Other Non-Operating Expense - Narrative (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended		0 Months Ended	3 Months Ended
	Dec. 31, 2014 MW	Dec. 31, 2013	Dec. 31, 2012	Oct. 13, 2014	Sep. 30, 2014 MW	Dec. 31, 2014	Sep. 30, 2014 MW	Jul. 02, 2014	Mar. 31, 2012	Jun. 25, 2014
Schedule of Other Nonoperating Income (Expense) [Line Items]
Gain (Loss) on Disposition of Business	$ 358	$ 26	$ 219
Production Capacity (MW)	2,072					2,072
Other Nonoperating Expense	128	129	50
Entek
Schedule of Other Nonoperating Income (Expense) [Line Items]
Gain (Loss) on Disposition of Business						4
Investment In Affiliate Ownership Percentage Sold					49.62%		49.62%
Equity Method Investment, Purchase Price Agreement				125	125
Production Capacity (MW)					364		364
Equity Method Investment, Other than Temporary Impairment				68	86		18
Other Nonoperating Expense	86	0	0
Silver Ridge Power
Schedule of Other Nonoperating Income (Expense) [Line Items]
Equity Method Investment, Purchase Price Agreement								179
Equity Method Investment, Other than Temporary Impairment	42
Equity Method Investment, Ownership Percentage Sold								50.00%
Equity Method Investment, Net Sales Proceeds								179
Other Nonoperating Expense	42	0	0
Elsta
Schedule of Other Nonoperating Income (Expense) [Line Items]
Production Capacity (MW)		630
Other Nonoperating Expense	0	129	0
Equity Method Investments		240
Equity Method Investments, Fair Value Disclosure		111
China generation and wind
Schedule of Other Nonoperating Income (Expense) [Line Items]
Equity Method Investment, Other than Temporary Impairment									32
Other Nonoperating Expense	0	0	32
InnoVent
Schedule of Other Nonoperating Income (Expense) [Line Items]
Equity Method Investment, Other than Temporary Impairment									17
Other Nonoperating Expense	$ 0	$ 0	$ 17
Masinloc Subsidiary
Schedule of Other Nonoperating Income (Expense) [Line Items]
Investment In Affiliate Ownership Percentage Sold										45.00%