Debt (Details) (USD $)			0 Months Ended	9 Months Ended	0 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Feb. 20, 2014 Facility	Sep. 30, 2014 Facility	Feb. 20, 2014 Facility Minimum	Feb. 20, 2014 Facility Maximum	Feb. 20, 2014 Term loan	Feb. 20, 2014 Commercial paper	Jun. 12, 2014 4.55% first mortgage bonds, Series 2014A
Debt
Aggregate borrowings expressed as a percentage of Eligible Project Costs						70.00%
Aggregate borrowings						$ 3,057,069,461
Capitalized interest			335,471,604
Principal amount			725,000,000	35,900,000					250,000,000
Total investment	4,577,424,000	4,434,728,000
Fixed interest rate (as a percent)			3.867%
Repayment of outstanding debt							260,000,000	465,000,000
Term of each advance					3 months
Interest accrued and payable through November 20, 2019, is reflected as additional borrowings under the Facility						335,471,604
Amount of interest reflected as long-term debt on the condensed balance sheet				17,179,000
Basis spread (as a percent)			0.375%
Issuance costs			$ 51,000,000
Interest rate (as a percent)									4.55%