Fair Value Measurements (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2012 USD ($)	Sep. 30, 2013 USD ($) Swap	Sep. 30, 2012 USD ($) Swap	Sep. 30, 2011 USD ($)	Sep. 30, 2013 Series Five USD ($) Swap	Mar. 31, 2011 Series One USD ($)	Mar. 31, 2011 Series Two USD ($) Swap	Mar. 31, 2011 Series Three USD ($) Swap	Sep. 30, 2013 Series Four USD ($)	Sep. 30, 2013 Cross-currency interest rate swaps JPY (¥)	Sep. 30, 2012 Cross-currency interest rate swaps JPY (¥)	Sep. 30, 2013 Unrealized Gains [Member] USD ($)	Sep. 30, 2012 Unrealized Gains [Member] USD ($)	Sep. 30, 2013 Unrealized Losses [Member] USD ($)	Sep. 30, 2012 Unrealized Losses [Member] USD ($)
Derivative [Line Items]
Number of fixed to floating interest rate swaps outstanding		10	8
Fixed to floating interest rate swaps entered					$ 800,000,000	$ 100,000,000	$ 300,000,000	$ 450,000,000	$ 125,000,000
Coupon rate of notes					5.50%	5.80%	4.875%	1.75%	7.70%
Number of fixed to floating interest rate swaps entered					4		2	5
Number of cross-currency interest rate swaps outstanding		5	3
Cross-currency interest rate swaps outstanding										25,000,000,000	20,000,000,000
Unrealized gains (losses) on investments in marketable common stock												7,000,000	5,000,000	0	0
Impairment charge	14,000,000	586,000,000	53,000,000	0
Investment after impairment	0
Fair value of long term debt		$ 5,700,000,000	$ 6,300,000,000