Restructuring Activities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012 positions
Restructuring Cost and Reserve [Line Items]
Number of expected positions to be eliminated	200
Severance and other employee benefits due to employees affected by planned shutdowns	$ 9
Fisk Station
Restructuring Cost and Reserve [Line Items]
Tax basis of plant	58
Crawford Station
Restructuring Cost and Reserve [Line Items]
Tax basis of plant	$ 80