Debt Notes and Debentures (Details) (USD $)					0 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012 Corporate Debt Securities Three Point Zero Percent Debentures Due March 15, 2023 [Member]	Mar. 31, 2012 Corporate Debt Securities Four Point Four Five Percent Debentures Due March 15, 2043 [Member]	Jan. 31, 2012 SEC Debt Shelf Registration	Mar. 31, 2013 SEC Debt Shelf Registration	Mar. 31, 2013 Junior Subordinated Debt
Debt Instrument [Line Items]
Debentures issued amount			$ 700,000,000	$ 800,000,000
Debentures interest rate			3.00%	4.45%
Additional debt securities authorized for issuance by the Board of Managers					1,000,000,000
Remaining amount of debt securities that may be issued						250,000,000
Subordinated notes related to financial covenants							500,000,000
Debt, fair value	16,552,000,000	15,291,000,000
Debt, book value	$ 14,908,000,000	$ 13,455,000,000