Long-Term Debt (Parenthetical) (Details) (USD $)	Sep. 30, 2012 5.8 % Due in 2013	Sep. 30, 2013 4.875 % Due in 2013	Sep. 30, 2012 4.875 % Due in 2013	Sep. 30, 2013 Floating Rate Notes Due in 2014	Sep. 30, 2012 Floating Rate Notes Due in 2014	Sep. 30, 2013 1.75 % Due in 2014	Sep. 30, 2012 1.75 % Due in 2014	Sep. 30, 2013 7.7 % Due in 2015	Sep. 30, 2012 7.7 % Due in 2015	Sep. 30, 2013 5.5 % Due in 2016	Sep. 30, 2012 5.5 % Due in 2016	Sep. 30, 2013 7.125 % Due in 2017	Sep. 30, 2012 7.125 % Due in 2017	Sep. 30, 2013 2.6 % Due in 2017	Sep. 30, 2012 2.6 % Due in 2017	Dec. 31, 2011 2.6 % Due in 2017	Sep. 30, 2013 2.355 % Due in 2017	Sep. 30, 2012 2.355 % Due in 2017	Mar. 31, 2012 2.355 % Due in 2017	Sep. 30, 2013 5.0 % Due in 2020	Sep. 30, 2012 5.0 % Due in 2020	Sep. 30, 2013 4.25% Due in 2021	Sep. 30, 2012 4.25% Due in 2021	Sep. 30, 2013 3.75 % Due in 2022	Sep. 30, 2012 3.75 % Due in 2022	Dec. 31, 2011 3.75 % Due in 2022	Sep. 30, 2013 6.0 % Due in 2036	Sep. 30, 2012 6.0 % Due in 2036	Sep. 30, 2013 5.7 % Due in 2041	Sep. 30, 2012 5.7 % Due in 2041	Sep. 30, 2013 5.25 % Due in 2042	Sep. 30, 2012 5.25 % Due in 2042	Dec. 31, 2011 5.25 % Due in 2042	Sep. 30, 2013 6.95 % Due in 2046	Sep. 30, 2012 6.95 % Due in 2046
Debt Instrument [Line Items]
Interest rate on notes	5.80%	4.875%	4.875%			1.75%	1.75%	7.70%	7.70%	5.50%	5.50%	7.125%	7.125%	2.60%	2.60%	2.60%	2.355%	2.355%	2.355%	5.00%	5.00%	4.25%	4.25%	3.75%	3.75%	3.75%	6.00%	6.00%	5.70%	5.70%	5.25%	5.25%	5.25%	6.95%	6.95%
Aggregate principal amount of debt	$ 100,000,000		$ 300,000,000	$ 350,000,000	$ 350,000,000	$ 450,000,000	$ 450,000,000	$ 125,000,000	$ 125,000,000	$ 800,000,000	$ 800,000,000	$ 150,000,000	$ 150,000,000	$ 400,000,000	$ 400,000,000	$ 400,000,000	$ 46,000,000	$ 46,000,000	$ 46,000,000	$ 500,000,000	$ 500,000,000	$ 500,000,000	$ 500,000,000	$ 450,000,000	$ 450,000,000	$ 450,000,000	$ 400,000,000	$ 400,000,000	$ 300,000,000	$ 300,000,000	$ 250,000,000	$ 250,000,000	$ 250,000,000	$ 125,000,000	$ 125,000,000