Borrowings (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended											9 Months Ended		9 Months Ended
	Sep. 30, 2012	May 31, 2012	Dec. 31, 2011	Sep. 30, 2012 2012 Revolving Credit Facility [Member]	Dec. 31, 2012 2012 Revolving Credit Facility [Member] Subsequent Event [Member]	Oct. 31, 2012 2012 Revolving Credit Facility [Member] Subsequent Event [Member]	Oct. 31, 2012 Revolving Credit Facility Maturing November Two Thousand Twelve [Member] Subsequent Event [Member]	Dec. 31, 2012 Revolving Credit Facility Maturing December Two Thousand Twelve [Member] Subsequent Event [Member]	May 17, 2012 Commercial Paper [Member]	May 13, 2011 Commercial Paper [Member]	Oct. 14, 2009 Commercial Paper [Member]	Mar. 31, 2011 Line of Credit [Member] 2012 Revolving Credit Facility [Member]	Sep. 30, 2012 Maximum Amount [Member] 2012 Revolving Credit Facility [Member]	Apr. 30, 2012 Maximum Amount [Member] 2012 Revolving Credit Facility [Member]	Sep. 30, 2012 Unsecured Debt 2015 Note [Member]	May 31, 2012 Unsecured Debt 2015 Note [Member]	Sep. 30, 2012 Unsecured Debt 2022 Note [Member]	May 31, 2012 Unsecured Debt 2022 Note [Member]
Debt [Line Items]
Line of credit facility, borrowing capacity									$ 3,785	$ 3,500	$ 3,000	$ 3,500		$ 3,785
Additional amount available, subject to lender credit approval				4,785									1,000
Line of credit facility covenant terms ratio				3.00%
Line of credit facility,covenant terms	("LIBOR") plus a spread. The 2012 credit facility requires the Company not to exceed a maximum leverage ratio (ratio of net debt to earnings before interest, taxes, depreciation and amortization, where net debt equals total debt less unrestricted cash)
Line of credit facility, covenant compliance	Satisfied with a ratio of approximately 1 to 1 at September 30, 2012.
Revolving credit facility				100		100
Roll over of borrowings					100	100
Interest rate				1.105%			1.085%	1.085%								1.375%		3.375%
Aggregate principal amount issued		1,500														750		750
Approximate annual interest expense															10		25
Unamortized discount	14														5
Debt issuance costs incurred																	7
Long-term borrowings	6,186		4,690
Long-term debt, fair value			$ 5,057