Income Taxes - Tax Carryforwards Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Foreign Tax Credits [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	433
Foreign Tax Credits [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, expiration date(s)	Dec. 31, 2017
Foreign Tax Credits [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward, expiration date(s)	Dec. 31, 2021
Texas Margins Tax Credit [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	36
Tax credit carryforward, expiration date(s)	Dec. 31, 2026
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	809
Net operating loss carryforwards, expiration date(s)	2031
Federal [Member] | Alternative Minimum Tax Credit [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	17
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	884
Net operating loss carryforwards, expiration date(s)	2016 - Indefinite
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	4,560
State [Member] | Minimum [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration date(s)	2012
State [Member] | Maximum [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards, expiration date(s)	2031