Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	67.00%	25.00%
Valuation Allowances and Reserves, Charged to Cost and Expense	$ 132
Impairment of Long-Lived Assets Held-for-use	300	0
Impairment Of Long Lived Assets Held For Use After Tax	342
Production tax credits	59	61
Deferred income tax benefit associated with convertible investment tax credits	$ 13	$ 12