Changes in Fair Value of Assets Measured Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	$ 37	$ 38	$ 37	$ 38
Realized in earnings
Unrealized in other comprehensive income		(2)		(1)
Purchases
Sales
Settlements				(1)
Ending Balance	37	36	37	36
Private Placement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	24	25	24	25
Realized in earnings
Unrealized in other comprehensive income		(2)		(1)
Purchases
Sales
Settlements				(1)
Ending Balance	24	23	24	23
Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning Balance	13	13	13	13
Realized in earnings
Purchases
Sales
Ending Balance	$ 13	$ 13	$ 13	$ 13