Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use	$ 1,295	$ 9		$ 1,971	$ 30
Write-Off Of Deferred Costs Related To Cancelled Mining Projects			$ 9		$ 30
Martin Lake Steam Electric Station, Sandow Steam Electric Station Unit 4 and Sandow Electric Station Unit 5 [Member] [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use				1,295
Big Brown Steam Electric Station [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use				$ 676