Income Taxes - Tax Carryforwards Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Foreign tax credits [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 119
Tax credit carryforward, expiration date(s)	2015-2021
Charitable contributions [Member]
Operating Loss Carryforwards [Line Items]
Other tax carryforward	27
Other tax carryforward, expiration date	2016
Texas margins tax credit [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	37
Tax credit carryforward, expiration date(s)	2026
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	1,728
Net operating loss carryforward, expiration date(s)	2031
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	825
Net operating loss carryforward, expiration date(s)	2016 - indefinite
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	$ 4,609
Net operating loss carryforward, expiration date(s)	2012-2030