,000
Subordinated notes related to financial covenants										500,000,000
Debt, fair value	15,483,000,000	12,947,000,000
Debt, book value	$ 13,480,000,000	$ 11,395,000,000