Income Taxes - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended				12 Months Ended				1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2013 Subsequent Event [Member]	Dec. 31, 2012 2012 Audit [Member]	Dec. 31, 2012 2013 Audit [Member]	Dec. 31, 2012 Federal [Member]	Dec. 31, 2012 State [Member]	Jan. 31, 2011 Investment in Refined Coal Facility [Member]	Dec. 31, 2012 Investment in Refined Coal Facility [Member]	Dec. 31, 2011 Investment in Refined Coal Facility [Member]	Apr. 30, 2010 Low-Income Housing Properties [Member]	Dec. 31, 2012 Low-Income Housing Properties [Member]	Dec. 31, 2011 Low-Income Housing Properties [Member]	Dec. 31, 2010 Low-Income Housing Properties [Member]
Schedule of Equity Method Investments [Line Items]
Reduction in provision for income taxes due to tax audit settlements	$ 4	$ 10	$ 12	$ 8
Increase in diluted earnings per share due to tax audit settlements		$ 0.02	$ 0.03	$ 0.02
Expected time of completion of IRS audits						12 months	24 months
Increase in provision for income taxes due to deferred state tax rate changes			3	37
Increase in provision for income taxes due to current state tax rate changes				5
Beginning state tax rate, current				6.25%
Ending state tax rate, current				6.75%
Tax expense due to increase in provincial tax rates in Ontario		5
Reduction in provision for income taxes due to state net operating loss and credit carry-forwards		5	4	4
Reduction in provision for income taxes due to Federal net operating loss carry-forwards		8
Cash payments to acquire equity method investment										48			6
Equity in net losses of unconsolidated entities		(46)	(31)	(21)							(7)	(6)		(24)	(23)	(19)
Income tax benefit, including tax credits, from equity method investment											21	17		38	38	26
Interest expense		488	481	473										7	8	5
Tax credits from equity method investment														26	26	16
Unremitted earnings in foreign subsidiaries		850
Increase in valuation allowance due to acquisition		20
Net operating loss carry-forwards								91	1,600
Operating loss carry-forwards, expiration date								Expiration dates 2032	Expiration dates 2032
Capital loss carry-forward		104
Capital loss carry-forward, expiration date		Expiration date 2014
State tax credit carry-forward									42
Net unrecognized tax benefits that would impact effective tax rate in future period		38
Accrued interest in balance sheet	7	7	7
Accrued interest		2	2	3
Liabilities for unrecognized tax benefits including accrued interest that may be reversed within the next 12 months		14
Deferred tax assets related to unrecognized tax benefits that may be reversed within the next 12 months		$ 3
Percentage of Bonus Depreciation allowance					50.00%