Debt - Narrative (Details)	3 Months Ended		6 Months Ended
	Jan. 31, 2018 USD ($)	Jan. 31, 2017 USD ($)	Apr. 30, 2018 USD ($)	Apr. 30, 2017 USD ($)	Jul. 31, 2018 USD ($)	Oct. 31, 2017 USD ($)	Jul. 31, 2016 USD ($)	Jan. 31, 2012 USD ($)
Debt Instrument [Line Items]
Notes Issued	$ 1,100,000,000
Senior Notes	$ 1,051,000,000
Percentage of Aggregate Principal	0.7250
Notes Payable	$ 1,003.80
Line of Credit Facility, Increase (Decrease) for Period, Description	1700
Debt Instrument, Coupon Rate, Increase (Decrease)	0.0675	0.0650
Long-term Line of Credit	$ 1,600,000,000
Amortization	4,000,000
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000
Payments of Debt Issuance Costs			$ 33,000,000	$ 18,000,000
Debt Instrument, Interest Rate, Stated Percentage			6.75%
Financial Services Operations | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 275,000,000			$ 700,000,000	$ 269,000,000	$ 400,000,000	$ 500,000,000
Financial Services Operations | VFN Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	425,000,000
Financial Services Operations | Trac Funding Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100,000,000
Financial Services Operations | Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		82,000,000
Periodic Payment, Principal		$ 2,000,000						$ 9,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Gain (Loss) on Extinguishment of Debt	30,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Gain (Loss) on Extinguishment of Debt	$ 16,000,000
Line of Credit [Member] | Manufacturing Operations [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Net			$ 0			9,000,000
Line of Credit [Member] | Financial Services Operations
Debt Instrument [Line Items]
Debt Issuance Costs, Net			$ 1,000,000			$ 2,000,000