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Debt - Schedule of Long-term Debt Instruments (Details) - USD ($)	Jun. 30, 2019	Mar. 04, 2019	Oct. 04, 2018	Sep. 30, 2018
Debt Instrument [Line Items]
Total long-term debt	$ 3,685,000,000			$ 3,085,000,000
Original issue (premium) / discount on unsecured senior notes and debentures	225,000			(4,439,000)
Debt issuance cost	30,640,000			20,774,000
Current maturities	125,000,000			575,000,000
Long-term debt	3,529,135,000			2,493,665,000
Unsecured 8.50% Senior Notes, due March 2019
Debt Instrument [Line Items]
Total long-term debt	0			$ 450,000,000
Interest rate				8.50%
Unsecured 3.00% Senior Notes, due 2027
Debt Instrument [Line Items]
Total long-term debt	$ 500,000,000			$ 500,000,000
Interest rate	3.00%			3.00%
Unsecured 5.95% Senior Notes, due 2034
Debt Instrument [Line Items]
Total long-term debt	$ 200,000,000			$ 200,000,000
Interest rate	5.95%			5.95%
Unsecured 5.50% Senior Notes, due 2041
Debt Instrument [Line Items]
Total long-term debt	$ 400,000,000			$ 400,000,000
Interest rate	5.50%			5.50%
Unsecured 4.15% Senior Notes, due 2043
Debt Instrument [Line Items]
Total long-term debt	$ 500,000,000			$ 500,000,000
Interest rate	4.15%			4.15%
Unsecured 4.125% Senior Notes, due 2044
Debt Instrument [Line Items]
Total long-term debt	$ 750,000,000			$ 750,000,000
Interest rate	4.125%			4.125%
Medium-term note Series A, 1995-1, 6.67%, due 2025
Debt Instrument [Line Items]
Total long-term debt	$ 10,000,000			$ 10,000,000
Interest rate	6.67%			6.67%
Unsecured 6.75% Debentures, due 2028
Debt Instrument [Line Items]
Total long-term debt	$ 150,000,000			$ 150,000,000
Interest rate	6.75%			6.75%
Floating-rate term loan, due September 2019
Debt Instrument [Line Items]
Total long-term debt	$ 125,000,000			$ 125,000,000
Maximum borrowing capacity	200,000,000			200,000,000
Unsecured 4.30% Senior Notes, due 2048
Debt Instrument [Line Items]
Total long-term debt	$ 600,000,000		$ 600,000,000	0
Interest rate	4.30%		4.30%
Unsecured 4.125% Senior Notes, due 2049
Debt Instrument [Line Items]
Total long-term debt	$ 450,000,000	$ 450,000,000		$ 0
Interest rate	4.125%	4.125%