Debt Notes and Debentures (Details) (USD $)					0 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	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	Jan. 31, 2012 SEC Debt Shelf Registration	Jun. 30, 2012 SEC Debt Shelf Registration	Jun. 30, 2012 Junior Subordinated Debt
Debt Instrument [Line Items]
Debentures issued amount			$ 625,000,000	$ 625,000,000
Debentures interest rate			3.05%	4.40%
Additional debt securities authorized for issuance by the Board of Managers					1,500,000,000
Remaining amount of debt securities that may be issued						1,000,000,000
Subordintaed notes related to financial covenants							500,000,000
Debt, fair value	14,068,000,000	12,947,000,000
Debt, book value	$ 12,568,000,000	$ 11,395,000,000