Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	30.00%	27.00%	33.00%	27.00%
Valuation Allowances and Reserves, Charged to Cost and Expense			$ 132
Impairment of Long-Lived Assets Held-for-use	0	0	300	0
Impairment Of Long Lived Assets Held For Use After Tax			342
Production tax credits	36	35	161	147
Deferred income tax benefit associated with convertible investment tax credits	$ 29	$ 14	$ 62	$ 37