Other Non-Operating Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 MWh	Mar. 31, 2012
Component of Other Expense, Nonoperating [Line Items]
Other non-operating expense	$ 0	$ 49
Generation Capacity (MW)	125
Innovent [Member]
Component of Other Expense, Nonoperating [Line Items]
Other non-operating expense		17
Generation Capacity (MW)		75
Fair Value		19
Carrying Amount		36
Other Nonoperating Other [Member]
Component of Other Expense, Nonoperating [Line Items]
Other non-operating expense		1
China Generation [Member]
Component of Other Expense, Nonoperating [Line Items]
Other non-operating expense		31
Fair Value		133
Carrying Amount		$ 164