Income Taxes (Narrative) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Non-Variable Interest Entities [Line Items]
Net deferred tax asset	$ 1,100,000,000
Capital losses carryforward period in years	5 years
Maximum taxable income projections, years	20 years
Total deferred tax assets	1,100,000,000
Non Variable Interest Entities [Member]
Non-Variable Interest Entities [Line Items]
Net deferred tax asset	1,146,000,000	1,199,000,000
Valuation allowance	127,000,000	146,000,000
Valuation allowance decrease	$ 19,000,000