Derivative Instruments and Hedging Activities (Interest Rate Risk Management) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended
	Jul. 11, 2013 Interest rate contracts	Dec. 31, 2013 Interest rate contracts	Dec. 31, 2013 Viento Funding II, Inc. Interest rate contracts Swap 1	Dec. 31, 2012 Viento Funding II, Inc. Interest rate contracts Swap 1	Dec. 31, 2013 Viento Funding II, Inc. Interest rate contracts Swap 2	Dec. 31, 2012 Viento Funding II, Inc. Interest rate contracts Swap 2	Dec. 31, 2013 Viento Funding II, Inc. Interest rate contracts Swap 3 [Member]	Dec. 31, 2012 Viento Funding II, Inc. Interest rate contracts Swap 3 [Member]	Dec. 31, 2013 Viento Funding II, Inc. Forward Starting Interest Rate Contracts	Dec. 31, 2012 Viento Funding II, Inc. Forward Starting Interest Rate Contracts	Dec. 31, 2013 Cedro Hill Wind, LLC Interest rate contracts	Dec. 31, 2012 Cedro Hill Wind, LLC Interest rate contracts	Dec. 31, 2013 Laredo Ridge Interest rate contracts	Dec. 31, 2012 Laredo Ridge Interest rate contracts	Dec. 31, 2013 Tapestry Wind, LLC Interest rate contracts	Dec. 31, 2012 Tapestry Wind, LLC Interest rate contracts	Dec. 31, 2013 Tapestry Wind, LLC Forward Starting Interest Rate Contracts	Dec. 31, 2012 Tapestry Wind, LLC Forward Starting Interest Rate Contracts	Dec. 31, 2013 Broken Bow Wind, LLC Interest rate contracts		Dec. 31, 2012 Broken Bow Wind, LLC Interest rate contracts		Dec. 31, 2013 Broken Bow Wind, LLC Expired Interest Rate Contracts [Member]		Dec. 31, 2012 Broken Bow Wind, LLC Expired Interest Rate Contracts [Member]		Dec. 31, 2013 Crofton Bluffs Interest rate contracts		Dec. 31, 2012 Crofton Bluffs Interest rate contracts		Dec. 31, 2013 Crofton Bluffs Expired Interest Rate Contracts [Member]		Dec. 31, 2012 Crofton Bluffs Expired Interest Rate Contracts [Member]		Dec. 31, 2013 Walnut Creek Interest rate contracts Swap 1		Dec. 31, 2012 Walnut Creek Interest rate contracts Swap 1		Dec. 31, 2013 Walnut Creek Interest rate contracts Swap 2		Dec. 31, 2012 Walnut Creek Interest rate contracts Swap 2		Dec. 31, 2013 WCEP Holdings, LLC Interest rate contracts Swap 1		Dec. 31, 2012 WCEP Holdings, LLC Interest rate contracts Swap 1		Dec. 31, 2013 WCEP Holdings, LLC Interest rate contracts Swap 2		Dec. 31, 2012 WCEP Holdings, LLC Interest rate contracts Swap 2
Derivative [Line Items]
Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments		$ 6
Fixed swap rate paid			3.18%		3.42%		3.03%		4.985%		4.29%		3.46%		2.21%		3.57%		2.96%	[1]			0.83%	[1]			2.75%	[1]			0.78%	[1]			0.81%	[2]			3.54%	[2]			0.79%	[2]			4.00%	[2]
Notional value			48	65	30	108	103	0	65	0	106	112	62	64	181	189	60	60	45	[1]	0	[1]	0	[1]	47	[1]	23	[1]	0	[1]	0	[1]	24	[1]	0	[2]	181	[2]	375	[2]	0	[2]	0	[2]	26	[2]	48	[2]	0	[2]
Payments for Fees	$ 6

[1] During the fourth quarter of 2013, the existing interest rate swaps for the Broken Bow and Crofton Bluffs projects expired and the forward starting swaps became effective.

[2] During the second quarter of 2013, the existing interest rate swaps for the Walnut Creek Project expired and, in conjunction with the conversion to term loans, the forward starting swaps became effective.