Debt (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended				12 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended		1 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Sep. 09, 2011	Dec. 31, 2011 Due In 2013 [Member]	Dec. 31, 2011 7.75% Debentures Due 2026 [Member]	Sep. 09, 2011 2.13% Notes Due 2016 [Member]	Dec. 31, 2011 2.13% Notes Due 2016 [Member]	Sep. 09, 2011 3.35% Notes Due 2021 [Member]	Dec. 31, 2011 3.35% Notes Due 2021 [Member]	Sep. 09, 2011 4.85% Notes Due 2041 [Member]	Dec. 31, 2011 4.85% Notes Due 2041 [Member]	May 31, 2010 5.72% Notes Due 2040 [Member]	Dec. 31, 2011 5.72% Notes Due 2040 [Member]	Aug. 31, 2011 New Credit Facility [Member]	Aug. 31, 2011
Debt Instrument [Line Items]
Amount of issued debt					$ 2,000,000,000			$ 500,000,000		$ 900,000,000		$ 600,000,000		$ 728,000,000
Senior note, interest rate									2.13%		3.35%		4.85%		5.72%
Senior note, maturity date						2013		2016		2021		2041		2040
Redemption of debt						500,000,000	84,000,000
Principal amount of debt exchanged														611,000,000
Premium paid														158,000,000
Notes issued														117,000,000
Premiums paid in connection with early extinguishments of debt	46,000,000	48,000,000
Cash premium for debt exchange														41,000,000
Revolving credit facility																1,500,000,000	1,500,000,000
Revolving credit facility expiration date																August 2016	June 2012
Additional amount to increase credit facility, at banks' discretion		500,000,000
Long-term debt, due in year two	153,000,000	153,000,000
Long-term debt, due in year five	954,000,000	954,000,000
Interest payment		$ 326,000,000	$ 337,000,000	$ 286,000,000