Debt and Credit Agreements (Debt Covenants) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 High Lonesome Mesa, LLC		Dec. 31, 2013 Viento Funding II, Inc.		Dec. 31, 2013 Tapestry Wind, LLC		Dec. 31, 2013 Laredo Ridge		Dec. 31, 2013 Cedro Hill Wind, LLC		Dec. 31, 2013 Broken Bow I LLC [Member]		Dec. 31, 2013 Crofton Bluffs		Dec. 31, 2013 Walnut Creek Energy [Member]		Dec. 31, 2013 American Bituminous		Dec. 31, 2013 EME Subsidiaries	Dec. 31, 2013 WCEP Holdings, LLC		Dec. 31, 2013 Term Loan Due 2023 Viento Funding II, Inc.	Dec. 31, 2012 Term Loan Due 2023 Viento Funding II, Inc.	Dec. 31, 2013 Construction Loan Term Loan Due 2023 Walnut Creek	Jun. 01, 2013 Construction Loan Term Loan Due 2023 Walnut Creek	Dec. 31, 2012 Construction Loan Term Loan Due 2023 Walnut Creek	Dec. 31, 2013 Construction Loan Term Loan Due 2023 WCEP Holdings, LLC	Dec. 31, 2012 Construction Loan Term Loan Due 2023 WCEP Holdings, LLC
Debt Instrument [Line Items]
Debt	$ 1,498,000,000	$ 1,438,000,000																						$ 200,000,000	$ 191,000,000	$ 417,000,000	$ 495,000,000	$ 330,000,000	$ 53,000,000	$ 52,000,000
Restriction on Net Assets																					1,700,000,000
Required debt service coverage ratio			1.20	[1]	1.20	[1]	1.20	[1]	1.20	[1]	1.20	[1]	1.20	[1]	1.20	[1]	1.20	[1]				2.5	[1]
Actual debt service coverage ratio			1.88	[1],[2]	2.75	[1]	1.48	[1]	1.79	[1]	1.53	[1]	1.67	[1]	2.23	[1]
Required reserve																			20,000,000	[3]
Required reserve, funded status																			$ 4,000,000	[3]
Period of debt service coverage ratio (months)	12 months

[1] The Debt Service Coverage Ratio (DSCR) is typically calculated over a 12-month historical period and is individually defined for each borrowing in the applicable financing agreement, credit agreement, trust indenture, or other document governing the financing requirements.

[2] Calculated at October 31, 2013, the last payment date.

[3] Ambit is required to maintain funded reserve accounts primarily for debt servicing and maintenance costs. The underfunded reserve does not create an event of default under the loan but does restrict distributions from Ambit.