Fair Value Measurements (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Fair Value of Financial Instruments
Subsidiary preferred stock, effective interest rate (as a percent)	4.00%		4.00%
Carrying Value	$ 3,983,490		$ 4,448,888
Fair Value	4,251,473		5,142,918
Subsidiary preferred stock, carrying value	69,188		69,188
Subsidiary preferred stock, fair value	69,000		68,625
Securities available-for-sale	117,218		200,577
Trading equity securities, fair value	3,200		52,705
Securities classified as available-for-sale and trading	117,200
2.35% senior notes due September 2016
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	2.56%		6.42%
Carrying Value	349,820
Fair Value	354,694
Interest rate on senior notes due (as a percent)	2.35%	2.35%
6.15% senior notes due February 2018
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	6.42%		6.42%
Carrying Value	969,928		968,708
Fair Value	1,097,480		1,164,813
Interest rate on senior notes due (as a percent)	6.15%
9.25% senior notes due January 2019
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	9.33%		9.33%
Carrying Value	339,607		1,125,000
Fair Value	428,733		1,492,819
Interest rate on senior notes due (as a percent)	9.25%
5.00% senior notes due September 2020
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	5.20%		5.20%
Carrying Value	697,947		697,648
Fair Value	731,955		770,707
Interest rate on senior notes due (as a percent)	5.00%
4.625% senior notes due September 2021
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	4.75%		4.75%
Carrying Value	698,148		697,907
Fair Value	709,793		755,517
Interest rate on senior notes due (as a percent)	4.625%
5.10% senior notes due September 2023
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	5.26%
Carrying Value	348,765
Fair Value	349,731
Interest rate on senior notes due (as a percent)	5.10%	5.10%
Revolving Credit Facility
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	2.28%		2.17%
Carrying Value	170,000		890,000
Fair Value	170,000		890,000
Commercial paper
Fair Value of Financial Instruments
Effective Interest Rate (as a percent)	0.45%
Carrying Value	329,844
Fair Value	329,844
Other
Fair Value of Financial Instruments
Carrying Value	10,243		437
Fair Value	$ 10,243		$ 437