Income Taxes (Narrative) (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Non-Variable Interest Entities [Line Items]
Federal statutory rate	35.00%	35.00%	35.00%
Net deferred tax asset	$ 1,400,000,000
Capital losses carryforward period in years	5 years
Taxable income projections, years	15 years
Maximum taxable income projections, years	20 years
Total deferred tax assets	1,400,000,000
Capital loss carryforward			153,000,000
NOL carryforward			1,300,000,000
Minimum tax credit carryforward			22,000,000
Non Variable Interest Entities [Member]
Non-Variable Interest Entities [Line Items]
Net deferred tax asset	1,446,000,000		1,745,000,000
Valuation allowance	167,000,000		236,000,000
Valuation allowance decrease	$ 69,000,000