Debt Notes and Debentures (Details) (USD $)																	0 Months Ended	1 Months Ended
	Dec. 31, 2013		Dec. 31, 2013 Mortgage Bonds [Member]		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]	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 [Member]	Aug. 31, 2011 Corporate Debt Securities Three Point Four Five Percent Debentures Due September 15, 2021 [Member]	Aug. 31, 2011 Corporate Debt Securities Four Point Nine Five Percent Debentures Due September 15, 2041 [Member]	May 31, 2011 Corporate Debt Securities Four Point One Zero Percent Debentures Due June 1, 2021 [Member]	May 31, 2011 Corporate Debt Securities Five Point Four Zero Percent Debentures Due June 1, 2041 [Member]	Jul. 31, 2013 SEC Debt Shelf Registration	Jan. 31, 2013 SEC Debt Shelf Registration	Dec. 31, 2013 SEC Debt Shelf Registration	Dec. 31, 2013 Junior Subordinated Debt
Debt Instrument [Line Items]
Debentures issued amount					$ 800,000,000	$ 700,000,000	$ 700,000,000	$ 800,000,000	$ 600,000,000	$ 650,000,000	$ 625,000,000	$ 625,000,000	$ 450,000,000	$ 300,000,000	$ 250,000,000	$ 500,000,000
Debentures interest rate					3.85%	5.15%	3.00%	4.45%	3.05%	4.375%	3.05%	4.40%	3.45%	4.95%	4.10%	5.40%
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
Total Debt excluding capital leases	$ 16,066,000,000	[1],[2]	$ 82,000,000	[3]

[1] Amount also excludes unamortized fair value adjustment under acquisition method accounting related to capital leases.

[2] Amount also excludes unamortized gains on interest rate swaps.

[3] Amounts represent debt outstanding and weighted average effective interest rates for 2013 and 2012, respectively. Maturities are as of December 31, 2013.