Changes in Fair Value of Assets Measured Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance at January 1	$ 41	$ 66	$ 93
Realized in earnings	0	2	6
Unrealized in other comprehensive income	0	1	(2)
Purchases	0	17	3
Sales	(3)	(45)	(16)
Settlements	0	0	(18)
Balance at December 31	38	41	66
Private Placements/Venture Capital
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance at January 1	25	14	24
Realized in earnings	0	1	6
Unrealized in other comprehensive income	0	0	(4)
Purchases	0	17	3
Sales	0	(7)	(13)
Settlements	0	0	(2)
Balance at December 31	25	25	14
Auction Rate Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance at January 1	16	52	69
Realized in earnings	0	1	0
Unrealized in other comprehensive income	0	1	2
Purchases	0	0	0
Sales	(3)	(38)	(3)
Settlements	0	0	(16)
Balance at December 31	$ 13	$ 16	$ 52