Derivatives (Details) In Millions, unless otherwise specified	Dec. 31, 2011 USD ($)	Dec. 31, 2011 Derivatives not designated as hedges [Member] USD ($)	Dec. 31, 2011 Derivatives not designated as hedges [Member] EUR (€)	Dec. 31, 2011 Fair Value Hedging [Member] USD ($)	Dec. 31, 2011 Fair Value Hedging [Member] EUR (€)	Dec. 31, 2011 Power [Member] MWh	Dec. 31, 2011 Gas [Member] MMBTU	Dec. 31, 2011 Hedge Maturity Date January 2022 [Member] USD ($)	Dec. 31, 2011 Hedge Maturity Date January 2022 [Member] Cash Flow Hedging [Member] USD ($)	Dec. 31, 2011 Hedge Maturity Date December 2022 [Member] USD ($)	Dec. 31, 2011 Hedge Maturity Date December 2022 [Member] Cash Flow Hedging [Member] USD ($)	Dec. 31, 2011 Hedge Maturity Date April 2022 [Member] USD ($)	Dec. 31, 2011 Hedge Maturity Date April 2022 [Member] Cash Flow Hedging [Member] USD ($)
Energy-related derivative contracts
Net Purchased MWHs						1,000,000
Net Purchased mmBtu							189,000,000
Longest Hedge Date						2012	2017
Longest Non-Hedge Date						2012	2017
Notional amount of interest rate derivatives
Notional Amount								$ 100		$ 300		$ 300
Notional Amount, Fair Value	350
Notional Amount of interest rate derivatives, Total	1,050
Interest Rate Received				0.0415	0.0415				3-month LIBOR		3-month LIBOR		3- month LIBOR
Interest Rate Paid				3-month LIBOR + 1.96% spread	3-month LIBOR + 1.96% spread				0.0222		0.0290		0.0266
Hedge Maturity Date				May 01, 2014	May 01, 2014				Jan. 01, 2022		Dec. 01, 2022		Apr. 01, 2022
Fair Value Gain (Loss) Dec 31, 2011	(20)			13					(1)		(17)		(15)
Notional Amount			18.1		9.2
Forward Rate		1.317		1.371
Hedge Maturity Date				Various through March 2014	Various through March 2014
Fair Value Gain (Loss) Dec. 31, 2011	$ (1)	$ 0		$ (1)