Debt Notes and Debentures (Details) (USD $)							0 Months Ended	1 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Aug. 31, 2013 Corporate Debt Securities Three Point Eight Five Zero Percent Debentures Due September 1, 2023 [Member]	Aug. 31, 2013 Corporate Debt Securities Five Point One Five Zero Percent Debentures Due September 1, 2043 [Member]	Mar. 31, 2013 Corporate Debt Securities Three Point Zero Percent Debentures Due March 15, 2023 [Member]	Mar. 31, 2013 Corporate Debt Securities Four Point Four Five Percent Debentures Due March 15, 2043 [Member]	Jul. 31, 2013 SEC Debt Shelf Registration	Jan. 31, 2013 SEC Debt Shelf Registration	Sep. 30, 2013 SEC Debt Shelf Registration	Sep. 30, 2013 Junior Subordinated Debt
Debt Instrument [Line Items]
Debentures issued amount			$ 800,000,000	$ 700,000,000	$ 700,000,000	$ 800,000,000
Debentures interest rate			3.85%	5.15%	3.00%	4.45%
Additional debt securities authorized for issuance by the Board of Managers							3,000,000,000	1,000,000,000
Remaining amount of debt securities that may be issued									1,750,000,000
Subordinated notes related to financial covenants										500,000,000
Debt, fair value	16,730,000,000	15,291,000,000
Debt, book value	$ 16,089,000,000	$ 13,455,000,000