Notes Payable and Long-Term Debt - Footnote Narrative (Details) - USD ($)		1 Months Ended	12 Months Ended
	Jun. 30, 2016	Sep. 30, 2015	Aug. 31, 2017	Aug. 31, 2016
Debt Instrument [Line Items]
Receivables Securitization Facility, Amount			$ 700,000,000
Availability under Securitization Facility			618,000,000
Long-term Debt, Fair Value			2,100,000,000
Notes payable			1,988,215,000	$ 2,731,479,000
Increase (Decrease) in Fair Value of Hedged Item in Interest Rate Fair Value Hedge			12,800,000	9,800,000
Debt Instrument, Term	10 years
Long-term Debt			$ 2,142,400,000
Unsecured debt | Minimum
Debt Instrument [Line Items]
Interest rate			1.30%
Unsecured debt | Maximum
Debt Instrument [Line Items]
Interest rate			15.25%
Five-year revolving facilities | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding			$ 480,000,000	700,000,000
Debt Instrument, Term			5 years
Five-year revolving facilities | Line of credit | Revolving credit facility | Minimum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			0.00%
Five-year revolving facilities | Line of credit | Revolving credit facility | Maximum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			1.45%
Three-Year Revolving Facility [Member] | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Debt Instrument, Term			3 years
Uncommitted lines of credit | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Long-term Line of Credit, Noncurrent			$ 433,900,000
Other international subsidiaries, lines of credit | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding			168,400,000
Line Of Credit, Collateralized Amount			15,400,000
Bilateral, uncommitted revolving facilities available to multiple subsidiaries [Member] | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Short-term Debt, Fair Value			100,000,000
Miscellaneous short-term notes payable | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Line of credit facility, amount outstanding			$ 13,100,000
Term loans from cooperative and other banks | Line of credit | Revolving credit facility
Debt Instrument [Line Items]
Interest rate			5.59%
Long-term Debt			$ 15,000,000	45,000,000
Private placement, payable in equal installments beginning in 2014 through 2018 | Unsecured debt
Debt Instrument [Line Items]
Interest rate			6.18%
Debt Instrument, Face Amount			$ 400,000,000
Long-term Debt			$ 80,000,000	160,000,000
Private placement, payable in installments through 2018 | Unsecured debt
Debt Instrument [Line Items]
Interest rate			5.60%
Debt Instrument, Face Amount			$ 60,000,000
Long-term Debt			4,615,000	13,846,000
Private placement, payable in equal installments beginning in 2014 through 2018 | Unsecured debt
Debt Instrument [Line Items]
Long-term Debt			$ 10,000,000	20,000,000
Private placement, payable in equal installments beginning in 2014 through 2018 | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest rate			5.78%
Debt Instrument, Face Amount			$ 50,000,000
Private placement, payable in equal installments beginning in 2017 through 2021 | Unsecured debt
Debt Instrument [Line Items]
Long-term Debt			$ 80,000,000	100,000,000
Private placement, payable in equal installments beginning in 2017 through 2021 | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest rate			4.00%
Debt Instrument, Face Amount			$ 100,000,000
Other notes and contracts | Secured debt
Debt Instrument [Line Items]
Long-term Debt			62,652,000	76,147,000
Notes Payable, Other Payables [Member] | Notes Payable, Other Payables [Member] | Revolving credit facility
Debt Instrument [Line Items]
Notes payable			1,695,423,000	$ 1,803,174,000
Master participation agreements | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Short-term bank loans and notes payable current borrowing capacity			94,100,000
Notes payable			$ 29,400,000
Master participation agreements | Notes Payable, Other Payables [Member] | Minimum
Debt Instrument [Line Items]
Interest rate			2.61%
Master participation agreements | Notes Payable, Other Payables [Member] | Maximum
Debt Instrument [Line Items]
Interest rate			4.45%
Recourse loan commitments | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Short-term bank loans and notes payable current borrowing capacity			$ 220,200,000
Short-term debt, maximum borrowing capacity			265,000,000
Notes payable			$ 144,100,000
Interest rate			2.45%
Short-Term Notes Payable, Surplus Funds Program [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Notes payable			$ 119,300,000
Short-Term Notes Payable, Surplus Funds Program [Member] | Notes Payable, Other Payables [Member] | Minimum
Debt Instrument [Line Items]
Interest rate			0.10%
Short-Term Notes Payable, Surplus Funds Program [Member] | Notes Payable, Other Payables [Member] | Maximum
Debt Instrument [Line Items]
Interest rate			0.90%
Committed Term Loans, September 2015 [Member] | Secured debt
Debt Instrument [Line Items]
Debt Instrument, Term	10 years	10 years
Debt Instrument, Face Amount	$ 600,000,000		$ 600,000,000.0
Long-term Debt			300,000,000
Amount re-advanced			$ 130,000,000
Committed Term Loans, September 2015 [Member] | Secured debt | London Interbank Offered Rate (LIBOR) [Member] | Minimum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			1.50%
Committed Term Loans, September 2015 [Member] | Secured debt | London Interbank Offered Rate (LIBOR) [Member] | Maximum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			2.00%
Committed Term Loans, September 2015 [Member] | Secured debt | Base Rate [Member] | Minimum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			0.50%
Committed Term Loans, September 2015 [Member] | Secured debt | Base Rate [Member] | Maximum
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			1.00%