Changes in Fair Value of Assets Measured Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 37	$ 38
Realized in earnings	0	0
Unrealized in other comprehensive income	0	1
Purchases	0	0
Sales	0	0
Settlements	0	(1)
Ending Balance	37	38
Private Placement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	24	25
Realized in earnings	0	0
Unrealized in other comprehensive income	0	1
Purchases	0	0
Sales	0	0
Settlements	0	(1)
Ending Balance	24	25
Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	13	13
Realized in earnings	0	0
Unrealized in other comprehensive income	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Ending Balance	$ 13	$ 13