Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Tax Disclosure [Abstract]
Effective income tax rate (as a percent)	26.00%	29.00%	35.00%	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	66	50	125	112
Deferred income tax benefit associated with convertible investment tax credits	$ 21	$ 10	$ 33	$ 23