Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	26.00%	78.00%
Valuation Allowances and Reserves, Charged to Cost and Expense		$ 132
Impairment of Long-Lived Assets Held-for-use	0	300
Impairment Of Long Lived Assets Held For Use After Tax		342
Production tax credits	49	59
Deferred income tax benefit associated with convertible investment tax credits	$ 12	$ 13