Income Taxes (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended	1 Months Ended	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2011	Apr. 30, 2010 Low-Income Housing Properties [Member]	Sep. 30, 2011 Low-Income Housing Properties [Member]	Sep. 30, 2010 Low-Income Housing Properties [Member]	Sep. 30, 2011 Low-Income Housing Properties [Member]	Sep. 30, 2010 Low-Income Housing Properties [Member]	Jan. 30, 2011 Investment in Refined Coal Facility [Member]	Sep. 30, 2011 Investment in Refined Coal Facility [Member]	Sep. 30, 2011 Investment in Refined Coal Facility [Member]
Schedule of Equity Method Investments [Line Items]
Cash payments to acquire equity method investment						$ 6					$ 48		$ 48
Income tax benefit, including tax credits, from equity method investment							9	7	27	18		4	11
Equity in net losses of unconsolidated entities	(7)	(8)	(20)	(16)			5	4	17	12
Interest expense	118	126	358	354			2	3	6	4
Tax credits from equity method investment							7	4	18	12
Income Taxes (Additional) (Textual) [Abstract]
Effective tax rate	32.30%	37.30%	34.00%	39.80%
Increase in the bonus depreciation allowance low			50.00%
Increase in the bonus depreciation allowance high			100.00%
Percentage of deduction that applies to qualifying property					100.00%
Expected decrease in cash taxes due to acceleration of depreciation deduction on current year capital expenditures					$ 190