Capital Structure - Components of Accumulated Other Comprehensive Loss (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Equity [Abstract]
Unrealized gains on available-for-sale securities, beginning balance	$ 11
Unrealized losses on available-for-sale securities, net of income taxes	(4)
Unrealized gains on available-for-sale securities, ending balance	7
Foreign currency translation adjustments, beginning balance	(1)
Foreign currency translation adjustments
Foreign currency translation adjustments, ending balance	(1)
Defined benefit plans, beginning balance	(196)
Defined benefit plans	5
Expense reclassified into operations from other comprehensive income, net of $9 and $36, respectively, income tax benefits	15
Balances at September 30, 2013	(176)
Change in fair value of derivative instruments, beginning balance	(271)
Change in fair value of derivative instruments	6
Change in fair value of derivative instruments, expense reclassified into operations from other comprehensive income	61
Change in fair value of derivative instruments, ending balance	(204)
Accumulated other comprehensive income, net of tax, beginning balance	(457)
Unrealized losses on available-for-sale securities, net of $3 income tax benefit	(4)
Defined benefit plans, net of $3 of income taxes	5
Change in fair value of derivative instruments, net of $3 of income taxes	6
Expense reclassified into operations from other comprehensive income, Total	76
Accumulated other comprehensive income, net of tax, Ending balance	$ (374)