Income Taxes - Narrative (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Tax Disclosure
Tax effect of share-based compensation	$ 1,033,000,000	$ 433,000,000	$ 107,000,000
Valuation allowance, deferred tax assets	37,000,000	9,000,000
Tax-effected benefit to be recognized in additional paid in capital if net operating loss carryforward is utilized	2,170,000,000
Event Causing Ownership Change and Loss in Net Operating Loss and Tax Credit Carryforward, Cumulative Stock Ownership Change Threshhold	50.00%
Event Causing Ownership Change and Loss in Net Operating Loss and Tax Credit Carryforward, Change in Ownership Percentage Over Period	3 years
Unrecognized tax benefits, interest on income taxes expense	3,000,000
Unrecognized tax benefits, income tax penalties expense	1,000,000
Unrecognized tax benefits, income tax penalties and interest accrued	10,000,000	6,000,000
Unrecognized tax benefits	164,000,000	63,000,000	18,000,000	9,000,000
Unrecognized tax benefits that would impact effective tax rate	70,000,000
Income tax refundable	451,000,000	0
Increase in income tax refundable	451,000,000	0	0
Deferred income taxes	186,000,000	30,000,000	(23,000,000)
Internal Revenue Service (IRS)
Income Tax Disclosure
Operating loss carryforwards	5,830,000,000
State and Local Jurisdiction
Income Tax Disclosure
Operating loss carryforwards	7,620,000,000
Tax credit carryforward	$ 181,000,000